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Of Probable or Experimental Reasoning.
IN N all our reasonings from the cause to the effect, we proceed on a fuppofition, and a belief, that the courfe of nature will continue to be in time to come what we experience it to be at prefent, and remember it to have been in time paft. This prefumption of continuance is the foundation of all our judgements concerning future events; and this, in many cafes, determines our conviction as effectually as any proof or demonstration whatsoever; although the conviction arifing from it be different in kind from what is produced by strict demonstration, as well as from thofe kinds of conviction that attend the evidence of fenfe, memory, and abstract intuition. The highest degree of conviction in reafoning from caufes to effects, is called moral certainty; and the inferior degrees refult from that fpecies of evidence which is called probability or verifimilitude. That all men will die; that the fun will rife to-morrow, and the fea ebb and flow; that
fleep will continue to refresh, and food to nourish us; that the fame articulate founds which to-day communicate the ideas of virtue and vice, meat and drink, man and beast, will to-morrow communicate the fame ideas to the fame persons, -no man can doubt, without being accounted a fool. In these, and in all other inftances where our experience of the past has been equally extenfive and uniform, our judgement concerning the future amounts to moral certainty: we believe, with full affurance, or at least without doubt, that the fame laws of nature which have hitherto operated, will continue to operate, as long as we foresee no cause to interrupt or hinder their operation.
But no perfon who attends to his own mind will fay, that, in these cafes, our belief, or conviction, is the effect of a proof, or of any thing like it. If reafoning be at all employed, it is only in order to give us a clear view of our paft experience with regard to the point in queftion. When this view is obtained, reasoning is no longer neceffary; the mind, by its own innate force, and in confequence of an irrefiftible and instinctive impulfe, infers the future from the past, immediately, and without the intervention of any argument. The fea has ebbed and flowed twice every day in time paft; therefore the fea will continue to ebb and flow twice every day in the time to come, is by no means
a logical deduction of a conclufion from premifes *
When our experience of the past has not been uniform nor extenfive, our opinion with regard to the future falls fhort of moral certainty; and amounts only to a greater or lefs degree of perfuafion, according to the greater or smaller proportion of favourable inftances: - we fay, fuch an event will probably happen, fuch another is wholly improbable. If a medicine has proved falutary in one instance, and hurtful in five, a phyfician would not chufe to recommend it, except in a defperate cafe; and would then confider its fuccefs as a thing rather to be wifhed than expected. An equal number of favourable and unfavourable inftances leave the mind in a state of fufpenfe, without exciting the smallest degree of affurance on either fide, except, perhaps, what may arise from our being more interested on the one fide than on the other. A physician influenced by fuch evidence would fay, “My pa"tient may recover, and he may die: I am forry to say, that the former event is not one whit more probable than the latter." When the favourable instances exceed the unfavourable in number, we begin to think the
* This remark was first made by Mr HUME. See it illuftrated at great length in his Effays, part 2. fect. 4. See alfo Dr Campbell's Differtation on Miracles, p. 13. 14. edit. 2.
future event in fome degree probable; and more or less fo, according to the furplus of favourable inftances. A few favourable inftances, without any mixture of unfavourable ones, render an event probable in a pretty high degree; but the favourable experience must be both extenfive and uniform, before it can produce moral certainty.
A man brought into being at maturity, and placed in a defert ifland, would abandon himself to despair, when he first saw the fun fet, and the night come on; for he could have no expectation that ever the day would be renewed. But he is transported with joy, when he again beholds the glorious orb appearing in the east, and the heavens and the earth illuminated as before. He again views the declining fun with apprehenfion, yet not without hope; the fecond night is lefs difmal than the firft, but is ftill uncomfortable, on account of the weakness of the probability produced by one favourable instance. As the infances grow more numerous, the probablity becomes ftronger and ftronger: yet may be queflioned, whether a man in theft circumftances would ever arrive at fo high a degree of moral certainty in this matter as we experience; who know, not only that the fun has rifen every day fince we began to exift, but also that the fame phenomenon has happened regularly for more than five thoufand years, without failing in a fingle inftance. The judgement of our great epic
poet appears no where to more advantage than in his eighth book; where Adam relates to the angel what paffed in his mind immediately after his awaking into life. The following paffage is at once tranfcendently beautiful, and philosophically just.
"While thus I call'd, and ftray'd I knew not "whither,
"From where I firft drew air, and first beheld
"This happy light, when anfwer none return'd,
"I then was passing to my former ftate Infenfible, and forthwith to diffolve *." Paradife Loft, b. 8. 1. 283.
Adam at this time had no experience of fleep, and therefore could not, with any probability, expect that he was to recover from it. Its approaches were attended with feelings fimilar to thofe he had experienced when awaking from non-existence, and would naturally fuggest that idea to his mind; and as he had no reafon to expect that his life was to continue, would intimate the probability
* The beauty of thefe lines did not efcape the elegant and judicious Addison; but that author does not affign the reafon of his approbation. Spect. N° 345.