§ 3. Of these five names, two, Genus and Species, are not only used by naturalists in a technical acceptation not precisely agreeing with their philosophical meaning, but have also acquired a popular acceptation, much more general than either. In this popular sense any two classes, one of which includes the whole of the other and more, may be called a Genus and a Species. Such, for instance, are Animal and Man; Man and Mathematician. Animal is a genus; Man and Brute are its two species; or we may divide it into a greater number of species, as man, horse, dog, &c. _Biped_, or _two-footed animal_, may also be considered a genus, of which man and bird are two species. _Taste_ is a genus, of which sweet taste, sour taste, salt taste, &c. are species. _Virtue_ is a genus; justice, prudence, courage, fortitude, generosity, &c. are its species.
The same class which is a genus with reference to the sub-classes or species included in it, may be itself a species with reference to a more comprehensive, or, as it is often called, a superior, genus. Man is a species with reference to animal, but a genus with reference to the species mathematician. Animal is a genus, divided into two species, man and brute; but animal is also a species, which, with another species, vegetable, makes up the genus, organized being. Biped is a genus with reference to man and bird, but a species with respect to the superior genus, animal. Taste is a genus divided into species, but also a species of the genus sensation. Virtue, a genus with reference to justice, temperance, &c., is one of the species of the genus, mental quality.
In this popular sense the words Genus and Species have passed into common discourse. And it should be observed that, in ordinary parlance, not the name of the class, but the class itself, is said to be the genus or species; not, of course, the class in the sense of each individual of that class, but the individuals collectively, considered as an aggregate whole; the name by which the class is designated being then called not the genus or species, but the generic or specific name. And this is an admissible form of expression; nor is it of any importance which of the two modes of speaking we adopt, provided the rest of our language is consistent with it; but if we call the class itself the genus, we must not talk of predicating the genus. We predicate of man the _name_ mortal; and by predicating the name, we may be said, in an intelligible sense, to predicate what the name expresses, the _attribute_ mortality; but in no allowable sense of the word predication do we predicate of man the _class_ mortal. We predicate of him the fact of _belonging_ to the class.