The Arabic-Latin translation movements in the Middle Ages, whichparalleled that from Greek into Latin, led to the transformation ofalmost all philosophical disciplines in the medieval Latin world. Theimpact of Arabic philosophers such as al-Fārābī,Avicenna and Averroes on Western philosophy was particularly strong innatural philosophy, psychology and metaphysics, but also extended tologic and ethics.

Among the influential Arabic theories are: the logical distinctionbetween first and second intentions; the intension and remission ofelementary forms; the soul’s faculty of estimation and itsobject, the intentions; the conjunction between human intellect andseparate active intellect; the unicity of the material intellect(Averroism); naturalistic theories of miracles and prophecy; theeternity of the world and the concept of eternal creation; the activeintellect as giver of forms; the first cause as necessary being initself; the emanation of intelligences from the first cause; thedistinction between essence and existence; the theory of primaryconcepts; the concept of human happiness as resulting from perfectconjunction of the human intellect with the active intellect.

• 1. Transmission
• 2. Division of the Sciences
• 3. Logic
• 4. Natural Philosophy
  • 4.1 Eternity of the World
  • 4.2 The Elements in a Compound
  • 4.3 Spontaneous Generation
• 5. Psychology
  • 5.1 Estimation
  • 5.2 Active Intellect
  • 5.3 The Four Intellects
  • 5.4 Averroes’ Unicity Thesis
  • 5.5 Naturalistic Theories of Prophecy
• 6. Metaphysics
  • 6.1 The Subject of Metaphysics
  • 6.2 Primary Concepts
  • 6.3 Essence and Existence, Universals and Individuals
  • 6.4 The First Cause and the Emanation of the Intelligences
• 7. Ethics
• Bibliography
• Academic Tools
• Other Internet Resources
• Related Entries

1. Transmission

Arabic Philosophy was known in the Latin West through translations,and, to a small degree, through personal contacts between Christiansand Muslims, as in the case of Frederick II Hohenstaufen, who wasdirectly acquainted with a number of Muslim scholars. A small numberof Christian scholars, such as Ramón Martí andRamón Llull, knew Arabic themselves and drew on Arabic sourceswhen composing Latin works. Translations, however, were far moreinfluential. The first Arabic-Latin translations to transportphilosophical material into Latin Europe were the translations oftexts on medicine and natural philosophy produced towards the end ofthe eleventh century in Italy, most of them by the translatorConstantine the African, who, in contrast to later translators, triedto disguise the Arabic origin of his texts (Burnett 2006,22–24). In Spain, in the first half of the twelfth century,several important astrological texts were translated, such asAlbumasar’sGreat Introduction to Astrology, whichincorporated much material of the Aristotelian tradition (Lemay1962).

The translations of philosophical texts proper, such as byal-Kindī, by the anonymous author of theLiber decausis, by al-Fārābī, Isaac Israeli,al-Ghazālī and Avicenna, but also of Greek works transmittedin Arabic, assumed full pace in Toledo in the second half of thetwelfth century, where two very prolific translators worked: Gerard ofCremona and Dominicus Gundisalvi. It is likely thatal-Fārābī’s treatiseEnumeration of theSciences, translated twice, by Gerard and Gundisalvi, served as amodel for a coherent translation program. An indication of this isthat later Toledan translators such as Alfred of Shareshill, MichaelScot and Hermannus Alemannus filled in gaps inal-Fārābī’s list of disciplines which the earliertranslators had not covered (Burnett 2001). The translation movementwas also influenced by the philosophical preferences of Jewishscholars. Gundisalvi worked together with the Jewish scholar Avendauthwhen translating Avicenna’sDe anima, which Avendauthhad recommended for translation, and Gundisalvi’s othertranslations may also go back to such recommendations. The impressiveSpanish translation movement was motivated and fostered by severalfactors: the personal interest of individual translators; the demandfor scientific texts by the French schools; the availability of Arabicmanuscripts in cities newly conquered by the Christians; the patronageof the archbishop of Toledo; and by clerical interests in promotingLatin scientific culture in an Arabic-speaking Christian environment(Hasse 2006, 79–84).

The next important phase of the transmission were the translationsmade in Sicily and southern Italy by several translators associatedwith the Hohenstaufen or the papal court, the most productive of whichwere the Averroes translators Michael Scot and William of Luna. It wasonly about thirty years after Averroes’ death in 1198 that LatinAverroes translations became available in the newly developinguniversities (Gauthier 1982b). In 1255, the statutes of the Parisianarts faculty declared all known works of Aristotle mandatory readingfor the students – a very influential move, which muchcontributed to the rise of Averroes’ commentaries as theprincipal secondary literature of Latin university culture.

After about 1300, Arabic-Latin translation activities ceased almostentirely, to resume again after 1480. The Renaissance translationswere mostly produced by Italian Jews from Hebrew versions of Arabictexts, an exception being Andrea Alpago’s Avicenna translationsfrom Arabic, which were produced in Damascus (Tamani 1992; Burnett1999; Hasse 2016, ch. 3). The social context of these translations wasthe vibrant philosophical culture of Italian universities andespecially of Padua, and the patronage of Italian scholars belongingto the Italian nobility, who had been educated in these universities. The impact of these Renaissance translations, which isweaker than that of the medieval translations, remains largelyunexplored. It has aleady been shown that the new translationsinfluenced the logical and zoological discussions of the sixteenthcentury (Perfetti 2000, 106–109; Perfetti 2004,XVII–XVIII; Burnett 2013). In the second half of the sixteenthcentury, interest in Arabic philosophy and sciences declined, and withit the Arabic-(Hebrew-)Latin translation movement. At the same time,the new academic study of Arabic culture developed, which wasmotivated primarily by historical and philological, but not byphilosophical interests. From the seventeenth century onwards,translations into vernacular languages gradually replaced Latintranslations from Arabic (Bobzin 1992).

The corpus of Arabic philosophical texts translated into Latin wassubstantial: A recent publication lists 131 textual items (Burnett2005; see Kischlat 2000, 53–54, 196–198 for manuscriptdistribution; on Avicenna translations see Bertolacci 2011 and 2013b;on translator attribution see Hasse & Büttner 2018). Theintroduction of Arabic philosophy into Latin Europe led to thetransformation of almost all philosophical disciplines. The influenceis particularly dominant in natural philosophy, psychology andmetaphysics, but is also felt in logic and ethics. The Arabic impactis particularly strong in the thirteenth century, but some Arabictraditions, such as Averroes’ intellect theory, reach the highpoint of their influence in Latin Europe as late as around 1500 (Theinfluence of Jewish philosophers writing in Arabic, such as IbnGabirol and Maimonides, is not covered in this article).

2. Division of the Sciences

Arabic divisions of the sciences influenced the Latin West mainlythrough Dominicus Gundisalvi’ treatiseDivision ofPhilosophy (De divisione philosophiae). In this text,Gundisalvi reuses much material from his own abbreviating translationof al-Fārābī’sEnumeration of theSciences (Iḥṣāʾal-ʿulūm), of which a second, more literal translationwas produced by Gerard of Cremona. But it was Gundisalvi’s ownArabicized treatise which was the main channel ofal-Fārābī’s influence. The mostly anonymousintroductory literature forartes students of the thirteenthcentury draws amply on Gundisalvi’s treatise, sometimesreferring to Gundisalvi as “Alpharabius” (Lafleur 1988,341n). The translator Michael Scot also writes his own Division ofphilosophy, in which he adopts substantial material from Gundisalvi,but arranges it according to his own scheme (Burnett 1997).

Gundisalvi adopts central principles for the division of the sciencesfrom Avicenna: that the principal criterion of division between thesciences is their subject matter; that a science cannot demonstratethe existence of its own subject matter; and that there are two kindsof subordination of a science: either as a part (pars) ofanother science, when it studies a part of its subject matter, or as aspecies (species) of another science, when it studies thesubject matter in a specific respect (Hugonnard-Roche 1984;Fidora & Werner 2007, 24–35).

Al-Fārābī’s influence is particularly obvious inthe enumeration of the seven parts of grammar, the eight parts ofnatural science (covering the spectrum of Aristotle’slibrinaturales), and the seven parts of mathematics: arithmetic,music, geometry, optics, astrology, astronomy, the science of weights,the science of technical devices (ingenia) (see the tables inBouyges 1923, 65–69). As to the discipline of logic, Gundisalviexplicitly embraces al-Fārābī’s division intoeight parts, following the tradition which makes Aristotle’sRhetoric andPoetic parts of logic. The Farabiandivision of logic into eight parts reappears, for example, in RogerBacon (Maierù 1987) and in Arnoul de Provence’sDivision of the Sciences (ca. 1250); Arnoul remarks thatneither Aristotle nor common usage includesRhetoric andPoetic among the parts of logic (Lafleur 1988, 342).Gundisalvi further distinguishes with al-Fārābī betweenfive kinds of syllogistic reasoning, of which demonstration is thehighest. Al-Fārābī’s emphasis on demonstration asthe pivotal means for the acquisition of certain knowledge is animportant innovation of Arabic philosophy, which reached the LatinWest via Gundisalvi (Fidora 2007).

The influence of al-Fārābī’sEnumeration ofthe Sciences extends also to specific areas such as music (Farmer1934, 31–34). In general, al-Fārābī’s andGundisalvi’s works were instrumental in disseminating asystematic division of the sciences which integrated the full range ofAristotle’s works and a broad spectrum of sciences, many ofwhich were new to the Latin West (Burnett 2011).

3. Logic

The Arabic influence in logic is thinner than in other disciplines(apart from ethics), because only a few works of Arabic logic weretranslated into Latin. The most influential translations were theIsagoge part of Avicenna’s summaThe Healing(al-Shifāʾ) and al-Ghazālī’sIntentions of the Philosophers, the first part of which is areworking of Avicennian logic. Ramón Llull produced an Arabiccompendium of al-Ghazālī’s text, which he himselftranslated into Latin (Lohr 1965). To these sources one may addal-Fārābī’sEnumeration of the Sciences,which transmitted much material on logical disciplines. HermannusAlemannus’ translation of Averroes’ commentary on thePoetics was important because it remained the only source onAristotelian poetics available in the Middle Ages and had a richmanuscript transmission (for its influence on Petrarch’snegative judgement about Arabic poetry see Burnett 1997). Othertranslated texts remained largely uninfluential, such as William ofLuna’s translations of five commentaries by Averroes onAristotle’s logical works, or the Averroes translations madefrom Hebrew in the Renaissance. In sum, this means that the Latin Westwas not aware of the more innovative parts of Arabic logic, such as insyllogistics and modal logic (Street 2005).

Several particular doctrines of Arabic logic, however, were veryinfluential. Among them was Avicenna’s theory of the subjectmatter of logic, with its related doctrine of first and secondintentions. Avicenna’s basic claim is that logic deals withsecond-order concepts. This is discussed in the logic part ofTheHealing, but spelled out in technical vocabulary in themetaphysics part (Metaphysics I,2): “The subject matterof logic is the secondary intelligible concepts(al-maʿānī al-maʿqūlaal-thāniyya,intentiones intellectae secundo),which depend on the primary intelligible concepts with respect to themanner by which one arrives through them at the unknown from theknown”. In this sentence, “concept”(maʿnan) is rendered in Latin with the termintentio.

A brief note on this term is at place: In Arabic-Latin translationliterature,intentio is very often used to renderma´nan, with the consequence that the termintentio took on a similarly broad semantic range as itsArabic counterpart. In the writings of Avicenna,maʿnanmay mean “concept”, but also “meaning” of aword, or something “intelligible” by the intellect, or“perceptible” by estimation but not by the external senses(on estimation see section 5.1). In Averroes’ epistemology, thetermmaʿnan has a specific meaning as the object ofmemory and a broader meaning as the abstracted content of sensory,imaginative or intelligible forms (Black 1996, 166).

In Avicenna’s theory of logic, second intentions are defined asthe properties of concepts which these concepts acquire when used inattaining knowledge, for example: being a subject or being apredicate, being a premise or being a syllogism. Avicenna thusconfirms that logic has a proper subject matter, and hence becomes afull-fledged part of philosophy, and not only a tool for thephilosophical disciplines (Sabra 1980, 752–753).Avicenna’s definition of logic appears already in DominicusGundisalvi (De divisione philosophiae 150). Further Latinwriters to adopt Avicenna’s thesis that the subject matter oflogic is second intentions are Roger Bacon and Thomas Aquinas,followed by many subsequent authors such as Pseudo-Robert Kilwardby,Radulphus Brito, Hervaeus Natalis, Peter Aureoli, Duns Scotus andWilliam of Ockham (Knudsen 1982; Maierù 1987; Perler 1994).

It was a matter of dispute how first and second intentions differ,what they refer to and what their ontological status is, a disputebordering on epistemology and the philosophy of mind. Importantparticipants in this discussion are Roger Bacon, who definesintentions as intelligible species, that is, mental likenesses ofthings, and Hervaeus Natalis and Peter Aureoli, who (apart fromdisagreeing on many issues) both hold that intentions are neitheridentical with extramental things nor with qualities of the intellect;they have their own “intentional being” (esseintentionale), which is the result of a cognitive act (Perler1994). This position was criticized both by nominalists and realists:the nominalist William of Ockham objected against the reification ofintentions and held that intentions are always natural signs in themind; second intentions are natural signs which signify other naturalsigns (Summa logicae I.12); the realist author Walter Burleyrejects the idea of a special being of intentions and argues thatsecond intentions are part of extramental reality (Knudsen 1982).Logic as the science of second intentions continued to be aphilosophical topic well into the sixteenth century, especially amongThomists and Scotist authors.

4. Natural Philosophy

Natural philosophy is the field with the greatest number ofArabic-Latin translations. In this discipline, Arabic philosophers hadbeen particularly active, and Latin philosophers were particularlyinterested. Arabic natural philosophy reached the Latin West earlierthan the other philosophical disciplines. The medical and astrologicaltranslations of the late eleventh and early twelfth centurytransported much philosophical material of the Graeco-Arabic traditionto the Latin world. Under the influence of these Arabic sources, Latinauthors of the twelfth century explained natural phenomena by recourseto the four elements, the four qualities, the four humours, the threespiritus (natural, spiritual, animal) and their organs, thelocalization of the soul’s faculties in different cavities ofthe brain, the distinction between the sublunar and the heavenlyuniverse, the circular movement of the heavenly spheres, and by usingAristotelian concepts such as matter and form, action and passion,cause and effect. While many Latin writers of the twelfth centurycontinued to understand nature in terms of the Latin Christiantradition, others, in the context of the so-called “school ofChartres”, such as William of Conches, Adelard of Bath, Hermannof Carinthia and Bernardus Silvestris, drew amply on the new medicaland astrological sources, often combining them with the doctrines ofPlato’sTimaeus (Burnett 1982, introduction; cf. alsoLemay 1962). Sometimes they did this by openly dividing theirpresentation into a section according to the church fathers and asection according to the philosophers and natural scientists(physici), which integrated material from the Latin andArabic philosophical traditions (e.g. the treatisesPhilosophia by William of Conches andDe natura corporiset animae by William of St.-Thierry).

The influence of Arabic in natural philosophy in the later MiddleAges, that is, after the translations of Avicenna and Averroes, isparticularly strong in psychology (section 5 below). But otherdisciplines, such as physics, cosmology, meteorology, or zoology, arealso influenced by Arabic sources (see Mandosio 2018 on meteorology),in particular by Averroes’ commentaries and by his criticisms ofAvicenna (listed in Cerami 2018). Several theses from Averroes’long commentaries onPhysics andDe caelo influencedthe history of medieval Latin physics and cosmology: the explanationof projectile motion (e.g. of a thrown stone) as the successive motionof the medium; the thesis that motion and time differ in reality, butonly with respect to the numbering soul; and the theory that theheavenly sphere is in a place only accidentally, insofar as it movesaround the earth at its center (Maier 1951; Wood 2010; Trifogli 2000;Trifogli 2010).

One issue on which Avicenna and Averroes disagreed was the “formof bodiliness” (ṣūra jismiyya,formacorporeitatis), which, Avicenna argued, is the common form ofprime matter that underlies all individual bodily forms, whereasAverroes denied that the “form of corporeality” is a formin the category of substance; it is only an accident, to be identifiedwith indeterminate three-dimensionality (Hyman 1965). Thomas Aquinasrejected the idea that prior to the intellective soul there exists asubstantial form in matter (Summa theol. Ia q. 76 a. 4, a.6). The Avicennian concept was adopted by others, such as Henry ofGhent and Duns Scotus, and thus served the theory of the plurality ofsubstantial forms. That prime matter has its own actuality became aprinciple identifying the Franciscan party in the doctrinal struggleswith the Dominicans. The discussion of the concept offormacorporeitatis continued well into the sixteenth century (DesChene 2000, 81–93).

Three prominent topics of natural philosophy are here singled out forcloser treatment: the eternity of the world, the persistence ofelements in a compound and spontaneous generation.

4.1 Eternity of the World

The Greek theory of the eternity of the world was a challenge to theChristian world view, a challenge increased by the fact that thetheory was supported by Arabic sources: by Avicenna, who combined itwith a metaphysical concept of God as the “necessary being initself”, which is the eternal efficient cause of the existenceof the heavenly and sublunar world (see section 6.4 on the firstcause), and by Averroes, who combined it with a conception of God asthe prime mover, whose existence is proved in natural philosophy. InGiles of Rome’Errors of the Philosophers, Avicenna andAverroes are accused of many “errors”, but the eternity ofthe world figures most prominently. Averroes, in particular, isattacked for opposing “even more vehemently than did thePhilosopher (Aristotle) those who held that the world had had abeginning” (Giles of Rome 1944, 15). The eternity of the worldand related theses were condemned as heretical in 1270 and 1277 by theParisian bishop Étienne Tempier (art. 87, 90, 99, 184)(Piché 1999).

In the thirteenth century and beyond, the issue was widely discussedby the scholastics, who arrived at a variety of positions, butunanimously held that the world was created in time by God, whichmeans that they never fully shared Avicenna’s or Averroes’position. Many arguments of the scholastic discussion were drawn fromArabic authorities, in particular from Averroes’ longcommentaries onDe caelo andPhysics and fromAvicenna’sMetaphysics. First traces of Arabicinfluence can be found in Philip the Chancellor’sSumma debono (dating 1225–8). Thomas of York, for instance, takesover Averroes’ exposition of the four principal views on theissue (Comm. magnum De caelo I.102; Dales 1990, 81). Passagesdrawn from Arabic texts were not only employed to defend, but also toattack the eternity thesis. One particularly often quoted argumentcomes from al-Ghazālī’sIntentions of thePhilosophers: If the world was eternal, an infinite number of(immortal) souls would now exist, which is impossible (Dales 1990, 44,256). Another very influential source of the Latin debate wasMaimonides’Guideforthe Perplexed(II.13–28); Maimonides argued that both eternity andnon-eternity are possible philosophically.

Thomas Aquinas’Commentary on the Sentences (II, d.1q.1 a.5) is a good example of the impact of Arabic sources. Among thearguments cited from Averroes in favour of eternity are that there isalways another moment in time before a moment in time; that onlymotion can be the cause of a change from rest to motion; that if theworld had a beginning, a vacuum would precede the world (Comm.magnum De caelo III.29,Comm. magnum Phys.VIII.8,9,11,15). Avicenna is cited by Thomas as holding thatGod’s will is unchangeable and never starts anew (an argumentadvanced also by Averroes), and that it is impossible that Godprecedes the world in duration, because this implies that time existedbefore the world and before movement (Metaphysics IX.1).These arguments clearly influenced Thomas’ conclusion that theeternity thesis is the most probable in philosophical terms. However,just like creation, eternity escapes full demonstration. From thestandpoint of faith, the eternity of the world is false and heretical.In his treatiseOn the Eternity of the World, Thomas Aquinas,in contrast to most of his contemporaries, defends the possibility ofan eternal creation, thus approaching the position of Avicenna andother Neoplatonic thinkers.

Positions on the eternity of the world by some masters of arts were insome cases very provocative. In the eyes of Siger of Brabant, thenatural philosopher cannot but conclude that the world is eternallycreated, whereas the metaphysician concedes that God’s will isinscrutable and that hence there is no certainty about eternity ornon-eternity (De aeternitate mundi; Quaest. in tertium Deanima q.2). For Boethius of Dacia, the natural philosopher has toinfer the eternity of movement from the principles of naturalphilosophy, but the metaphysician, even though he can demonstrate theexistence of a first cause, is unable to demonstrate whether the worldis coeternal with the first cause or non-eternal, given theinscrutability of God’s will (De aeternitate mundi).Both authors share the conviction that the natural philosopher isforced to conclude that the world is eternal, thus provokingtheological opposition. The arguments for this conclusion were largelyfurnished by Arabic sources.

4.2 The Elements in a Compound

In the Latin West, Avicenna and Averroes were known as the principaladversaries on a much-discussed question of element theory, especiallyin the fourteenth century. Given that all physical substances (apartfrom the elements themselves) are mixtures of elements, how do theelements exist in them? (Maier 1952; Grant 1974, §77, Eichner2005, 139–145). Avicenna’s answer is that the substantialforms of the elements remain unaltered when a compound is formed; onlythe qualities of the elements are altered and unite to a mean quality(qualitas media), or complexion (complexio). Thecomplexion disposes the matter to receive the substantial form of thecompound from the active intellect, the giver of forms (datorformarum) (The Healing: Physics I.10,Ongeneration 6). The problem with this position, as manyscholastics saw, is that several bodies are combined in one, which donot form a true mixture. Averroes rejects Avicenna’s theory andargues that the substantial forms of the elements are diminished inthe compound (Comm. magnum De caelo III.67). The form of thecompound is “composed” of the elementary forms (Comm.magnum Metaph. XII.22). In order not to violate Aristotle’sprinciple that substantial forms cannot be diminished or augmented (aman is not more man than another), Averroes argued that elementaryforms are not substantial forms in the full sense.

A third influential alternative was proposed by Thomas Aquinas. Thomasargued that the substantial forms of the elements are destroyed andthat only the qualities contribute to the mixture. Thomas sharesAvicenna’s conviction that every form presupposes a certainmaterial disposition, which is the mean quality characteristic of thecompound. But he deviates from Avicenna in that the forms of theelements are not preserved; they are only virtually present in thecompound, in that their powers survive (De mixtioneelementorum, cf.Summa theol. Ia q. 76 a. 4).Thomas’ position found many adherents. Its problem is thatphysical bodies cannot truly be called mixtures of elements.

Avicenna’s theory of the permanence of substantial forms wasoften mentioned, but rarely accepted in the Latin West.Averroes’ position, that the elementary forms can be diminishedand augmented, found many supporters, among them Henry of Ghent,Petrus Johannes Olivi, Richard of Middleton, John of Jandun andseveral members of the Merton school of the fourteenth century (Maier1952, 36–46). Many authors accept Averroes’ position withmodifications, especially by reinterpreting the thesis of theintension and remission of elementary forms. Henry Bate and Dietrichof Freiberg argue that the diminished forms assume the character ofpotential forms and thus join the matter of the compound; the form ofthe compound is a form added to these diminished forms. For Averroes,in contrast, the combination of the diminished forms was identicalwith the new form of the compound. In the Renaissance, the issuecontinued to be discussed. There was disagreement even among thefollowers of Averroes. Some, as Marcantonio Zimara, held that the formof the compound was added to the other forms, others, as JacopoZabarella, argued against such addition (Maier 1952, 46–69).

4.3 Spontaneous Generation

Spontaneous generation, that is, the generation of life without theirbeing any parents, as when worms grow in decay, is a much discussedissue of medieval physics and metaphysics. The conflictingexplanations of the phenomenon by Avicenna and Averroes muchdetermined the Latin discussion until the sixteenth century. WhileAvicenna holds that spontaneous generation depends upon ever morerefined mixtures of elementary qualities which trigger the emanationof forms from the active intellect, the giver of forms (TheHealing: Meteorology II.6:On Floods), Averroes explainsit with the influence of certain celestial constellations whichactualize potential forms in water or earth. Avicenna and Averroesalso disagree about the special case of the spontaneous generation ofhuman beings, which Avicenna finds possible, whereas Averroes doesnot. For Averroes, all spontaneously created animals are not true, butabnormal, monstrous animals (Comm. magnum Metaph. II.15,VII.31, XII.13,18) (Bertolacci 2013a).

In the Latin West, Averroes’ explanation dominated thediscussion for several centuries (Hasse 2007a). Thomas Aquinas argues that there isno need to assume the existence of an Avicennian giver of forms toexplain spontaneous generation, since the celestial power suffices forproducing ordinary animals from matter. More complex beings, however,such as horses and human beings, cannot be produced by the celestialpower alone without the formative power of the semen (Quaest. depotentia, qu. 3 a. 8,9,11). Thomas’ position was called themedia via by later authors, that is, the middle way betweenAvicenna and Averroes, since Thomas rejected Avicenna’s theory,but also modified Averroes’ position in treating spontaneousgeneration as a natural, and not a miraculous phenomenon.

Averroes’ theory of celestial influence and ThomasAquinas’media via became mainstream in the Latinmiddle ages. A few authors, however, followed Avicenna in allowing forthe spontaneous generation of human beings, among them AlbertusMagnus, Blasius of Parma, and, in the Renaissance, Pietro Pomponazzi,Paolo Ricci and Tiberio Russiliano. Pomponazzi makes the spontaneousgeneration of human beings dependent upon the conjunction of thesuperior planets Jupiter and Saturn, and thus introduces anotherArabic theory into the discussion: Albumasar’s astrologicaltheory of the great conjunctions (Nardi 1965).

A modified version of Avicenna’s theory of the giver of formsappears in John Buridan, who deviates from the dominant position thatthe form of human beings comes from without, i.e. from God, whereasthat of animals is educed from matter. In contrast, Buridan holds thatall forms are given by a separate incorporeal substance,which he calls God. The phenomenon of spontaneous generation supportsthis view, since it cannot be explained with the influence of thestars, which is too weak and imperfect to generate animals (InMetaphysicen Aristotelis lib. 8 q. 9). What does not appear inBuridan, is Avicenna’s theory of the subsequent mixtures ofelementary qualities.

5. Psychology

In Latin psychology, the influence of Arabic works is particularlystrong and lasted well into the sixteenth century. Avicenna andAverroes, the most influential philosophers, presented the West with afaculty psychology in the tradition of Aristotle and enriched byGraeco-Arabic medical doctrines, such as about the cavities of thebrain, the nerves, and the spirits which transport information in thebody. From about 1220 onwards, the full range of Avicennian faculties(vegetative, external and internal senses, the motive faculties,practical and theoretical intellect) appears in Latin treatises bymasters of arts and theologians. This system of faculties remains, byand large, standard for a long time in philosophical handbooks, fromthe anonymousPhilosophy of the Simple (Philosophiapauperum) and Vincent of Beauvais’Mirror ofNature (Speculum naturale) in the thirteenth century upto thePhilosophic Pearl (Margarita philosophica) ofthe 1490s. Also influential was Avicenna’s definition of thesoul as a separate substance (Hasse 2008) and his thought experiment of the“Flying Man” (Hasse 2000, 80–92).

Averroes disagreed with Avicenna on a number of topics concerningfaculty psychology, for example: on the organ and medium of touch, onthe material or immaterial transmission of odors, and on whether humanbeings have an estimative faculty or not. These controversies werecontinued in the Latin tradition. The most influential pieces ofpsychological doctrine imported from the Arabs probably wereAvicenna’s theory of estimation (wahm), his theory ofpotential, acquired and active intellects, and Averroes’ thesisthat there is one intellect for all human beings.

5.1 Estimation

Avicenna had argued in hisOn the Soul (theDe animapart ofThe Healing I.5 and IV.3) that human beings andanimals share an internal sense called estimation (wahm,aestimatio), which perceives so-called“intentions” (maʿānin,intentiones) in an object, such as hostility andfriendliness: The sheep perceives hostility in the wolf and judgesthat the wolf is to be fled from. The basic ingredients of this theorywere adopted by many scholastic writers. There was disagreement,however, over several issues: Firstly, Averroes and Thomas Aquinas (incontrast to Avicenna, Albertus Magnus and others) argued thatestimation existed in animals only, but not in human beings. Toexplain instinctive reactions in human beings, it is not necessary,they argue, to assume the existence of a faculty besides thecogitative faculty, orratio particularis, as Thomas calls it(Summa theologiae Ia 81.3c). Secondly, scholastic writerswere divided over whether the intentions are perceived in the object,as Avicenna and Thomas Aquinas say (cf. also John Blund,Tractatusde anima, ch. 19), or abstracted from sensory forms, as forinstance Albertus Magnus and John Buridan argue (Albertus,Deanima II.4.7; Buridan,Quaestiones de anima II.22)(Black 2000; Hasse 2000, 141–153; cf. also Black 2011). Thirdly,there was disagreement about the notion of “animaljudgement” propagated by Avicenna. Nominalists such as AdamWodeham argue that judgements always involve the formation of acomplex sentence, which presupposes linguistic capabilities; animals,therefore, never truly judge (Perler 2006).

5.2 Active Intellect

Typical for Arabic intellect theory is the distinction between severaldegrees or levels of intellect, from an entirely potential intellectup to a perpetually active intellect, and the assumption, taken overfrom later Greek philosophers, that the active intellect is an entityseparate from the human being. Al-Fārābī, Avicenna andAverroes identify the active intellect with the lowest of thecosmological intelligences, and argue that the human intellect is ableto conjoin with the active intellect. The great majority of scholasticwriters teach that potential and active intellect are parts of thesoul, but there also existed a current adopting the Arabic idea of aseparate active intellect (e.g. Dominicus Gundisalvi and PetrusHispanus). Several scholastic authors identify the active intellectwith God on the authority of Avicenna and Augustine – a positionwhich modern scholars have labeled “Augustinismeavicennisant” (Gilson 1926/27, 102). Among the earliestexponents of the doctrine is Jean de la Rochelle, whose psychologicalworks were written in the 1230s. He teaches that the term“active intellect” refers either to God or to theangels’ intellect or to the internal light of human beings,depending upon which intellectual objects are grasped by the humanintellect (Summa de anima 116). This doctrine reappears inthe 1240s in theSumma fratris Alexandri, and in Vincent ofBeauvais. Later adherents are Roger Bacon, John Pecham, Roger Marston,Vital du Four, and also Henry of Ghent (though only in parts of hiswork). But other scholastics disagree. Adam of Buckfield, Bonaventureand Thomas Aquinas criticize unnamed theologians for identifying theactive intellect with God. As philological evidence shows, they referto the above-mentioned current which begins with Jean de laRochelle. Thomas rejects the thesis because he interprets it inilluminationist terms and finds it incompatible with his ownepistemology of abstraction (Summa contra gentilesII.74). One should note, however, that Avicenna’s epistemologycombines both abstractionist and emanationist aspects and that histheory of abstraction also attracted Latin readers (Hasse 2001, butcf. McGinnis 2007, and Black 2014).

5.3 The Four Intellects

Avicenna distinguishes four different states of the human intellect,which are not different faculties of the soul, but different phases ofintellection: three potential intellects, called material,inhabitu,in effectu, and one actually thinking intellect,the “acquired intellect” (al-ʿaqlal-mustafād,intellectus adeptus). The firstpotential intellect is pure potentiality to know anything; the secondpotential intellect knows axioms such as “The whole is biggerthan the part”; the third has already acquired conclusionsthrough syllogistic reasoning and the intuition of middle terms, butdoes not consider them at the moment; the “acquiredintellect” comes about when the human intellect connects withthe active intellect (De anima I.5). This theory exerted aprofound influence on scholastic intellect theory, especially in theperiod from Dominicus Gundisalvi to Albertus Magnus. The scholasticsinherited from Avicenna the principal idea that the activity of thehuman intellect can be differentiated into different phases of gradualdevelopment and into different acts of syllogistic reasoning (Hasse2000, ch. II.6).

An important step in the reception of the doctrine is the anonymoustreatiseDe anima et de potentiis eius by a Parisian masterof arts of ca. 1225 (Gauthier 1982a, 53). This author adopts fromAvicenna the first three levels of intellect, the first being purepotentiality, the second knowing first propositions, the thirdconclusions, and combines it with teachings from Aristotle’sPosterior Analytics (I.3 and II.19) about the intellectknowing axioms and principles. Jean de la Rochelle continues this lineand calls the second intellectintellectus principiorum, thethirdintellectus conclusionum, and uses a Boethian term forthe axioms of the second intellect: “common notion of themind” (communis animi conceptio), thus combining theAvicennian doctrine with Latin axiomatic theory (Tractatus dedivisione multiplici potentiarum animae II.18).

In the writings of Albertus Magnus, the influence of Avicenna iscombined with that of Averroes, who distinguishes two intellects apartfrom the separate active intellect: the material intellect, which ispure potentiality (and unique, see section 5.4 below) and thespeculative intellect, which is the actuality of the graspedintelligible. Averroes and Avicenna both teach that the human andactive intellect conjoin in the moment of intellection. Averroes, inparticular, claims that a perfect conjunction with the activeintellect results in God-like knowledge and that such a conjunction ispossible in this life (Comm. magnum De anima III.5 andIII.36).

Albertus Magnus, in his earlyDe homine (qu. 56 a. 3), adoptsthe Avicennian doctrine of three potential intellects in hisscholastic reformulation, but in his later works, under the influenceof Averroes, transforms it into a theory of intellectual ascension.The highest level of the human intellect is called “acquiredintellect” (intellectus adeptus) and results from theconjunction between the potential and the active intellect, both partsof the human soul. In this stage, the intellect is able to grasp allintellectual knowledge, and does not need to have recourse to thesenses again. In virtue of this intellect, a human being becomesGod-like (De anima 3.3.11) (deLibera 2005, 325–327). Thomas Aquinas sharply disagrees. Theintellect can never dispense with the senses, since it needs thephantasms for conceiving an intellectual form. This is why perfectintellectual knowledge is not possible in this life (Summatheol. Ia q. 84 a. 7).

5.4 Averroes’ Unicity Thesis

Averroes’ best known philosophical doctrine holds that there isonly one intellect for all human beings. The doctrine is sometimeslabelled “monopsychism”, but this is a problematic term,since Averroes’ unicity thesis concerns the intellect, not thesoul. Averroes’ theory has an epistemological and an ontologicalpurpose. On the one hand, Averroes wants to explain how universalintelligibles can be known, on the other hand, he wants to account forAristotle’s claim that the intellect is pure potentiality andunmixed with the body (Comm. magnum De anima III.5). Manyscholastic readers were troubled by the problem of whether thematerial (or potential) intellect, if it is one, can be the form ofthe body. This problem was not directly addressed by Averroes himself,but by many of his Latin partisans.

Modern scholarship is still divided about the significance of thecurrent of Averroism in the thirteenth century (for the more recentdiscussion see Imbach 1991; Hayoun/de Libera 1991; Bianchi 1993;Niewöhner/Sturlese 1994; Kuksewicz 1997; Brenet 2003,21–22; Coccia 2005, 20–53; Hasse 2007b; Martin 2007; Calma2010, 11–20, 367–373; Martin 2013; Akasoy & Giglioni 2013).It was argued, for instance, that the “radicalAristotelians” of the thirteenth century were not“Averroists” in a strict sense (Van Steenberghen 1974,531–534). But that much is clear: there existed at least fourgroups of authors who explicitly adopted the unicity thesis in one oftheir writings: Siger of Brabant and possibly other masters of arts inlater thirteenth-century Paris; a second Parisian group in the earlyfourteenth century around Thomas Wilton, John of Jandun and JohnBaconthorpe; several Italian masters of arts at Bologna university inthe fourteenth century; and a larger group of authors in RenaissanceItaly and especially in Padua.

When the medievals used the Latin termaverroista, theyreferred to authors belonging to these groups. The termaverroista came into use in the later thirteenth century, buton rare occasions. The first appearance, as we can see today, is inThomas Aquinas’ treatiseOn the Unicity of theIntellect (De unitate intellectus). The additional titlephrasecontra averroistas appears only in the latermanuscript tradition and is unlikely to be authentic. It was in thedecades around 1500 that the term was used most frequently.Averroistae were associated mainly with the unicity thesis,but also with theories about the eternity of the world, God’sknowledge of the world, prime matter and happiness (Kuksewicz 1997,93–96; Calma 2010). In theRenaissance,averroista was also used, with a positiveconnotation, to refer to experts on Averroes (Martin 2007; Martin2013). A sensible historiographical usage of the term“Averroism” should be tied to the medieval and Renaissanceusages. In particular, two senses of the term “Averroism”seem historically legitimate: as meaning a current of followers ofAverroes who hold theologically controversional doctrines, or asmeaning a current of experts on Averroes. The first sense has a longertradition in the Middle Ages and in modern scholarship and istherefore to be preferred generally. Some modern historians use theterm “Averroism” in a much broader sense for allinfluences of Averroes’ thought (e.g. Gauthier 1982,334–335; Calma 2010, 368–369); so-called“Averroisms” would then be found, for instance, in almostall Latin Aristotle commentaries of the later Middle Ages. This usage,however, ignores the historical roots of the meaning of the term.

Siger of Brabant (d. 1284) and John of Jandun (d. 1328) were the bestknown and most influential Averroists. Siger, in his first and mostexplicitly Averroistic work on the soul, argues that the separate andeternal intellect is united to the body only in an operational unionand that the true form of the body is the sensitive soul (Quaest.in tertium de anima, esp. q. 3 and 9). Under the influence ofThomas Aquinas and others, Siger later revised his position. For Johnof Jandun, the intellective soul, which in itself is one and separate,operates within the body. It is united to the body only through theassistance of the phantasmata (Brenet 2003). The RenaissanceAverroists Agostino Nifo and Luca Prassicio argued that Siger and Johnof Jandun professed conflicting views: they interpreted Siger asholding that the unique intellect can be united to the body as formand John of Jandun that it cannot. Another influential Averroist wasJohn Baconthorpe (d. 1345/48): He developed the theory of theso-called “double conjunction” (copulatiobifaria) between intellect and bodily phantasms: oneepistemological, one ontological. The ontological conjunctionpresupposes a union of unique intellect and human being in a way thatthe intellect becomes a human faculty (Etzwiler 1971, 266–269).Among the most explicit and outspoken Averroists of the Renaissancewere Nicoletto Vernia (d. 1499) and Luca Prassicio (d. 1533). Theunicity thesis was successful among Latin authors not only becauseAverroes asthe commentator had become an exceptionalauthority of university education, but also because it was attractivephilosophically: it explained the possibility of the knowledge ofuniversals and it ensured that the intellective soul, as demanded byAristotle (De anima III.4, 429a22–25), was not mixedwith the body.

The unicity thesis was included among the doctrines condemned in 1270and 1277 in Paris (art. 32) and in 1489 in Padua by the local bishops.From a theological vantage point, its main drawback was its conflictwith the doctrine of individual immortality. The principalphilosophical counter-argument, first presented by Averroes himself(Comm. magnum De anima, 393) and powerfully formulated byThomas Aquinas, was that the unicity thesis could not account for thefact that “this individual man thinks”, as Thomas puts it(“hic homo singularis intelligit”,De unitateintellectus III) (Black 2004). The standard reply by Averroes andhis followers was that the intelligible form is joined to theindividual human being through the actualized imaginative form, whichis particular. This way, individual knowledge of universal forms ispossible.

The decades around 1500 saw the high tide of the Averroist current, asfar as we can discern today (Schmitt 1979; Akasoy & Giglioni2013). This is indicated by several pieces of evidence: the frequentusage of the termaverroista; the significant number ofauthors who adopt the unicity thesis in one of their works; thecomposition of super-commentaries on Averroes’ commentaries;and, finally, the fact that the correct interpretation ofAverroes’ philosophical position became a matter of disputeamong his partisans (e.g. between Nifo, Trombetta, Zimara, Pomponazziand Prassicio). The unicity thesis lost its appeal as late as in themiddle of the sixteenth century, with the advent of new trends ofAristotelianism that gave alternative explanations of universalintellection (e.g. by Melanchthon, Zabarella and Suarez) (Hasse 2016,ch. 5).

5.5 Naturalistic Theories of Prophecy

The philosophical interpretation of prophecy and miracles is a typicalfeature of Arabic philosophy. The Latin West was not acquainted withal-Fārābī’s concept of the philosopher-prophet,the leader of the excellent city, but with parts ofal-Kindī’s and Avicenna’s theories. The general lineof Avicenna’s naturalistic theory of prophecy, which describesprophecy as resulting from extraordinary faculties of the soul, wascriticized by Thomas Aquinas. Thomas admits that there is also“natural prophecy” which results from the contact of humanimagination and intellect with the celestial bodies and angels, but“divine prophecy” is entirely dependent upon God, and notupon the preparedness of the human soul (Quaest. de veritate,q. 12, a. 1 and 3).

Among the specifics of prophecy theory, the working of miraclesreceived most attention in the Latin West. al-Kindī’s andAvicenna’s explanation of miracles is naturalistic in the sensethat neither theory involves divine factors. al-Kindī argues inOn Rays (De radiis, extant only in Latin) that if aperson conceives a corporeal image in his imagination, the imageassumes a material existence in thespiritus that belongs tothe faculty. Thespiritus in turn sends out rays, which alterobjects in the external world (d’Alverny & Hudry 1975,230–1). An alternative to this extramission theory is formulatedby Avicenna, who claims that persons who have perfected their body andsoul are able to affect directly the external matter of the world andmay produce rain, fertile seasons, and the like – by sheer powerof the will. Avicenna arrives at this conclusion by generalizing theprinciple that there are psychic causes for material effects (Deanima IV.4).

Albertus Magnus rejects Avicenna’s long-distance theory becauseit breaks with the Aristotelian rule that there is no efficientcausation without material contact (De sensu et sensato1.10). Thomas Aquinas follows a third alternative: that psychic powerscan move the intervening medium, and so indirectly act on externalobjects, which explains the damage caused by an evil eye. Thomasborrows from a passage in Aristotle’sOn Dreams, inwhich air is moved and affected by the eyes of menstruating women(459b23–60a24). True miracles, however, are always produced byGod (Summa theol. Ia q.117 a. 3). In the later Middle Ages,the Aristotelian theory of the movable medium proved more successfulthan the extramission and action-at-a-distance theories ofal-Kindī and Avicenna. An exception is Roger Bacon, who teachesthat some persons are able to send out “powers, forms, andheat” in order to alter bodies outside. Bacon employsal-Kindī’s theory of extramission in order to explain magicas a purely natural phenomenon (inDe secretis operibus artis etnaturae).

The high time for Arabic theories of miracles came in the Renaissance(Hasse 2007c, 121–125). Marsilio Ficino in hisPlatonicTheology (Theologia platonica XIII.4.8–9) explainslong-distance effects such as the evil eye with an extramission modelreminiscent of al-Kindī: The evil eye is explained with vaporsbeing emitted from the sorcerer’s eyes which reach and afflictthe victim. True miracles, however, cannot be achieved withoutGod’s assistence. Andrea Cattani (d. 1506) explicitly adoptsAvicenna’s theory that noble souls are able to influence theexternal world without mediation, but ties this extraordinary capacityto inspiration by the Holy Ghost. Such reservations do not appear inadoption of the theory by Pietro Bairo (d. 1558). Pietro Pomponazzi(d. 1525) discusses Avicenna’s position, but favours anextramission theory: He explains a contemporary miracle in the town ofAquila with the transmission of vapors which are issued from the eyesof the observers (inDe naturalium effectuum causis sive deincantationibus, 237–8).

6. Metaphysics

The two most important Arabic sources of medieval Latin metaphysicsare the metaphysics part (Ilāhiyyāt) ofAvicenna’s philosophical summaThe Healing(al-Shifāʾ), here referred to as hisMetaphysics (Hasse & Bertolacci 2012) and Averroes’Long Commentary on the Metaphysics (Bertolacci 2009).Avicenna’s treatise presented metaphysics as a fully systematicdiscipline and combined Aristotelian and Neoplatonic traditions.Averroes’ commentary proved an indispensable tool forunderstanding Aristotle’s text and offered an alternative toAvicenna’s position on several important issues.Al-Ghazālī’sIntentions of the Philosophersalso contributed much to the dissemination of Avicennian metaphysicsin the Latin West (Minnema 2014; Minnema 2017). Another veryinfluential text was theDiscourse on the Pure Good (Kalāmfī maḥḍ al-khayr,Liber de purabonitate), known in Latin also asThe Book of Causes (Liberde causis). The anonymous Arabic author of the treatiserearranged passages from Proclus’Elements of Theologyfrom a monotheistic, creationist and Plotinian perspective, andcombined them with doctrines from Plotinian and Aristotelian sources.In 1255, the Latin text became part of the required curriculum ofstudy in the Faculty of Arts in Paris, together with the works ofAristotle, with the effect that the text received many commentariesand enjoyed an extraordinary transmission in more than 237 manuscripts(Taylor 1983). TheLiber de causis was long considered to bean authentic text by Aristotle. When William of Moerbeke in 1268translated Proclus’Elements of Theology into Latin,Thomas Aquinas was able to identify Proclus as the main source of thetext. TheLiber de causis remained popular, however. At least74 commentaries from the twelfth to fifteenth centuries testify to itsgreat influence (d’Ancona Costa 1995, 195–258;Fidora/Niederberger 2001, 205–247; Calma 2016, I,20–21).

6.1 The Subject of Metaphysics

It was well known among the scholastics that Avicenna and Averroesdisagreed about the subject matter of metaphysics. In the two openingchapters of hisMetaphysics, Avicenna argues that no sciencecan demonstrate the existence of its proper subject, and that henceGod, whose existence is proven in metaphysics, cannot be its propersubject. The subject (mawḍūʿ, subiectum) ofmetaphysics is being as being. What is sought after(maṭlūb,quaesitum) in metaphysics, isthat which unconditionally accompanies being: such as the causes ofbeing, among which God is the first. Averroes countered that theexistence of the first principle cannot be demonstrated inmetaphysics, since such a proof can only begin with God’seffects and with movement in particular. This is why the proof of Godbelongs to physics. The subject matter of metaphysics is separablebeings, among which counts God, as Averroes argues in theLongCommentary on the Physics (ch. I.83, but in other works heassigns this function to being as being; see Bertolacci 2007).

Most scholastic authors favoured Avicenna’s position overAverroes’s, but within this mainstream position there wasdisagreement about the manner in which God relates to the subject ofmetaphysics, being as being. Albertus Magnus defends Avicenna againstAverroes’ criticism. Being as being is the subject ofmetaphysics, whereas the divisions and accidents (passiones)of being are what is sought after, among them God and the separatedivine beings (Metaph. I.2,Phys. I.3.18). ThomasAquinas’ position is again much influenced by Avicenna: Thesubject of metaphysics is being as being (orens commune),whereas God is that which is aimed at in this science, insofar as heis the cause of all being (In Metaph., prooem.). But, otherthan Avicenna, Thomas argues that God is the proper subject of adifferent science, the principles of which are given in revelation:theology (Summa theol. Ia q.1).

There were three principal positions on the issue in the Latin West(Zimmermann 1998): Albertus and Thomas make God a subject ofmetaphysics only as cause of the subject; a second group, among themRoger Bacon and Giles of Rome, holds that God is one of severalsubjects of metaphysics; a third group argues that God is part of thesubject of metaphysics. The latter position was influentiallyformulated by Henry of Ghent (Pickavé 2007), and taken up bymany other authors, among them Duns Scotus. Scotus develops his ownstandpoint against the authorities of Avicenna, Averroes and Henry ofGhent. He agrees with Avicenna that being as being is the subject andthat the notion of being includes all being, be it material orimmaterial. For Scotus, this notion of being explicitly includes Godwithin the subject of metaphysics (Zimmermann 1998,294–329).

6.2 Primary Concepts

In chapter I.5 of hisMetaphysics, Avicenna argues that justas there are first and self-evident sentences, there are alsofundamental, first known, self-evident concepts, which are common toall beings: “the existent”, “the thing”,“the necessary”. It was due to Avicenna that theprimum cognitum, the first object of knowledge became acentral topic of medieval Latin metaphysics. The question of theprimum cognitum was variously answered. For Guibert ofTournai, Bonaventure and Henry of Ghent, God is theprimumcognitum (Goris 1999), for Thomas Aquinas and Duns Scotus being(ens), for Berthold of Moosburg the good (bonum). Anexample of aprimum cognitum theory influenced by Avicenna isThomas Aquinas’. There cannot be an infinite regress, neither inthe order of demonstration, nor in the order of definition, Thomasargues. This is why there is a first concept: “being”. Itis what is first grasped by the mind, and it is unrestrictedlyuniversal. It is specific for Thomas, however, that the order ofdefinition and of demonstration are not on the same level. Theprinciple of contradiction rests (fundatur) on a conceptualbasis, since it can be reduced to the terms out of which it iscomposed, among which “being” is the first (InMetaph. IV.6; Aertsen 1996, 146–151).

Avicenna’s theory of primary concepts was an important sourcefor the theory of transcendental concepts, which scholasticphilosophers developed in the thirteenth century, taking their cuefrom Aristotle, Avicenna and the Dionysian tradition (Aertsen 2008;Aertsen 2012; Pini 2012). Avicenna bequeathed to the discussion of thetranscendentals not only specific teachings about the notions“being”, “one” and “thing”, butalso the general idea that, ontologically, the primary concepts aremost common since they are true of everything, and that,epistemologically, they are first known since they are self-evidentand not reducable to prior concepts.

6.3 Essence and Existence, Universals and Individuals

Among the most influential philosophical doctrines of Arabic origin isthe distinction between essence (māhiyya,essentia) and existence (wujūd,ens),which the Latin West got to know from Avicenna’sMetaphysics, chapters I.5 and V.1–2. The distinctionwas very influential historically: it found adherents amongphilosophers and theologians of the Arabic, Hebrew and Latincultures. The essence-existence distinction was used by Avicenna inseveral metaphysical contexts, i.e., in the discussion of primaryconcepts, of universals and of the first cause. The followingpresentation focuses on the context of universals. Avicenna’score idea was to differentiate between two components of universals:essence and universality. The essence of “horseness”, touse Avicenna’s example (Metaphysics V.1), is in itselfneither universal nor particular. Only existence, which in itself isdistinct from essence, adds universality or particularity, dependingupon whether “horseness” exists in the mind, that is, as auniversal, or in the exernal world, that is, as a particular. In someof his writings, Avicenna emphasizes that there is universality onlyif the essence is found in several objects in the external world(Marmura 1979, 49).

Thomas Aquinas adopts Avicenna’s distinction already in hisearlyOn Being and Essence (De ente et essentia IV).Essence can be considered either in itself or with respect to itsexistence in the soul or in the particular things. Universality andparticularity are accidents of essence, which in itself is neitheruniversal nor particular. Thomas Aquins adopts the expression“accidents of essence” from Averroes (Comm. magnumMetaph. IV.3). The universal, according to Thomas, is anatura communis, which has existence only in the intellect.Individuals are essences individuated by matter with quantitativedimensions, but only at the time of their origin; later individuationis due to the form. In later writings, Thomas develops his concept ofessence and existence so that existence is that which actualizesessence (Summa theol. Ia q. 3 a. 4) (Wippel 1990; Black1999).

An influential defender of the real distinction between essence andexistence was Giles of Rome. Since he uses the terminology of“thing” (res) for both concepts, he wascriticized for turning “existence” into a thing, whichitself exists only if another thing “existence” is added,and so on ad infinitum. This argument was voiced against the realdistinction by Siger of Brabant and Godfrey of Fontaines (Wippel1982), but it originally comes from Averroes, who flatly rejectsAvicenna’s distinction in hisLong Commentary on theMetaphysics (IV.3).

While some authors take the extreme position that there is only amental distinction between essence and existence, Henry of Ghentdevelops a modified version of Avicenna’s theory. Hedistinguishes between essence in itself and as existing, that is,existing in the mind or in the external world. But he attributes aspecific kind of existence to the essence in itself(Quodlibet I, 9 and III, 9):esse essentiae(“essential being”), which is the essence’s eternalrelation to God as its cause. Theesse existentiae, incontrast, is the essence’s actual existence. Henry thus developsa theory of how essences exist prior to their actual existence in themind or in the world, enlarging on a brief and tentative reference inAvicenna’sMetaphysics I.5 to the “properexistence” (esse proprium) of the essences.

Duns Scotus is also inspired by the Avicennian idea that the commonnature (natura communis), as Scotus calls it, is neithertruly universal nor truly particular in itself and that it isuniversal only as an object of the intellect. But Scotus’account of individuation differs: The common nature is particular onlybecause of a second “reality” in the object, a principleof individuation or contracting difference, which by later authors wascalledhaecceitas (“thisness”). The distinctionbetween the two “realities” nature and thisness is notreal, but formal in the sense that the two are different, but neverexist apart from each other (Ordinatio II, d. 3, p. 1, q.6).

The influence of Arabic metaphysics is much more extensive than thesebrief references to a few well-known thinkers suggest. The influenceof Avicenna and Averroes, especially on the subject of metaphysics andon essence and existence, extends to many authors and over manycenturies, up to sixteenth-century Jesuit authors such as BenedictusPereira, Pedro da Fonseca and Francisco Suárez (Leinsle 1985,ch. 2)

6.4 The First Cause and the Emanation of the Intelligences

The influence of Avicenna’s concept of the first cause as theonly necessary being in itself (wājib al-wujūdbi-ḏātihī,necesse esse per se) and ofhis theory of emanation is apparent already in the twelfth century.Dominicus Gundisalvi, the Avicenna translator, distinguishes in hisProcession of the World (De processione mundi)between the first cause, which is the “necessary being”(necesse esse), and the created beings, which in themselvesare only possible beings. The entire universe proceeds from the firstcause. The principles first created, however, are not theintelligences, as in Avicenna’s metaphysics, but the materialand formal principles of the things (Jolivet 1988, 138–140;Polloni 2017, 532–538).

The anonymous author ofThe Book of First and Second Causes (Liberde causis primis et secundis), which dates from the turn of thethirteenth century, does not adopt the distinction between necessaryand possible beings, but describes the process of emanation instrongly Avicennian terms: From the first cause issues a first createdbeing, an intellect. From this intellect, in turn, emanates a seriesof intelligences, the lowest of which is the active intellect.Emanation happens in triads: From an intelligence emanates, in virtueof its intellectual activity, the form of a celestial sphere, the bodyof a sphere, and another intelligence (ch. 4). The anonymous authoralso draws on theBook of Causes (see the beginning ofsection 6 above), for instance when describing the hierarchy ofintelligences as a decrease in power and unity (ch. 6).

William of Auvergne (d. 1249) is much attracted by Arabic metaphysicaland pyschological theories (which he often indiscriminately attributesto “Aristotle and his followers”) and discusses them atlength, but often rejects them in the end as conflicting withChristian faith. InOn the Universe (De universoII.1), William discusses and rejects the Avicennian emanation system:the necessity of causation through the first cause; the emanation ofthe intelligences from the first intelligence down to the activeintellect; the active intellect as the efficient cause of human souls.He nevertheless tacitly adopts the metaphysical principle “Fromone arises only one” (de uno non nisi unum) fromAvicenna (Teske 1993), in particular within the context of Trinitariantheology (Fischer 2015), and describes the first cause as the“being necessary through itself” (Teske 2002, Fischer2018).

Thomas Aquinas adopts from Avicenna the description of God as thenecessary being, whose essence is its own existence (Summa contragentiles I.22). Avicenna’s influence is also apparent in awell-known passage: the “five ways” (quinqueviae) of proving God’s existence in theSummatheologiae (Ia q. 2 a. 3). The third proof advances via“the possible and the necessary”: It establishes theexistence of something necessary in virtue of itself. The proof ismuch coloured by Avicennian metaphysics, but its direct source isMaimonides’Guide for the Perplexed (II.1), from whichit deviates only in minor respects. A conspicuous element ofMaimonides’ and Thomas’ proof is the premise, notexplicitly formulated by Avicenna, that, in an eternal world, everypossibility is eventually realized, which is a version of theso-called “principle of plenitude” (Davidson 1987,378–388). Thomas, however, rejects the Avicennian theory ofemanation. The creation of the world is not a necessary process, andit does not occur through intermediaries, that is, intelligences orangels. He also rejects Avicenna’s theory of a separate activeintellect as the giver of the forms of the sublunar world and as theontological place of the intelligibles, a theory against which Thomasadvances epistemological arguments in the first place (Summacontra gentiles II.42 and II.76). Albertus Magnus, in contrast,tacitly adopts much of thedator formarum theory in severalof his writings, even though he often voices his criticism of it(Hasse 2012).

The attraction of Avicenna’s position is evident in the work ofSiger of Brabant. In some of his writings, Siger teaches that God asthe first being creates only one being immediately, the firstimmaterial substance, from which emanate the other intelligences, thecelestial spheres and finally the sublunar world, in an eternal andnecessary process. The necessity is not universal, however, but findsits limits in the contingency and in the free will which exists in thesublunar world (De necessitate et contingentia causarum; VanSteenberghen 1991, 346). Duns Scotus, in contrast, is very critical ofAvicenna’s theory of necessary causation through the firstcause. He advances several reasons against it, the most importantbeing that there can only be contingency in the world if the firstcause does not act by necessity (Ordinatio I d. 8 p. 2 q.un).

Several theses on the first cause and the intelligences which areinspired by Avicenna are condemned by the Parisian bishop in 1277,among them: that God is the first necessary cause of the firstintelligence and of the celestial movements (art. 58 and 59), that Goddoes necessarily what is immediately produced by him (art. 53), thatthe active intellect is a substance separate from the human intellect(art. 123), that the rational souls are created by the intelligences(art. 30). Avicenna’s theory of the first cause neverthelesscontinued to influence the scholastic discussion. This is true, forinstance, of the proof for the existence of God, which had been citedby Thomas Aquinas. Peter of Auvergne, Henry of Ghent and Duns Scotustoo draw on Avicenna’s argument from the possible and necessarybeing (Druart 2002; Janssens 2003; Pickavé 2007, ch. 6).

The 1270 and 1277 condemnations were also directed against anothertheory based on Arabic sources: astrological determinism (art. 143,161, 167, 195, 206, 207). The condemnations do not testify to theinfluence of Arabic philosophers proper: Avicenna was critical ofastrology for epistemological reasons and Averroes embeddedastrological doctrines in Peripatetic mainstream theories about theinfluence of the stars. Rather, the condemnations indicate that Arabicastrologers such as Albumasar and Alcabitius were very influential inthe Latin West already in the thireenth century.

7. Ethics

The influence of Arabic ethical and political writings is thin, partlybecause Arabic philosophers were less productive in these fields, andpartly because important works were not translated at all (such asal-Fārābī’sPrinciples of the Citizens of thePerfect State) or as late as in the sixteenth century (such asAverroes’Commentary on Plato’s Republic).Nevertheless, Arabic philosophers, via their teaching on theintellect, exerted an important influence on the border area betweenethics and psychology, and on the discussion of human happiness inparticular.

Al-Fārābī, Avicenna and Averroes share the view thathappiness is reached through the conjunction of the human intellectwith the separate active intellect. They also share an epistemologicaloptimism that for specifically gifted people, which they described asphilosophers or philosopher-prophets, a perfect conjunction ispossible in this life. Albertus Magnus’s theory of happiness ismuch influenced by these Arabic theories. As was mentioned above, headopted from Avicenna and Averroes the concept of an “acquiredintellect” (intellectus adeptus) as the highest levelof conjunction between possible and active intellect. Only in thisstage, a human being truly becomes a human being. Through theconjunction with the active intellect the human intellect contemplatesthe separate substances, and in this consists the “theoreticalhappiness” of man (felicitas contemplativa), ahappiness which is possible in this life (De anima III.3.12)(Müller 2006; on Albertus’ influence see de Libera 2005,329–361). Thomas Aquinas disagrees with the epistemologicalpremisses and the ethical conclusion of this position: Since humanknowledge is bound to the senses, knowledge of the immaterialsubstances is not possible in this life, and neither is perfect humanhappiness (Summa theol. Ia IIae q.3 a.2). But Thomas, whenexplaining beatific vision and human happiness in the afterlife,adopts from Averroes the idea that a separate substance is conjoinedwith the human intellect as its form (Comm. on the SentencesIV, d.49 q.2 a.1; see Taylor 2012)

In 1277, several philosophical theses concerning human happiness andthe good life were condemned: that happiness is to be had in this lifeand not in another (art. 176), that there is no better state (of life)than studying philosophy (art. 40). These articles were apparentlydirected at masters of arts at the university of Paris, among themSiger of Brabant and Boethius of Dacia. As we know from fragments ofSiger’s treatiseOn Happiness (De felicitate),he embraces Averroes’ thesis that all intellects are madeblessed through the conjunction with the active intellect. InSiger’s interpretation, human beings in such a state think Godby an intellection which is God himself. There are many indicationsthat Siger was convinced that the knowledge of the separate substancesand thus the attaining of human happiness is possible in this life(Steel 2001, 227–231). Boethius of Dacia is also convinced thathuman happiness can be reached in this life, which is a happinessproportioned to human capacities, whereas the highest kind ofhappiness as such is reserved to the afterlife (in his treatiseDesummo bono). Boethius appears to be inspired by Arabic theoriesof intellectual ascension, but does not endorse a theory ofconjunction, as does Siger. His conviction that thephilosopher’s life is the only true life echoes the veryself-confident and elitist stance taken by the major Arabicphilosophers.

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