Nor can this objection be neutralized by saying, it is a mere matter of opinion--a mere prejudice originating in rivalry.

For, though we have ample choice of terms, and may frequently assign to particular words a meaning and an explanation which are in some degree arbitrary; yet whenever we attempt to define things under the name which custom has positively fixed upon them, we are no longer left to arbitrary explications; but are bound to think and to say that only which shall commend itself to the understanding of others, as being altogether true to nature.

When a word is well understood to denote a particular object or class of objects, the definition of it ought to be in strict conformity to what is known of the real being and properties of the thing or things contemplated.

A definition of this kind is a proposition susceptible of proof and illustration; and therefore whatsoever is erroneously assumed to be the proper meaning of such a term, may be refuted.

But those persons who take every thing upon trust, and choose both to learn and to teach mechanically, often become so slavishly habituated to the peculiar phraseology of their text-books, that, be the absurdity of a particular expression what it may, they can neither discover nor suspect any inaccuracy in it.