Our Abstract Ideas are to us the Measures of the Species we make in instance in that of Man.
There are creatures in the world that have shapes like ours, but are hairy, and want language and reason.

There are naturals amongst us that have perfectly our shape, but want reason, and some of them language too.

There are creatures, as it is said, (sit fides penes authorem, but there appears no contradiction that there should be such,) that, with language and reason and a shape in other things agreeing with ours, have hairy tails; others where the males have no beards, and others where the females have.

If it be asked whether these be all men or no, all of human species?
it is plain, the question refers only to the nominal essence: for those of them to whom the definition of the word man, or the complex idea signified by that name, agrees, are men, and the other not.

But if the inquiry be made concerning the supposed real essence; and whether the internal constitution and frame of these several creatures be specifically different, it is wholly impossible for us to answer, no part of that going into our specific idea: only we have reason to think, that where the faculties or outward frame so much differs, the internal constitution is not exactly the same.