I think perhaps the strongest argument on Hume’s side is to be derived from the character of causal laws in physics. It appears that simple rules of the form “A causes B” are never to be admitted in science, except as crude suggestions in early stages. The causal laws by which such simple rules are replaced in well-developed sciences are so complex that no one can suppose them given in perception; they are all, obviously, elaborate inferences from the observed course of nature. I am leaving out of account modern quantum theory, which reinforces the above conclusion. So far as the physical sciences are concerned, Hume is wholly in the right: such propositions as “A causes B” are never to be accepted, and our inclination to accept them is to be explained by the laws of habit and association. These laws themselves, in their accurate form, will be elaborate statements as to nervous tissue–primarily its physiology, then its chemistry, and ultimately its physics.
The opponent of Hume, however, even if he admits the whole of what has just been said about the physical sciences, may not yet admit himself decisively defeated. He may say that in psychology we have cases where a causal relation can be perceived. The whole conception of cause is probably derived from volition, and it may be said that we can perceive a relation, between a volition and the consequent act, which is something more than invariable sequence. The same might be said of the relation between a sudden pain and a cry. Such views, however, are rendered very difficult by physiology. Between the will to move my arm and the consequent movement there is a long chain of causal intermediaries consisting of processes in the nerves and muscles. We perceive only the end terms of this process, the volition and the movement, and if we think we see a direct causal
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connection between these we are mistaken. This argument is not conclusive on the general question, but it shows that it is rash to suppose that we perceive causal relations when we think we do. The balance, therefore, is in favour of Hume’s view that there is nothing in cause except invariable succession. The evidence, however, is not so conclusive as Hume supposed.
Hume is not content with reducing the evidence of a causal connection to experience of frequent conjunction; he proceeds to argue that such experience does not justify the expectation of similar conjunctions in the future. For example: when (to repeat a former illustration) I see an apple, past experience makes me expect that it win taste like an apple, and not like roast beef; but there is no rational justification for this expectation. If there were such a justification, it would have to proceed from the principle “that those instances, of which we have had no experience, resemble those of which we have had experience.” This principle is not logically necessary, since we can at least conceive a change in the course of nature. It should therefore be a principle of probability. But all probable arguments assume this principle, and therefore it cannot itself be proved by any probable argument, or even rendered probable by any such argument. “The supposition, that the future resembles the past, is not founded on arguments of any kind, but is derived entirely from habit. * The conclusion is one of complete scepticism:
“All probable reasoning is nothing but a species of sensation. ‘Tis not solely in poetry and music, we must follow our taste and sentiment, but likewise in philosophy. When I am convinced of any principle, ’tis only an idea, which strikes more strongly upon me. When I give the preference to one set of arguments above another, I do nothing but decide from my feeling concerning the superiority of their influence. Objects have no discoverable connexion together; nor is it from any other principle but custom operating upon the imagination, that we can draw
any inference from the appearance of one to the existence of another.” â€
The ultimate outcome of Hume’s investigation of what passes for knowledge is not what we must suppose him to have desired. The sub-title of his book is: “An attempt to introduce the experimental
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* Book I, Part III, Sec. IV.
€ Book I, Part III, Sec. VIII.
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method of reasoning into moral subjects.” It is evident that he started out with a belief that scientific method yields the truth, the whole truth, and nothing but the truth; he ended, however, with the conviction that belief is never rational, since we know nothing. After setting forth the arguments for scepticism (Book I, Part IV, Sec. I), he goes on, not to refute the arguments, but to fall back on natural credulity.
“Nature, by an absolute and uncontrollable necessity has determined us to judge as well as to breathe and feel; nor can we any more forbear viewing certain objects in a stronger and fuller light, upon account of their customary connexion with a present impression, than we can hinder ourselves from thinking as long as we are awake, or seeing the surrounding bodies, when we turn our eyes towards them in broad sunshine. Whoever has taken the pains to refute this total scepticism, has really disputed without an antagonist, and endeavoured by arguments to establish a faculty, which nature has antecedently implanted in the mind, and rendered unavoidable. My intention then in displaying so carefully the arguments of that fantastic sect, is only to make the reader sensible of the truth of my hypothesis, that all our reasonings concerning causes and effects are derived from nothing but custom; and that belief is more properly an act of the sensitive, than of the cogitative part of our natures.”
“The sceptic,” he continues (Book I, Part IV, Sec. II), “still continues to reason and believe, even though he asserts that he cannot defend his reason by reason; and by the same rule he must assent to the principle concerning the existence of body, tho’ he cannot pretend by any arguments of philosophy to maintain its veracity . . . We may well ask, what causes us to believe in the existence of body? But ’tis vain to ask, whether there be body or not? That is a point, which we must take for granted in all our reasonings.”
The above is the beginning of a section “Of scepticism with regard to the senses.” After a long discussion, this section ends with the following conclusion:
“This sceptical doubt, both with respect to reason and the senses, is a malady, which can never be radically cured, but must return upon us every moment, however we may chase it away, and sometimes may seem entirely free from it. . . . Carelessness and inattention alone can afford us any remedy. For this reason I rely entirely
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upon them; and take it for granted, whatever may be the reader’s opinion at this present moment, that an hour hence he will be persuaded there is both an external and internal world.”
There is no reason for studying philosophy–so Hume maintains-except that, to certain temperaments, this is an agreeable way of passing the time. “In all the incidents of life we ought still to preserve our scepticism. If we believe, that fire warms, or water refreshes, ’tis only because it costs us too much pains to think otherwise. Nay if we are philosophers, it ought only to be upon sceptical principles, and from an inclination, which we feel to be employing ourselves after that manner.” If he abandoned speculation, “I feel I should be a loser in point of pleasure; and this is the origin of my philosophy.”
Hume’s philosophy, whether true or false, represents the bankruptcy of eighteenth-century reasonableness. He starts out, like Locke, with the intention of being sensible and empirical, taking nothing on trust, but seeking whatever instruction is to be obtained from experience and observation. But having a better intellect than Locke’s, a greater acuteness in analysis, and a smaller capacity for accepting comfortable inconsistencies, he arrives at the disastrous conclusion that from experience and observation nothing is to be learnt. There is no such thing as a rational belief: “If we believe that fire warms, or water refreshes, ’tis only because it costs us too much pains to think otherwise.” We cannot help believing, but no belief can be grounded in reason. Nor can one line of action be more rational than another, since all alike are based upon irrational convictions. This last conclusion, however, Hume seems not to have drawn. Even in his most sceptical chapter, in which he sums up the conclusions of Book I, he says: “Generally speaking, the errors in religion are dangerous; those in philosophy only ridiculous.” He has no right to say this. “Dangerous” is a causal word, and a sceptic as to causation cannot know that anything is “dangerous.”
In fact, in the later portions of the Treatise, Hume forgets all about his fundamental doubts, and writes much as any other enlightened moralist of his time might have written; he applies to his doubts the remedy that he recommends, namely “carelessness and inattention.” In a sense, his scepticism is insincere, since he cannot maintain
