Diairesis (Ancient Greek:διαίρεσις,romanized: diaíresis, "division") is a form ofclassification used inancient (especiallyPlatonic)logic that serves to systematize concepts and come to definitions. When defining a concept using diairesis, one starts with a broad concept, then divides this into two or more specific sub-concepts, and this procedure is repeated until a definition of the desired concept is reached.Aristotle makes extensive use of diaresis in categorization as basis forsyllogizing. He makes clear, however, that definition by diaresis does not in itself prove anything.[1] Apart from this definition, the procedure also results in ataxonomy of other concepts, ordered according to a general–specific relation.
The founder of diairesis as a method wasPlato. Later ancient logicians (including Aristotle) and practitioners of other ancient sciences have employed diairetic modes of classification, e.g., to classify plants in ancientbiology.
Diairesis is Plato's later method ofdefinition based on division, developed in thePlatonic dialoguesPhaedrus,Sophist,Statesman, andPhilebus. Further applications are found in theLaws[2] andTimaeus. It is a means of attempting to reach a definition by which a collection of candidates is repeatedly divided into two parts with one part eliminated until a suitable definition is discovered.
A complementary term ismerismos (cf. Englishmerism: parsing or the distinguishing of parts, as opposed todiairesis, which is the division of a genus into its parts).
For example, in theSophist (§235B), the Eleatic Stranger is examining illusions, which consist of words and "visual objects." By usingdiairesis, he divides visual objects, by which it becomes clear he means works of art, into two categories:eikastikētechnē, the art of making likenesses oreikones; andphantastikē technē, the art of creating illusionary appearances. The Stranger is much more fond of the former; the latter is only created to produce an appearance of beauty.
Opinions about possible forerunners of Platonicdiairesis are varying; they even reach back untilHomer. Also an adoption from the fields of mathematics has been considered,[3] like one from musicology,[4] one from pre-scientific and everyday divisions[5] and one from medicine.[6] About forerunners in the field of philosophy there are as well different opinions. Under consideration areProdicus of Ceos,[7][8]Democritus,Leucippus,[9] and thesophists.[10] It was even suggested that Plato says that he himself found the new method,[11] which shows that it is possible that Plato had no forerunners at all.[12]
The platonic method of division is found to be applied at the first steps of classifying biology, namely in the zoology ofAristotle[13] and in the botany ofTheophrastus.[14] Diairesis is central toGalen's therapeutics; see for example 'Therapeutics to Glaucon' 1 (XI, 4 K), where Galen, attributing the method to Plato, asserts that 'the errors of the [medical] sects and whatever mistakes the majority of physicians make in the care of the sick have incompetent division as their principal and major cause' (tr. Dickson.)[15] Philosophically relevant methodical divisions or statements about the method ofdiairesis can be found in members of the Platonic Academy (especiallySpeusippus[16] andXenocrates), of thePeripatetic school (especiallyAristotle,Aristoxenus,Theophrastus), ofStoicism (especiallyChrysippus), ofMiddle Platonism (especiallyAlcinous,Maximus of Tyre,Philo) and ofNeoplatonism (especiallyPlotinus,Porphyry). In medieval times the so-called method ofdivisio was a common method.[17]