A Treatise of Human Nature. David Hume
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to us in all the colours of eloquence; and the vivacity produced by the fancy is in many cases greater than that which arises from custom and experience. We are hurried away by the lively imagination of our author or companion; and even he himself is often a victim to his own fire and genius.
Nor will it be amiss to remark, that as a lively imagination very often degenerates into madness or folly, and bears it a great resemblance in its operations; so they influence the judgment after the same manner, and produce belief from the very same principles. When the imagination, from any extraordinary ferment of the blood and spirits, acquires such a vivacity as disorders all its powers and faculties, there is no means of distinguishing betwixt truth and falshood; but every loose fiction or idea, having the same influence as the impressions of the memory, or the conclusions of the judgment, is received on the same footing, and operates with equal force on the passions. A present impression and a customary transition are now no longer necessary to enliven our ideas. Every chimera of the brain is as vivid and intense as any of those inferences, which we formerly dignifyed with the name of conclusions concerning matters of fact, and sometimes as the present impressions of the senses.
We may observe the same effect of poetry in a lesser degree; and this is common both to poetry and madness, that the vivacity they bestow on the ideas is not derived from the particular situations or connexions of the objects of these ideas, but from the present temper and disposition of the person. But how great soever the pitch may be, to which this vivacity rises, it is evident, that in poetry it never has the same feeling with that which arises in the mind, when we reason, though even upon the lowest species of probability. The mind can easily distinguish betwixt the one and the other; and whatever emotion the poetical enthusiasm may give to the spirits, it is still the mere phantom of belief or persuasion. The case is the same with the idea, as with the passion it occasions. There is no passion of the human mind but what may arise from poetry; though at the same time the feelings of the passions are very different when excited by poetical fictions, from what they are when they are from belief and reality. A passion, which is disagreeable in real life, may afford the highest entertainment in a tragedy, or epic poem. In the latter case, it lies not with that weight upon us: It feels less firm and solid: And has no other than the agreeable effect of exciting the spirits, and rouzing the attention. The difference in the passions is a clear proof of a like difference in those ideas, from which the passions are derived. Where the vivacity arises from a customary conjunction with a present impression; though the imagination may not, in appearance, be so much moved; yet there is always something more forcible and real in its actions, than in the fervors of poetry and eloquence. The force of our mental actions in this case, no more than in any other, is not to be measured by the apparent agitation of the mind. A poetical description may have a more sensible effect on the fancy, than an historical narration. It may collect more of those circumstances, that form a compleat image or picture. It may seem to set the object before us in more lively colours. But still the ideas it presents are different to the feeling from those, which arise from the memory and the judgment. There is something weak and imperfect amidst all that seeming vehemence of thought and sentiment, which attends the fictions of poetry.
We shall afterwards have occasion to remark both the resemblance and differences betwixt a poetical enthusiasm, and a serious conviction. In the mean time I cannot forbear observing, that the great difference in their feeling proceeds in some measure 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 encrease 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. It is 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. It is 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 and images, which have their effect upon the poet himself, as well as upon his readers.
SECT. 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 comparison of ideas, are obliged to comprehend all our arguments 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; it is 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 it is only probable the sun will rise to-morrow, or that all men must dye; though it is plain we have no further assurance of these facts, than what experience affords us. For this reason, it would perhaps be more convenient, in order at once to preserve the common signification of words, and mark the several degrees of evidence, to distinguish human reason into three kinds, viz. THAT FROM KNOWLEDGE, FROM PROOFS, AND FROM PROBABILITIES. By knowledge, I mean the assurance arising from the comparison of ideas. By proofs, those arguments, 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. It is this last species of reasoning, I proceed to examine.
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 iii 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 it is 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, it is instantly re-instated.
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