G. J. Mattey’s Notes on Hume’s Treatise, Book 1, Part 3, Section 15

Notes on Hume’s Treatise

by G. J. Mattey

Book 1
Of the UNDERSTANDING
PART 3
Of knowledge and probability, &c.

Sect. 15. Rules by which to judge of causes and effects.

Having completed his treatment of the idea of a necessary connection, and thus his account of causal relations, the author returns to the examination of causal reasoning, which had been discussed in Section 12, which concerned how we reason causally in the face of contrary causes. He lays down eight general rules for causal reasoning. These rules seem to be what the author had referred to in Section 13, paragraphs 11 and 12 as being reflective and typical of wisdom, in contrast to certain “unphilosophical” general rules of the vulgar.

As the author’s treatment of the causal relation is unique to him, his rules are for the most part original to him. Perhaps the closest resemblance between the author’s rules and earlier rules for judging cause and effect is to Newton’s “Rules of Reasoning in Philosophy.”

1. The author’s doctrine precludes determining whether a given object is or is not a cause of any other object by merely surveying the objects themselves, “without consulting experience.” [This doctrine is first stated in Section 1, paragraph 1, where it is stated that, “as the power, by which one object produces another is never discoverable merely from their ideas, ’tis evident cause and effect are relations, of which we receive information from experience, and not from any abstract reasoning or reflection.” Arguments for this doctrine are given in Section 2, paragraph 5, and in Section 6, paragraph 1.] So anything might produce anything else. “Creation, annihilation, motion, reason, volition; all these may arise from one another, or from any other object we can imagine.” This follows from the following two principles:

2.Given the possibility of any object being the cause or effect of any other [given priority and contiguity], “it may be proper to fix some general rules, by which we may know when they really are so.”

3. Rule #1. The cause and effect must be contiguous in space and time. [See Section 2, paragraph 6.]

5. Rule #3. There must be a constant union between the objects of the same kind as the cause and those of the same kind as the effect. [See Section 6, paragraph 3] “’Tis chiefly this quality, that constitutes the relation.”

6. Rule #4. Once established, causal relations may be taken to hold without exception: “The same cause always produces the same effect, and the same effect never arises but from the same cause.” After the causal relation has been established by constant conjunction or some other “experiment” [as described in Section 8, paragraph 14], “we immediately extend our observation to every phænomenon of the same kind, without waiting for that constant repetition, from which the first idea of this relation is deriv’d.” This empirical principle “is the source of most of our philosophical reasonings.”

7. Rule #5. If an effect is caused by several objects with a common quality, it is that quality which produces the effect. This rule is said to “hang on” Rule #4. According to that rule, if there is more than one effect of the same kind, their causes are of the same kind. This kind is what is found to be resembling in the cause. And what is resembling is the common quality of the objects. Thus, we must locate the causal factor in the objects in the common quality we discover in them.

8. Rule #6. If two resembling objects differ in their effects, they were the result of different causes. This rule likewise is derived from Rule #4. Given that like causes produce like effects, it follows that unlike effects are produced by unlike causes. So, if we find two like objects that produce different effects, we must conclude that “this irregularity” is due to the fact that they are unlike in some relevant way.

9. Rule #7. If there is a correlation between the increase or diminution in an effect and in its [compound] cause, the effect is a compound one in which the parts of the effect are caused by parts of the cause. [This rule had been announced in Section 12, paragraph 16, as “a certain maxim” that applies in both moral and natural philosophy.] We suppose that the presence or absence of one part of the cause is constantly conjoined to the presence or absence of one part of the effect that is proportionate to it. In that case, the part of the cause is the cause of the corresponding part of the effect. The author cautions that we must be careful not to apply this rule given only “a few experiments.” Apparently, the problem would lie in concluding that the condition for applying the rule holds. So, there is a correlation in some instances with an increase in heat with an increase of pleasure, but if an object gets too hot, the pleasure “degenerates into pain.” So in such a case, the correlation is imperfect.

10. Rule #8. If an object exists for any period of time “in its full perfection” without any effect, it requires the assistance of another cause to bring about its effect. [This rule was used in Section 2, paragraph 7, in the argument that the causal relation requires that the cause be temporally prior to the effect. To the extent that the priority of the cause depends on this rule, Rule #2 depends on it.] The argument appeals to a principle that appears to be a version of Rule #4, that “like effects necessarily follow from like causes.” Let us suppose that an object A exists for a time “in its complete perfection” without causing B. Let us suppose as well that to exist in complete perfection is to have every quality it could have in order to bring about B. Suppose further that B is in fact caused at a subsequent time, say at time t₁. Then the qualities A had before t₁ were not sufficient to cause B, since the qualities that A had before t₁ would have caused it before then, had they been sufficient. This seems to be the import of the appeal to Rule #4, that like effects necessarily follow from like causes. So if the effects are unlike, the causes must be as well. If B is caused later and not before t₁, there had to have been something different in its cause from what was in A. The only thing this different thing could have been is the assistance of “some other principle, which may forward its [A’s] influence and operation.”

11. These general rules for judging cause and effect are enough “LOGIC” for the author’s present purposes. In fact, he might even have dispensed with them altogether and relied on the “natural principles of the understanding.” The long rule-sets produced by the scholastic philosophers give them no advantage over the vulgar in doing philosophy. In fact, the rules for philosophizing “are very easy in their invention.” However, they are very difficult to apply, even in “experimental philosophy” [apparently here meaning natural philosophy, as there is later drawn a contrast with moral philosophy]. This requires “the utmost stretch of human judgment.” The problem is the complexity of nature, which makes it difficult to distinguish the parts of objects and apply the rules to them properly. Not only must we find the “essential” [causally efficacious] parts, but we also must perform new experiments to justify the claim that they are essential. And these new experiments raise the same question. So we need to be extremely careful and persevering in our investigations, as well as exercising “the utmost sagacity to choose the right way among so many that present themselves.” The situation is even worse in moral philosophy. Here we find “a much greater complication of circumstances, and [that] those views and sentiments, which are essential to any action of the mind, are so implicit and obscure, that they often escape our strictest attention, and are not only unaccountable in their causes, but even unknown in their existence.” The author fears that this observation will be seen as an excuse for the small amount of success he has attained in moral philosophy.

12. The author finds that the only solution to the problem of understanding the workings of the mind is to enlarge the sphere of his “experiments” and examine the reasoning faculty of animals. [If it can be found that its operations are similar to those of humans, he can be more confident in his claims about the reasoning faculty of humans.]

There is no corresponding set of general rules for causal reasoning in the Enquiry.