| It is certain, that this idea arises only from a relation to a present impression. |
| It is certain, that the belief super-adds nothing to the idea, but only changes our manner of conceiving it, and renders it more strong and lively. |
| The present conclusion concerning the influence of relation is the immediate consequence of all these steps; and every step appears to me sure end infallible. |
| There enters nothing into this operation of the mind but a present impression, a lively idea, and a relation or association in the fancy betwixt the impression and idea; so that there can be no suspicion of mistake. |
| In order to put this whole affair in a fuller light, let us consider it as a question in natural philosophy, which we must determine by experience and observation. |
| I suppose there is an object presented, from which I draw a certain conclusion, and form to myself ideas, which I am said to believe or assent to. |
| Here it is evident, that however that object, which is present to my senses, and that other, whose existence I infer by reasoning, may be thought to influence each other by their particular powers or qualities; yet as the phenomenon of belief, which we at present examine, is merely internal, these powers and qualities, being entirely unknown, can have no hand in producing it. |
| It is the present impression, which is to be considered as the true and real cause of the idea, and of the belief which attends it. |
| We must therefore endeavour to discover by experiments the particular qualities, by which it is enabled to produce so extraordinary an effect. |
| First then I observe, that the present impression has not this effect by its own proper power and efficacy, and when considered alone, as a single perception, limited to the present moment. |
| I find, that an impression, from which, on its first appearance, I can draw no conclusion, may afterwards become the foundation of belief, when I have had experience of its usual consequences. |
| We must in every case have observed the same impression in past instances, and have found it to be constantly conjoined with some other impression. |
| This is confirmed by such a multitude of experiments, that it admits not of the smallest doubt. |
| From a second observation I conclude, that the belief, which attends the present impression, and is produced by a number of past impressions and conjunctions; that this belief, I say, arises immediately, without any new operation of the reason or imagination. |
| Of this I can be certain, because I never am conscious of any such operation, and find nothing in the subject, on which it can be founded. |
| Now as we call every thing CUSTOM, which proceeds from a past repetition, without any new reasoning or conclusion, we-may establish it as a certain truth, that all the belief, which follows upon any present impression, is derived solely from that origin. |
| When we are accustomed to see two impressions conjoined together, the appearance or idea of the one immediately carries us to the idea of the other. |
| Being fully satisfyed on this head, I make a third set of experiments, in order to know, whether any thing be requisite, beside the customary transition, towards the production of this phaenomenon of belief. |
| I therefore change the first impression into an idea; and observe, that though the customary transition to the correlative idea still remains, yet there is in reality no belief nor perswasion. |
| A present impression, then, is absolutely requisite to this whole operation; and when after this I compare an impression with an idea, and find that their only difference consists in their different degrees of force and vivacity, I conclude upon the whole, that belief is a more vivid and intense conception of an idea, proceeding from its relation to a present impression. |
| Thus all probable reasoning is nothing but a species of sensation. |