and nominal Essences.

Secondly, The names of simple ideas and modes signify always the real
as well as nominal essence of their species. But the names of natural
substances signify rarely, if ever, anything but barely the nominal
essences of those species; as we shall show in the chapter that treats
of the names of substances in particular.


4. Thirdly, Names of simple Ideas are undefinable.

Thirdly, The names of simple ideas are not capable of any definition;
the names of all complex ideas are. It has not, that I know, been yet
observed by anybody what words are, and what are not, capable of being
defined; the want whereof is (as I am apt to think) not seldom the
occasion of great wrangling and obscurity in men's discourses, whilst
some demand definitions of terms that cannot be defined; and others
think they ought not to rest satisfied in an explication made by a more
general word, and its restriction, (or to speak in terms of art, by a
genus and difference,) when, even after such definition, made according
to rule, those who hear it have often no more a clear conception of the
meaning of the word than they had before. This at least I think, that
the showing what words are, and what are not, capable of definitions,
and wherein consists a good definition, is not wholly besides our
present purpose; and perhaps will afford so much light to the nature
of these signs and our ideas, as to deserve a more particular
consideration.


5. If all names were definable, it would be a Process IN INFINITUM.