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Robable Evidence is essentially distinguished from demonstrative by this, that
it admits of Degrees; and of all Va. riety of them, from the highest moral Certainty, to the very lowest Presumption. We. cannot indeed say a thing is probably true upon one very slight Presumption for it ; because, as there may be Probabilities on both sides of a Question, there may be fome against it: and though there be not, yet a flight Presumption does not beget that Degree of Conviction, which is implied in saying a thing is probably true. But that the flightest poffible Presumption is of the nature of a Probability, appears from hence; that such low Presumption often repeated, will amount even to moral Certainty. Thus a Man's having observed the Ebb and Flow of the Tide to Day, affords some sort of Presumption, though the lowest imaginable, that it may happen again to Morrow: But the Observation of this Event for so many Days, and Months, and Ages together, as it has been observed by
Mankind, gives us a full Assurance that it will.
That which chiefly constitutes Probability is expressed in the Word Likely, i. e. like fome Truth a, or true Event; like it, in itself, in its Evidence, in some more or fewer of its Circumstances. For when we deter- . mine a thing to be probably true, suppose that an Event has or will come to pass, 'tis from the Mind's remarking in it a Likeness to some other Event, which we have observed has come to pass. And this Observation forms, in numberless daily Instances, a Presumption, Opinion, or full Conviction, that such Event has or will come to pass; according as the Observation is, that the like Event has some. times, most commonly, or always so far as our Observation reaches, come to pass at like Distances of Time, or Place, or upon
like Occasions. Hence arises the Belief, that a Child, if it lives twenty years, will grow up to the Stature and Strength of a Man; that Food will contribute to the preservation of its Life, and the Want of it for such a Number of days, be its certain Destruction. So likewise the Rule and Measure of our Hopes and Fears concerning the Success of our Pursuits ; our Expectations that Others will act fo and so in such Circumstances; and our Judgment a Verisimile.
that such Actions proceed from such Princis ples; all These rely upon cur having obser: ved the like to what we hope, fear, expect, judge; I say upon our having observed the like, either with respect to Others or Ourselves. And thus, whereas the Prince bwho had always lived in a warm Climate, naturally con: cluded in the
way of Analogy, that there was no such thing as Water’s becoming hard; because he had always observed it to be fluid and yielding: We on the contrary,
from Analogy conclude, that there is no Presumption at all against This : that 'tis supposeable, there may be Frost in England any given Day in January next; probable that there will on some Day of the Month; and that there is a moral Certainty, i. e. Ground for an Expectation without any Doubt of it, in fome Part or other of the Winter,
Probable Evidence, in its very Nature, afs fords but an imperfect kind of Information ; and is to be considered as relative only to Beings of limited Capacities. For Nothing which is the possible object of Knowledge, whether past, present, or future, can be probable to an infinite Intelligence; since it cannot but be discerned absolutely as it is in itself,
• The Story is told by Mr. Locke in the Chapter of Proba
certainly true, or certainly false. But to Us, Probability is the very Guide of Life.
From these things it follows, that in Questions of Difficulty, or such as are thought so, where more satisfactory Evidence cannot be had, or is not seen ; if the Result of Examination be, that there
the whole, any the lowest Presumption on one side, and none on the other, or a greater Presumption on One side, though in the lowest Degree greater; this determines the Question, even in matters of Speculation; and in matters of Practice, will lay us under an absolute and formal Obligation, in point of Prudence and of Interest, to act upon that Presumption or low Probability, though it be so low as to leave the Mind in very great Doubt which is the Truth. For surely a Man is as really bound in Prudence, to do what upon the whole appears, according to the best of his Judgment, to be for his Happiness, as what he certainly knows to be fo. Nay further, in Questions of great Consequence, a reasonable Man will think it concerns him to remark lower Probabilities and Presumptions than these ; such as amount to no more than showing One side of a Question to be as supposeable and credible as the Other : nay such as but amount to much less even than this. For numberless Instances might be mentioned
respecting respecting the common Pursuits of Life, where a Man would be thought, in a literal Sense, distracted, who would not act, and with great Application too, not only upon an even Chance, but upon much less, and where the Probability or Chance was greatly against his lucceeding
It is not my Design to enquire further into the Nature, the Foundation, and Measure of Probability; or whence it proceeds that Likeness should beget that Presumption, Opinion, and full Conviction, which the human Mind is formed to receive from it, and which it does necessarily produce in every one; or to guard against the Errors, to which Reasoning from Analogy is liable. This belongs to the Subject of Logick; and is a Part of that Subject which has not yet :been thoroughly considered. Indeed I shall not take upon me to say, how far the Extent, Compass, and Force, of analogical Reasoning, can be reduced to general Heads and Rules; and the Whole be formed into a System. But though so little in this Way has been attempted by those who have treated of our intellectual Powers, and the Exercise of them ; this does not hinder but that we may be, as we unquestionably are, assured, that Analogy is of Weight, in various Degrees, towards determining our Judgment, See Chap. vi. Part II.