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648, which in some cases produces belief; which is only the vivacity of a perception, 85, 86; it is only by experience that we can pass from the impression to the idea: when we consider the constant conjunction of two objects in a regular order of succession and contiguity, 'without further ceremony' we call the one cause and the other effect, and infer the existence of the one from that of the other, 87 (cf. 102, 149, 153); but constant conjunction can never give rise to any new idea such as necessary connexion, it only gives rise to an inference: does this inference give rise to necessary connexion? 88 (cf. 155, 163).

B. [Uniformity of Nature.] This inference or transition from impression to idea does not arise from experience through reason, for that would require the principle of the uniformity of nature, viz. that the future will resemble the past, which is provable neither demonstratively, 89, nor probably, for probable reasoning itself assumes the principle, 89 (cf. 104, 105, 134); nor can we justify the inference by arguments from production, power, or efficacy: such arguments either circular or have no end 90 (cf. 632). Thus even when experience has informed us of the constant conjunction of two objects' 'tis impossible for us to satisfy ourselves by our reason why we should extend that experience beyond those particular instances which have fallen under our observation,' 91 (v. § 7. B).

C. The inference then depends solely on the union of the ideas in the fancy by three general principles—resemblance (97, cf. 168); contiguity (100, cf. 168); and causation, 92 (cf. 101, 109), which = 'habitual union in the imagination,' 93; thus causation as a natural relation is the basis of causation as a philosophical relation, 94, cf. 11, 15, 101, 170 (v. § 7. C.).

§ 7. A. [Belief.] The conclusion of all reasoning from cause and effect is a belief (q. v.) in the existence of an object, which is the same as the idea of the object, only conceived in a different manner. 96 (cf. 34, 37, 153, 623); this manner='with additional force or vivacity:' a belief='a lively idea related to or associated with a present impression' by means of custom, 97 (cf. 102), the impression communicating to its related idea a share of its own force or vivacity, 98; there is nothing in the whole operation but 'a present impression, a lively idea, and a relation or association in the fancy between the impression and the idea,' 101; experimental proof of this, 102: thus 'all probable reasoning is nothing but a species of sensation,' thus (cf. 132, 141, 149, 173 f.), 405-6, 458.

B. Inference from past experience does not imply reflection on it, still less 'the formation of any principle concerning it,' such as that of the uniformity of nature, 104 (v.§ 6. B.); but in some cases reflection on past experience 'produces the belief without the custom,' or rather 'produces the custom in an oblique and artificial manner,