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707 kinds of (1) the discovery of proportions of ideas considered as such, (2) the conformity of our ideas of objects to their real existence, 448; truth or falsehood consists in an agreement or disagreement either to the real relations of ideas, or to real existence and matter of fact. Thus since passions, volitions, and actions are 'original facts and realities complete in themselves,' they cannot be either true or false, 458 cf. 415; only judgments can be true or false, 416, 458; an action improperly called true as joined with a true judgment, 459; love of, and curiosity, 428 f.; why truth pleases; (1) because it requires exertion and attention, (2) because it is useful, though utility only acts here through sympathy and by fixing our attention, 449-51.

Understanding—acts of, 97; subsequent to conception and conditioned by it, 164; contiguity, succession, and resemblance independent of and antecedent to the operations of the understanding, 168; never observes any real connexion among objects, 260; founded on imagination or the vivacity of our ideas, 265; we cannot adhere solely to the understanding, that is, to the general and more established properties of the imagination,' for 'understanding, when it acts alone according to its most general principles entirely subverts itself,' 267 (cf. 182 f.); opposed to imagination. 371 n; remedies the incommodiousness of the affections, 489, by changing their direction, 492; understanding, as well as the affections, necessary to all the actions of human nature; the philosophers who invented the 'state of nature' considered the effects of the latter without those of the former, 493: corrects appearances of the senses, 632.

Uniformity of nature—indemonstrable, 89; the foundation not the result of probability, 90; the principle oil based on custom, 105, 133, 134; the basis of inference after one experiment, 105; a source of probability indirectly, 135 (v. Cause, § 6. B).

Unity—distinguished from identity, 200.

Usual—=natural (q.v.), 483, 549; the usual force of the passions a standard of praise, 483, 488.

Utility—makes truth agreeable, but only by sympathy, 450; a source of beauty, 576; a source of our sentiments of morals through sympathy, 577.

Vacuum—idea of, 53 f., 638 (v. Space).

Vanity—a 'social passion,' 491.

Violent—impressions of reflection divided into calm and violent, the passions being violent, 276; violent to be distinguished from strong passions, and calm from weak, 419.

Vivacity—alone distinguishes impressions from ideas, 1 (cf. 319); vagueness of the term 105 cf. 629; communicated by an impression to