10. Why the genus is ordinarily made use of in definitions.
This may show us the reason why, in the defining of
words, which is nothing but declaring their signification, we make use of the genus, or next general word that
comprehends it. Which is not out of necessity, but only to save the labour of enumerating the several simple ideas
which the next general word or genus stands for; or, perhaps, sometimes the shame of not being able to do it. But
though defining by genus and differentia (I crave leave to use these terms of art, though originally Latin, since
they most properly suit those notions they are applied to), I say, though defining by the genus be the shortest way,
yet I think it may be doubted whether it be the best. This I am sure, it is not the only, and so not absolutely
necessary. For, definition being nothing but making another understand by words what idea the term defined
stands for, a definition is best made by enumerating those simple ideas that are combined in the signification of
the term defined: and if, instead of such an enumeration, men have accustomed themselves to use the next general
term, it has not been out of necessity, or for greater clearness, but for quickness and dispatch sake. For I think that,
to one who desired to know what idea the word man stood for; if it should be said, that man was a solid extended
substance, having life, sense, spontaneous motion, and the faculty of reasoning, I doubt not but the meaning of the
term man would be as well understood, and the idea it stands for be at least as clearly made known, as when it is
defined to be a rational animal: which, by the several definitions of animal, vivens, and corpus, resolves itself into
those enumerated ideas. I have, in explaining the term man, followed here the ordinary definition of the schools;
which, though perhaps not the most exact, yet serves well enough to my present purpose. And one may, in this
instance, see what gave occasion to the rule, that a definition must consist of genus and differentia; and it suffices
to show us the little necessity there is of such a rule, or advantage in the strict observing of it. For, definitions, as
has been said, being only the explaining of one word by several others, so that the meaning or idea it stands for
may be certainly known; languages are not always so made according to the rules of logic, that every term can
have its signification exactly and clearly expressed by two others. Experience sufficiently satisfies us to the
contrary; or else those who have made this rule have done ill, that they have given us so few definitions
conformable to it. But of definitions more in the next chapter.
