Now as after one experiment of this kind, the mind, upon the appearance either of the cause or the effect, can draw an inference concerning the existence of its correlative; and as a habit can never be acquir'd merely by one instance; it may be thought, that belief cannot in this case be esteem'd the effect of custom. But this difficulty will vanish, if we consider, that tho' we are here suppos'd to have had only one experiment of a particular effect, yet we have many millions to convince us of this principle; that like objects, plac'd in like circumstances, will always produce like effects; and as this principle has establish'd itself by a sufficient custom, it bestows an evidence and firmness on any opinion, to which it can be apply'd. The connexion of the ideas is not habitual after one experiment; but this connexion is comprehended under another principle, that is habitual; which brings us back to our hypothesis. In all cases we transfer our experience to instances, of which we have no experience, either expressly or tacitly, either directly or indirectly.
I must not conclude this subject without observing, that 'tis very difficult to talk of the operations of the mind with perfect propriety and exactness; because common language has seldom made any very nice distinctions among them, but has generally call'd by the same term all such as nearly resemble each other. And as this is a source almost inevitable of obscurity and confusion in the author; so it may frequently give rise to doubts and objections in the reader, which otherwise he wou'd never have dream'd of. Thus my general position, that an opinion or belief is nothing but a strong and lively idea deriv'd from a present impression related to it, may be liable to the following objection, by reason of a little ambiguity in those words strong and lively. It may be said, that not only an impression may give rise to reasoning, but that an idea may also have the same influence; especially upon my principle, that all our ideas are deriv'd from correspondent impressions. For suppose I form at present
an idea, of which I have forgot the correspondent im-