positions, and the influence which they have over our affections and actions, make part of the ideas that adhere to words by association; which part, however, could not properly be considered in this section.
Cor. I. It follows from this proposition, that words may be distinguished into the four classes mentioned under the twelfth proposition.
1. Such as have ideas only.
2. Such as have both ideas and definitions.
3. Such as have definitions only.
4. Such as have neither ideas nor definitions.
Under definition I here include description, or any other way of explaining a word by other words, excepting that by a mere synonymous term; and I exclude from the number of ideas the visible idea of the character of a word, and the audible one of its sound; it being evident, that every word heard may thus excite a visible idea, and every word seen an audible one. I exclude also all ideas that are either extremely faint, or extremely variable.
It is difficult to fix precise limits to these four classes, so as to determine accurately where each ends, and the next begins; and, if we consider these things in the most general way, there is perhaps no word which has not both an idea and a definition, i.e. which is not attended by some one or more internal feelings occasionally, and which may not be explained, in some imperfect manner at least, by other words. I will give some instances of words which have the fairest right to each class.
The names of simple sensible qualities are of the first class. Thus white, sweet, &c. excite ideas; but cannot be defined. It is to be observed here, that this class of words stands only for the stable part of the ideas respectively, not for the several variable particularities, circumstances, and adjuncts, which intermix themselves here.
The names of natural bodies, animal, vegetable, mineral, are of the second class; for they excite aggregates of sensible ideas, and at the same time may be defined (as appears from the writings of natural historians) by an enumeration of their properties and characteristics. Thus likewise geometrical figures have both ideas and definitions. The definitions in both cases are so contrived as to leave out all the variable particularities of the ideas, and to be also more full and precise, than the ideas generally are in the parts that are of the permanent nature.
Algebraic quantities, such as roots, powers, surds, &c. belong to the third class, and have definitions only. The same may be said of scientifical terms of art, and of most abstract general terms, moral, metaphysical, vulgar: however, mental emotions are apt to attend some of these even in passing slightly over the ear; and these emotions may be considered as ideas belonging to the terms respectively. Thus the very words, gratitude, mercy,
