Sensu is aLatin word meaning "in thesense of". It is used in a number of fields includingbiology,geology,linguistics,semiotics, andlaw. Commonly it refers to how strictly or loosely an expression is used in describing any particular concept, but it also appears in expressions that indicate the convention or context of the usage.
Sensu is theablative case of thenounsensus, here meaning "sense". It is often accompanied by anadjective (in the same case). Three such phrases are:
Søren Kierkegaard uses the phrasesensu eminenti to mean "in the pre-eminent [or most important or significant] sense".[3]
When appropriate,comparative andsuperlative adjectives may also be used to convey the meaning of "more" or "most". Thussensu stricto becomessensu strictiore ("in the stricter sense" or "more strictly speaking") andsensu strictissimo ("in the strictest possible sense" or "most strictly speaking").
| Base phrase | Comparative | Superlative | Meanings |
|---|---|---|---|
| sensu stricto | sensu strictiore | sensu strictissimo | in the strict/stricter/strictest sense |
| sensu lato | sensu latiore | sensu latissimo | in the broad/broader/broadest sense |
| sensu amplo | sensu ampliore | sensu amplissimo | in a relaxed/more relaxed/most relaxed sense |
Current definitions of theplant kingdom (Plantae) offer a biological example of when such phrases might be used. One definition ofPlantae is that it consists of allgreen plants (comprisinggreen algae andland plants), allred algae and allglaucophyte algae; the group defined in this way could be calledPlantae in sensu lato (or simplyPlantae sensu lato). A stricter definition excludes the red and glaucophyte algae; the group defined in this way could be calledPlantae in sensu stricto. An even stricter definition excludes green algae, leaving only land plants; the group defined in this way could be calledPlantae in sensu strictiore, orPlantae in sensu strictissimo.[4]
Conversely, where convenient, some authors derive expressions such as "sensu non strictissimo", meaning "not in the narrowest possible sense".[5]
A similar form is in use to indicate the sense of a particular context, such as "Nonmonophyletic groups are ... nonnatural (sensu cladistics) in that ..."[6] or "... computation of a cladogram (sensu phenetics) ..."[7]
Also the expressionsensuauctorum (abbreviation:sensu auct.) is used to mean "in the sense of certain authors", who can be designated or described. It normally refers to a sense which is considered invalid and may be used in place of the author designation of a taxon in such a case (for instance,"Tricholoma amethystinum sensu auct." is an erroneous name for a mushroom which should really be "Lepista personata (Fr.) Cooke").[8]
A related usage is in a concept-author citation ("sec. Smith", or "sensu Smith"), indicating that the intended meaning is the one defined by that author.[7][9] (Here "sec." is an abbreviation of "secundum", meaning "following" or "in accordance with".) Such an author citation is different from the citation of the nomenclatural"author citation" or "authority citation". In biological taxonomy the author citation following the name of a taxon simply identifies the author who originally published the name and applied it to thetype, the specimen or specimens that one refers to in case of doubt about the definition of a species. Given that an author (such as Linnaeus, for example) was the first to supply a definitetype specimen and to describe it, it is to be hoped that his description would stand the tests of time and criticism, but even if it does not, then as far as practical the name that he had assigned will apply. It still will apply in preference to any subsequent names or descriptions that anyone proposes, whether his description was correct or not, and whether he had correctly identified itsbiological affinities or not. This does not always happen of course; all sorts of errors occur in practice. For example, a collector might scoop a netful of small fish and describe them as a new species; it then might turn out that he had failed to notice that there were several (possibly unrelated) species in the net. It then is not clear what he had named, so his name can hardly be taken seriously, eithers.s. or s.l.[citation needed]
After a species has been established in this manner, specialisttaxonomists may work on the subject and make certain types of changes in the light of new information. In modern practice it is greatly preferred that the collector of the specimens immediately passes them to specialists for naming; it is rarely possible for non-specialists to tell whether their specimens are of new species or not, and in modern times not many publications or their referees would accept an amateur description.[citation needed]
In any event, the person who finally classifies and describes a species has the task oftaxonomic circumscription.Circumscription means in essence that anyone competent in the matter can tellwhich creatures are included in the species described, and which are excluded. It is in this process ofspecies description that the question of thesense arises, because that is where the worker produces and argues their view of the proper circumscription. Equally, or perhaps even more strongly, the arguments for deciding questions concerninghigher taxa such asfamilies ororders, require very difficult circumscription, where changing thesense applied could totally upset an entire scheme of classification, either constructively or disastrously.[citation needed]
Note that the principles of circumscription apply in various ways in non-biological senses. In biological taxonomy the usual assumption is that circumscription reflects the shared ancestry perceived as most likely in the light of the currently available information; in geology or legal contexts far wider and more arbitrary ranges of logical circumscription commonly apply, not necessarily formally uniformly. However, the usage of expressions incorporatingsensu remains functionally similarly intelligible among the fields. In geology for example, in which the concept of ancestry is looser and less pervasive than in biology, one finds usages such as:
Sensu is used in thetaxonomy of living creatures to specify whichcircumscription of a giventaxon is meant, where more than one circumscription can be defined.
"The familyMalvaceaes.s. is cladisticallymonophyletic."
This means that the members of the entire family of plants under the name Malvaceae (strictly speaking), over 1000 species, including the closest relatives ofcotton andhibiscus, all descend from a shared ancestor, specifically, that they, and no other extant planttaxa, share a notionalmost recent common ancestor (MRCA).[12] If this is correct, that ancestor might have been a single species of plant. Conversely the assertion also means that the family includes all surviving species descended from that ancestor. Other species of plants that some people might (broadly speaking ors.l.) have included in the family would not have shared that MRCA (oripso facto they too would have been members of the family Malvaceae s.s. In short, this circumscriptions.s. includes all and only plants that have descended from that particular ancestral stock.
"In the broaderAPG circumscription the family Malvaceaes.l. includes Malvaceaes.s. and also the familiesBombacaceae,Sterculiaceae andTiliaceae."
Here the circumscription is broader, stripped of some of its constraints by sayingsensu lato; that is what speaking morebroadly amounts to. Discarding such constraints might be for historical reasons, for example when people usually speak of thepolyphyletic taxon because the members were long believed to form a "true" taxon and the standard literature still refers to them together. Alternatively a taxon might include members simply because they form a group that is convenient to work with in practice.
In this example, we can know from additional sources that we are dealing with the latter case: by adding other groups of plants to the family Malvaceaes.l., including those related tocacao,cola,durian, andjute, the APG circumscription omits some of the criteria by which the new members previously had been excluded. Thes.l. group remains monophyletic.[12][13]
"The 'clearly non-monophyletic' seriesCyrtostylissensu A.S. George has been virtually dismantled..."[14]
This remark specifiesAlex George's particular description of that series. It is a different kind of circumscription, alluding to the fact that A.S. George called them a series. "Sensu A.S. George" means that A.S. George discussed theCyrtostylis in that series, and that members of that series are the ones under discussion in the same sense—how A. S. George saw them; the current author might or might notapprove George's circumscription, but George's is the circumscription currently under consideration.
