Experience enables us to ascribe a more than arbitrary connexion to objects, 35; we are determined to this by custom or habit which is the great guide of human life, 36; but our inference must be based on some fact present to the senses or memory, 37; the customary conjunction between such an object and some other object produces an operation of the soul which is as unavoidable as love, 38; animals also infer one event from another by custom, 82-84; and in man as in animals experimental reasoning depends on a species of instinct or mechanical power that acts in us unknown to ourselves, 85. C. _Belief_, 39-45. Belief differs from fiction or the loose reveries of the fancy by some feeling annexed to it, 39; belief cannot be defined, but may be described as a more lively, forcible, firm, steady conception of an object than can be attained by the imagination alone, 40; it is produced by the principles of association, viz. resemblance, 41; contiguity, 42; causation, 43; by a kind of pre-established harmony between the course of nature and our ideas, 44; this operation of our minds necessary to our subsistence and so entrusted by nature to instinct rather than to reasoning, 45. _Probability_, 46-7. Belief produced by a majority of chances by an inexplicable contrivance of Nature, 46 (cf. 87-8); probability of causes: the failure of a cause ascribed to a secret counteracting cause, 47 (cf. 67); it is universally allowed that chance when strictly examined is a mere negative word, 74. D. _Power_, 49-57. Power, force, energy, necessary connexion must either be defined by analysis or explained by production of the impression from which they are copied, 49; from the first appearance of an object we cannot foretell its effect: we cannot see the power of a single body: we only see sequence, 50. Is the idea of power derived from an internal impression and is it an idea of reflection? 51; it is not derived, as Locke said, from reasoning about power of production in nature, 50 n; nor from consciousness of influence of will over bodily organs, 52; nor from effort to overcome resistance, 52 n (cf. 60 n); nor from influence of will over mind, 53; many philosophers appeal to an invisible intelligent principle, to a volition of the supreme being, and regard causes as only occasions and our mental conceptions as revelations, 54-5; thus diminishing the grandeur of God, 56; this theory too bold and beyond verification by our faculties, and is no explanation, 57; vis inertiae, 57 n.