(Gr. γένος) refers first to the principle of generation (Gr. γένεσις), the genus or stock, then to the multitude of things springing from one principle. In logic genus refers first to the universal that is predicable of many things differing in species; like species, it answers the question "What is it?" Whereas species predicates the whole essence, genus predicates the common and determinable part of the essence of its subject. The genus that is contained under no higher genus is called supreme genus or category. Those contained under higher genera are called subaltern genera.
In Aristotelian dialectics genus is one of the four predicates, constituting one kind of dialectical problem (Topica 101b 37–102b 27; 128b 14–139a 20). Genus refers also to the genus subjectum of a science, the limited subject-matter considered by a given science (Anal. post. 76b 11–16).
In things composed of matter and form, matter is remotely the principle of genus inasmuch as it is the principle of all potency. It is also the principle of diverse genera within a category, insofar as in the category of substance matter receives the perfection of act to different degrees. As actuated to one degree, say "sensitive life," it will be the basis of a genus and be in potency either to the further perfection, "rational," or to the imperfection, "non-rational" (St. Thomas Aquinas, In Boeth. Trin., 4.2).
The genus of the logician is, moreover, to be distinguished from the genus of the natural philosopher. The former looks merely for a common ratio, the latter requires in addition a common matter (physical genus).
See Also: predicables; porphyrian tree; definition; matter and form.
The term genus is one of the seven major classification groups that biologists use to identify and categorize living things. These seven groups are hierarchical or range in order of size, and genus is one of the smaller, important, and more frequently used groups. The classification scheme for all living things is: kingdom, phylum, class, order, family, genus, and species.
Coming as it does between the larger group, family, and the smaller group, species, members of the same genus have more in common than those in the same family and less than those in the same species. Although members of the same genus are very similar (like a wolf and a coyote), members of different groups usually cannot breed with one another. Members of the same genus, however, are known to be very closely related in terms of their evolutionary history, and it is obvious that they share the same basic shape and structure as well as similar biochemistry (the chemistry of biological processes) and even behavior.
The group genus is almost always used with the more particular grouping, species. All organisms are referred to scientifically by a two-word, Latin name called a binomial. Humans therefore are Homo sapiens. This example of Homo is unusual, for only one living species occurs in that genus. Most genera are "polyspecific" and contain more than one species. This is especially the case for plants known as sedges (Carex) and insects known as fruit flies (Drosophila), each which has hundreds of species in the genus.
ge·nus / ˈjēnəs/ • n. (pl. gen·e·ra / ˈjenərə/ or ge·nus·es) Biol. a grouping of organisms having common characteristics distinct from those of other such groupings. The genus is a principal taxonomic category that ranks above species and below family, and is denoted by a capitalized Latin name, e.g., Leo. ∎ (in philosophical and general use) a class of things that have common characteristics and that can be divided into subordinate kinds.