Notes on Hume's Treatise
by G. J. Mattey
PART III. OF KNOWLEDGE AND PROBABILITY
§ XIII. Of unphilosophical probability.
Some other forms of probable reasoning have the same pedigree as those just discussed, i.e., probability of chances and of causes. These are not accorded the same respect by philosophers, who regard the latter as "reasonable foundations of belief and opinion." So Hume calls these "unphilosophical probability"
1. If an argument is based on something we remember, it decreases in conviction with time. But the philosophers think that an argument should have the same persuasive value forever. They are wrong, because "according to the foregoing system," belief is a matter of the liveliness of ideas, and this liveliness in fact varies with the vivacity of the original perception from which the idea arises.
2. The converse also holds. Livelier impressions produce greater assurance than fainter ones, as in the case of a recent observation. (The drunkard has recently seen one of his comrades die from drinking and for a time dreads meeting the same fate.)
3. Hume had distinguished between proofs and probabilities, where proofs admit of no doubt, while probability admits of some doubt. But proofs can become probabilities. Chains of reasoning can lead to loss of force with distance from the original premises. So there may have been proof earlier in the proof, but because of the diminishing intensity of the ideas, they lose their convincingness. Hume observes that a long demonstration can produce a result weaker even than the conclusions of a recent probable reasoning. "One must have a very strong and firm imagination to preserve the evidence to the end, where it passes thro' so many stages."
The fact that many steps in reasoning leads to decay raises a curious phenomenon: ancient history. Why doesn't it fade away, if belief is founded in vivacity? Why is it not the case that "the evidence of all antient history must now be lost" or will some day be lost? We all believe that the evidence will not be lost, however. This seems a counter-example to the account of belief as vivacity.
This leads to an important point, that if all evidence for the Christian religion were probable, then there must be diminution over time, to the point of extinction. (Hume denies, however, that the antecedent holds.) Hume allows that the principle of the diminution of probabilities is "true in general," with an important exception to be discussed in the first section of the next part. The exception is the case where one considers the probabilities of probabilities, etc. In that case, the imagination gets strained early on, not giving the probabilities a chance to diminish.
Now suppose that instead of probabilities we begin with proof. The solution is that in the process of passing the information on, all the links are of the same kind, based on the fidelity of printers and copyists. All steps are the same, so there is no reason for diminution. If the means of transmission were heterogeneous, degeneration would occur. "But as most of the proofs are perfectly resembling, the mind runs easily along them, jumps from one part to another part with facility, and forms but a confus'd and general notion of each link."
4. PREJUDICE comes from rashly formed general rules. We reason according to them (an Irishman cannot have wit, though a conversation with one may be very agreeable) "in spite of sense and reason. Human nature is very subject to errors of this kind; and perhaps this nation as much as any others."
So why, then, do we form general rules, if they can result in contradiction of present observation and experience? For the same reason as we form other judgments with respect to cause and effect: habit and experience. The imagination operates when ideas are similar though not identical, though it does so to an inferior degree. This is how Hume explained the use of arguments from analogy. There is a decay in force, to be sure, but some force remains.
In some cases, "superfluous circumstances are numerous, and remarkable, and frequently conjoin'd with the essential," so that even without the essential the mind is carried to conviction. This can be corrected, but it remains that "custom takes the start, and gives a biass to the imagination."
An example of this is of a man suspended in a solid cage who trembles. The imagination runs away, thinking of "the ideas of fall, descent, and harm and death," which are derived from custorm. The circumstance of solidity is not enough to overcome this, though it "ought to give hima a perfect security." and excites a passion, and this reinforces the imagination, forming a feedback loop: "both his fancy and affections, thus mutually supporting each other, cause the whole to have a very great influence upon him."
No further examples are needed. Judgment and imagination can never be opposed, it seems, since both are the product of custom. The exception is through the use of general rules which allow us to distinguish the accidental circumstances from efficacious causes [see Section 15]. When there is a clash between general rules and the exceptions to these rules conjured up in the imagination, we attribute the general rule to judgment "as being more extensive and constant," while the exception is attributed to the imagination, "as being more capricious and uncertain."
General rules seem to be in opposition to each other. What happens is that we have an idea which resembles a cause but which may be "different in the most material and most efficacious circumstances from that cause." But this act of the mind is found, upon review, to be of an irregular nature, and so it is rejected. The vulgar are prone to the first kind of use of general rules and the wise man to "the most establish'd principles of reasoning," which often contradict the first kind. The skeptic has a field day here, because only general rules, which are unphilosophical species of reasoning, can be used to counter the use of general rules and other unphilosophical probabilities. The skeptic observes "a new and signal contradiction in our reason." "The following of general rules is a very unphilosophical species of probability, and yet 'tis only by following them that we can correct this, and all other unphilosophical probabilities."
General rules' effects increase when conjoined to the judgment. Hume illustrates this by noting that the passions are not aroused so much by indirect insult as by direct.
The only difference between the two cases is that the signs used in the insult are "general and universal" in the direct case and "more singular and uncommon" in the indirect. In the former case, the movement of the imagination takes place with greater facility, so that the object is conceived with greater force. The fact that it is a greater mark of respect to insult people indirectly than directly confirms the difference. There is an analogy here with ideas and impressions, and ideas produced by general connections and those produced by particular ones, respectively.
A possible counter-example is scurrility [coarseness and indecency of language], which is more direct than delicate satire but less displeasing. The reason for its relative lack of effect is that it turns against itself, in we have a just reason to blame the person who injures us. But it is explained by the same principle. It was originally more disagreeable due to the "palpable and undeniable" general rules about breeding. Then "it becomes less disagreeable because it originally was more so." That is, the very same rules of good breeding cause us to recognize the vulgarity of the person who does it, thus reducing our displeasure.
An analogous phenomenon is the way that we overlook obvious vices when they are committed discreetly. There is the same idea but a difference in the manner of presentation.
The difference between "the open and conceal'd violations of the laws of honor" is that in the first case, the sign is single and sufficient for our reasoning, while in the second, the "signs are numerous, and decide little or nothing when alone and unaccompany's with many minute circumstances, whic hare almost imperceptible." Reasoning is the more convincing as it is "the more single and united . . . to the eye, and the less exercise it gives to the imagination. . . ."
The observations of Cardinal de Retz are also explained: "that there are many things in which the world wishes to be deceiv'd" and "that it more easily excuses a person in acting than in talking contrary to the decorum of his profession and character." In the second case, the words are more openly and distinctively signs of the transgression, while action can be explained by myriad circumstances.
Hume now draws a conclusion from much of the above: "It appears upon the whole, that every kind of opinion or judgment, which amounts not to knowledge, is deriv'd entirely from the force and vivacity of the perception, and that these qualities constitute I nthe mind, what we call the BELIEF of the existence of any object." Memory gives the most vivid perceptions, and hence is most trusted. Cause and effect produces less, but still great vivacity, when we have perfect constancy. Lesser degrees of evidence are many:
The system Hume has presented has its parts founded on "undoubted arguments," the parts agree with one another, and each is needed to explain the other. This is what "principally gives authority to this system." The explanation of probability is recapitulated: the side with superior instances gives a vivacity which is diminished by contrary instances. At last, the larger collection of possibilities prevails, with a force proportional to its superiority. Without attributing these judgments to the effects of custom on the imagination, "we lose ourselves in perpetual contradiction and absurdity."
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