CHAPTER VI.
LANGUAGE--PROPOSITIONS CONCERNING NECESSARY TRUTHS.
Though we may accept Hume's conclusion that speechless animals think, believe, and reason; yet, it must be borne in mind, that there is an important difference between the signification of the terms when applied to them and when applied to those animals which possess language.

The thoughts of the former are trains of mere feelings; those of the latter are, in addition, trains of the ideas of the signs which represent feelings, and which are called "words." A word, in fact, is a spoken or written sign, the idea of which is, by repetition, so closely associated with the idea of the simple or complex feeling which it represents, that the association becomes indissoluble.
No Englishman, for example, can think of the word "dog" without immediately having the idea of the group of impressions to which that name is given; and conversely, the group of impressions immediately calls up the idea of the word "dog." The association of words with impressions and ideas is the process of naming; and language approaches perfection, in proportion as the shades of difference between various ideas and impressions are represented by differences in their names.
The names of simple impressions and ideas, or of groups of co-existent or successive complex impressions and ideas, considered _per se_, are substantives; as redness, dog, silver, mouth; while the names of impressions or ideas considered as parts or attributes of a complex whole, are adjectives.

Thus redness, considered as part of the complex idea of a rose, becomes the adjective red; flesh-eater, as part of the idea of a dog, is represented by carnivorous; whiteness, as part of the idea of silver, is white; and so on.
The linguistic machinery for the expression of belief is called _predication_; and, as all beliefs express ideas of relation, we may say that the sign of predication is the verbal symbol of a feeling of relation.

The words which serve to indicate predication are verbs.

If I say "silver" and then "white," I merely utter two names; but if I interpose between them the verb "is," I express a belief in the co-existence of the feeling of whiteness with the other feelings which constitute the totality of the complex idea of silver; in other words, I predicate "whiteness" of silver.
In such a case as this, the verb expresses predication and nothing else, and is called a copula.