We have seen what the process of belief in Propositions is. The subject and predicate, two names for the same thing, of which the predicate is either of the same extent with the subject, or of a greater extent, suggests, each of them, its meaning; that is, call up, by association, each of them, its peculiar cluster of ideas. Two clusters of ideas are called up in 433 connexion, and that a peculiar connexion, marked by the copula. To have two clusters of ideas, to know that they are two, and to believe that they are two, this is nothing more than three expressions for the same thing. To know that two clusters are two clusters, and to know that they are either the same, or different, is the same with having them. In this case, then, as in that of the belief of events, in sense and memory, the belief and the evidence are the same thing.
Belief of the conclusion of a syllogism, is preceded by two other beliefs. There is belief of the major proposition; belief of the minor proposition; by the process immediately above explained, in which the evidence and the belief are the same thing. These are the antecedent. There is, thirdly, belief of the conclusion, this is the consequent. The process of this belief has been so recently explained, that I do not think we need to repeat it. In this case, it is sometimes said, that the two premises are the evidence; sometimes it is said, that the ratiocination is the evidence; in the former of these applications of the word evidence, the belief of the concluding proposition of the syllogism is not included; in the last, it is. The ratiocination is the belief of all the three propositions; and, in this acceptation of the word, the evidence and the belief are not considered as two things, but one and the same thing. This, however, is only a difference of naming. About the particulars named, there is no room for dispute.[110]
[110] This chapter on Evidence is supplementary to the chapter on Belief, and is intended to analyse the process of weighing and balancing opposing grounds for believing.
434 Evidence is either of individual facts (not actually perceived by oneself), or of general truths. The former is the only case to which much attention is paid in the present chapter; which very happily illustrates it, by the case of navigators having to decide on the existence or non-existence of inhabitants in a newly discovered island. The process of balancing the evidence for and against, is depicted in a very lively manner. Let us see whether the mental facts set down in the exposition, are precisely those which take place.
When the sailors have seen prints of a foot, resembling those of a man, the idea is raised of a man making the print. When they afterwards see a monkey, whose feet leave traces almost similar, the idea is also raised of a monkey making the print, and the state of their minds, the author says, is doubt. Of this state he gives the following analysis: “There is here a double association with the print of the foot. There is the association of a man, and there is the association of a monkey. First, the print raises the idea of a man, but the instant it does so, it raises also the idea of a monkey. The idea of the monkey, displacing that of the man, hinders the first association from the fixity which makes it belief; and the idea of man, displacing that of monkey, hinders the second association from that fixity which constitutes belief.”
This passage deserves to be studied; for without having carefully weighed it, we cannot be certain that we are in complete possession of the author’s theory of Belief.
There are two conflicting associations with the print of the foot. The picture of a man making it, cannot co-exist with that of a monkey making it. But the two may alternate with one another. Had the association with a man been the only association, it would, or might (for on this point the author is not explicit) have amounted to belief. But the idea of the monkey and that of the man alternately displacing one another, hinder either association from having the fixity which would make it belief.
This alternation, however, between the two ideas, of a monkey making the footprint and of a man making it, may 435 very well take place without hindering one of the two from being accompanied by belief. Suppose the sailors to obtain conclusive evidence, testimonial or circumstantial, that the prints were made by a monkey. It may happen, nevertheless, that the remarkable resemblance of the foot prints to those of a man, does not cease to force itself upon their notice: in other words, they continue to associate the idea of a man with the footsteps; they are reminded of a man, and of a man making the footsteps, every time they see or think of them. The double association, therefore, may subsist, and the one which does not correspond with the fact may even be the most obtrusive of the two, while yet the other conception may be the one with which the men believe the real facts to have corresponded.
All the rest of the exposition is open to the same criticism. The author accounts very accurately for the presence of all the ideas which the successive appearance of the various articles of evidence arouses in the mind. But he does not shew that the belief, which is ultimately arrived at, is constituted by the expulsion from the mind of one set of these ideas, and the exclusive possession of it by the other set. It is quite possible that neither of the associations may acquire the “fixity” which, according to the apparent meaning of the author, would defeat the other association altogether, and drive away the conception which it suggests; and yet, one of the suppositions may be believed and the other disbelieved, according to the balance of evidence, as estimated by the investigator. Belief, then, which has been already shewn not to require an inseparable association, appears not to require even “fixity”—such fixity as to exclude the idea of the conflicting supposition, as it does exclude the belief.
The problem of Evidence divides itself into two distinguishable enquiries: what effect evidence ought to produce, and what determines the effect that it does produce: how our belief ought to be regulated, and how, in point of fact, it is regulated. The first enquiry—that into the nature and probative force of evidence: the discussion of what proves what, and 436 of the precautions needed in admitting one thing as proof of another—are the province of Logic, understood in its widest sense: and for its treatment we must refer to treatises on Logic, either inductive or ratiocinative. All that would be in place here, reduces itself to a single principle: In all cases, except the case of what we are directly conscious of (in which case, as the author justly observes, the evidence and the belief are one and the same thing)—in all cases, therefore, in which belief is really grounded on evidence, it is grounded, in the ultimate result, on the constancy of the course of nature. Whether the belief be of facts or of laws, and whether of past facts or of those which are present or future, this is the basis on which it rests. Whatever it is that we believe, the justification of the belief must be, that unless it were true, the uniformity of the course of nature would not be maintained. A cause would have occurred, not followed by its invariable effect; an effect would have occurred, not preceded by any of its invariable causes; witnesses would have lied, who have always been known to speak the truth; signs would have proved deceptive, which in human experience have always given true indication. This is obvious, whatever case of belief on evidence we examine. Belief in testimony is grounded on previous experience that testimony is usually conformable to fact: testimony in general (for even this may with truth be affirmed); or the testimony of the particular witness, or the testimony of persons similar to him. Belief that the sun will rise and set to-morrow, or that a stone thrown up into the air will fall back, rests on experience that this has been invariably the case, and reliance that what has hitherto occurred will continue to occur hereafter. Belief in a fact vouched for by circumstantial evidence, rests on experience that such circumstances as are ascertained to exist in the case, never exist unaccompanied by the given fact. What we call evidence, whether complete or incomplete, always consists of facts or events tending to convince us that some ascertained general truths or laws of nature must have proved false, if the conclusion which the evidence points to is not true.