T 1.3.8.15

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|pression, I am able to conclude from this idea, that such an impression did once exist; and as this conclusion is attended with belief, it may be ask'd, from whence are the qualities of force and vivacity deriv'd, which constitute this belief? And to this I answer very readily, from the present idea. For as this idea is not here consider'd, as the representation of any absent object, but as a real perception in the mind, of which we are intimately conscious, it must be able to bestow on whatever is related to it the same quality, call it firmness, or solidity, or force, or vivacity, with which the mind reflects upon it, and is assur'd of its present existence. The idea here supplies the place of an impression, and is entirely the same, so far as regards our present purpose.