Manifold and admirable are the purposes to which the external signs of passion are made subservient by the author of our nature. What are occasionally mentioned above, make but a part. Several final causes remain to be unfolded; and to this task I apply myself with alacrity. In the first place, the signs of internal agitation that are displayed externally to every spectator, tend to fix the signification of many terms. The only effectual means to ascertain the meaning of any doubtful word, is an appeal to the thing it represents. Hence the ambiguity of words expressive of things that are not objects of external sense; for in that case an appeal is denied. Passion, strictly speaking, is not an object of external sense: but its external signs are; and by means of these signs, passions may be appealed to, with tolerable accuracy. Thus the words that denote our passions, next to those that denote external objects, have the most distinct meaning. Words signifying internal action and the more delicate feelings, are less distinct. This defect with respect to internal action, is what chiefly occasions the intricacy of logic. The terms of that science are far from being sufficiently ascertained, even after the care and labour bestowed by an eminent writer[43]: to whom however the world is greatly indebted, for removing a mountain of rubbish, and moulding the subject into a rational and correct form. The same defect is remarkable in criticism, which has for its object the more delicate feelings. The terms that denote these feelings, are not more distinct than those of logic. To reduce this science of criticism to any regular form, has never once been attempted. However rich the ore may be, no critical chymist has been found to give us a regular analysis of its constituent parts, and to distinguish each by its own name. In the second place, society among individuals is greatly promoted by this universal language. The distance and reserve that strangers naturally discover, show its utility. Looks and gestures give direct access to the heart; and lead us to select with tolerable accuracy the persons who may be trusted. It is surprising how quickly, and for the most part how correctly, we judge of character from external appearances.