But when we would guard against the possibility of misapprehension, and show precisely what is meant by a word, we must fairly define it.

There are, however, in every language, many words which do not admit of a formal definition.

The import of all definitive and connecting particles must be learned from usage, translation, or derivation; and nature reserves to herself the power of explaining the objects of our simple original perceptions.

"All words standing for complex ideas are definable; but those by which we denote simple ideas, are not.
For the perceptions of this latter class, having no other entrance into the mind, than by sensation or reflection, can be acquired only by experience."-- _Duncan's Logic_, p.63.

"And thus we see, that as our simple ideas are the materials and foundation of knowledge, so the names of simple ideas may be considered as the elementary parts of language, beyond which we cannot trace the meaning and signification of words.