Of knowledge

PART the resemblances and differences betwixt a poetical enthusiasm and a serious conviction. In the mean time, I cannot forbear observing, that the great difand ference in their feeling proceeds, in some measure, probability. from reflection and general rules. We observe, that the vigour of conception which fictions receive from poetry and eloquence, is a circumstance merely accidental, of which every idea is equally susceptible; and that such fictions are connected with nothing that is real, This observation makes us only lend ourselves, so to speak, to the fiction, but causes the idea to feel very different from the eternal established persuasions founded on memory and custom. They are somewhat of the same kind; but the one is much inferior to the other, both in its causes and effects,

A like reflection on general rules keeps us from augmenting our belief upon every increase of the force and vivacity of our ideas. Where an opinion admits of no doubt, or opposite probability, we attribute to it a full conviction; though the want of resemblance, or contiguity, may render its force inferior to that of other opinions. 'Tis thus the understanding corrects the appearances of the senses, and makes us imagine, that an object at twenty foot distance seems even to the eye as large as one of the same dimensions at

ten,

We may observe the same effect of poetry in a lesser degree; only with this difference, that the least reflection dissipates the illusions of poetry, and places the objects in their proper light. 'Tis however certain, that in the warmth of a poetical enthusiasm, a poet has a counterfeit belief, and even a kind of vision of his objects; and if there be any shadow of argument to support this belief, nothing contributes more

to his full conviction than a blaze of poetical figures SECT. and images, which have their effect upon the poet himself, as well as upon his readers.

X.

Of the influence

SECTION XI.

OF THE PROBABILITY OF CHANCES.

BUT in order to bestow on this system its full force and evidence, we must carry our eye from it a moment to consider its consequences, and explain, from the same principles, some other species of reasoning which are derived from the same origin.

Those philosophers who have divided human reason into knowledge and probability, and have defined the first to be that evidence which arises from the com parison of ideas, are obliged to comprehend all our ar guments from causes or effects under the general term of probability. But though every one be free to use his terms in what sense he pleases; and accordingly, in the precedent part of this discourse, I have followed this method of expression; 'tis however certain, that in common discourse we readily affirm, that many arguments from causation exceed probability, and may be received as a superior kind of evidence. One would appear ridiculous who would say, that 'tis only probable the sun will rise to-morrow, or that all men must die; though 'tis plain we have no further assurance of these facts than what experience affords us. For this reason t'would perhaps be more convenient, in order at once to preserve the common signification of words,

of belief.

III.

PART and mark the several degrees of evidence, to distinguish human reason into three kinds, viz. that from knowledge, from proofs, and from probabilities. By and knowledge, I mean the assurance arising from the probability. comparison of ideas. By proofs, those arguments

Of

knowledge

0009✓

which are derived from the relation of cause and effect, and which are entirely free from doubt and uncertainty. By probability, that evidence which is still attended with uncertainty. 'Tis this last species of reasoning I proceed to examine.

SUMMARY

Probability or reasoning from conjecture may be divided into two kinds, viz. that which is founded on chance, and that which arises from causes. We shall consider each of these in order.

The idea of cause and effect is derived from experience, which, presenting us with certain objects constantly conjoined with each other, produces such a habit of surveying them in that relation, that we cannot, without a sensible violence, survey them in any other. On the other hand, as chance is nothing real in itself, and, properly speaking, is merely the negation of a cause, its influence on the mind is contrary to that of causation; and 'tis essential to it to leave the imagination perfectly indifferent, either to consider the existence or non-existence of that object which is regarded as contingent. A cause traces the way to our thought, and in a manner forces us to survey such certain objects in such certain relations. Chance can only destroy this determination of the thought, and leave the mind in its native situation of indifference; in which, upon the absence of a cause, 'tis instantly reinstated.

Since, therefore, an entire indifference is essential to chance, no one chance can possibly be superior to another, otherwise than as it is composed of a superior

number of equal chances. For if we affirm that one chance can, after any other manner, be superior to another, we must at the same time affirm, that there is something which gives it the superiority, and determines the event rather to that side than the other: that is, in other words, we must allow of a cause, and destroy the supposition of chance, which we had before established. A perfect and total indifference is essential to chance, and one total indifference can never in itself be either superior or inferior to another. This truth is not peculiar to my system, but is acknowledged by every one that forms calculations concerning chances.

And here 'tis remarkable, that though chance and causation be directly contrary, yet 'tis impossible for us to conceive this combination of chances, which is requisite to render one hazard superior to another, without supposing a mixture of causes among the chances, and a conjunction of necessity in some particulars, with a total indifference in others. Where nothing limits the chances, every notion that the most extravagant fancy can form is upon a footing of equality; nor can there be any circumstance to give one the advantage above another. Thus, unless we allow that there are some causes to make the dice fall, and preserve their form in their fall, and lie upon some one of their sides, we can form no calculation concerning the laws of hazard. But supposing these causes to operate, and supposing likewise all the rest to be indifferent and to be determined by chance, 'tis easy to arrive at a notion of a superior combination of chances. A dye that has four sides marked with a certain number of spots, and only two with another, affords us an obvious and easy instance of this superiority. The mind is here limited by the causes to such a precise

SECT.

XI.

Of the probability of

chances.

PART number and quality of the events; and, at the same time, is undetermined in its choice of any particular

Of event.

knowledge and Proceeding, then, in that reasoning, wherein we probability. have advanced three steps; that chance is merely the

negation of a cause, and produces a total indifference in the mind; that one negation of a cause and one to tal indifference can never be superior or inferior to another; and that there must always be a mixture of causes among the chances, in order to be the founda tion of any reasoning. We are next to consider what effect a superior combination of chances can have upon the mind, and after what manner it influences our judgment and opinion. Here we may repeat all the same arguments we employed in examining that belief which arises from causes; and may prove, after the same manner, that a superior number of chances produces our assent neither by demonstration nor probability. "Tis indeed evident, that we can never, by the comparison of mere ideas, make any discovery which can be of consequence in this affair, and that 'tis impossible to prove with certainty that any event must fall on that side were there is a superior number of chances. To suppose in this case any certainty, were to overthrow what we have established concerning the opposition of chances, and their perfect equality and indifference.

Should it be said, that though in an opposition of chances, 'tis impossible to determine with certainty on which side the event will fall, yet we can pronounce with certainty, that 'tis more likely and probable 'twill be on that side where there is a superior number of chances, than where there is an inferior: should this be said, I would ask, what is here meant by likelihood