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Why the Genus is ordinarily made use of in Definitions.       §10. This may shew 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
— 413 —
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 Sub-
stance, 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 it self
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 shew 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
Logick, 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.
Locke Hum III, 3, §10, pp. 412-413