An Enquiry Concerning Hume's Misunderstanding Bryan Caplan Tu 3-4 Phil 122 Question #1 1. Introduction Remarkably, it is possible to sum up David Hume's vital assumptions about reasoning in a single proposition: Reason does NOTHING except locate the presence or absence of contradictions. This paper will attempt three tasks: first, to show the textual support for my interpretation; second, to explain how Hume's skepticism about induction depends on this assumption; and third, to briefly argue that Hume's basic assumption is wrong. 2. Textual Support Whenever Hume wants to show that reasoning cannot support something, he uses the same argument: the alternative is not a contradiction. "The contrary of every matter of fact is still possible; because it can never imply a contradiction, and is conceived by the mind with the same facility and distinctness, as if ever so conformable to reality. We should in vain, therefore, attempt to demonstrate its falsehood. Were it demonstratively false, it would imply a contradiction, and could never be distinctly conceived by the mind."1 Suppose that we try to use reason to establish any matter of fact. Hume says that our effort is futile, because the alternative is conceivable. But if the alternative is conceivable, then it is not a contradiction, because contradictions are inconceivable. But reason can refute something only if it is a contradiction. Hence, reason can never establish any matter of fact. Hume liberally repeats this argument throughout his works on epistemology. When he denies that reason justifies the law of cause-and-effect, he says, "That there are no demonstrative arguments in this case, seems evident; since it implies no contradiction, that the course of nature may change."2 The argument is the same as above: An alternative is conceivable; contradictions are not conceivable; and reason can only demonstrate that something is false if it is a contradiction. Hence, reason cannot establish the law of cause-and-effect. Hume uses the same argument in A Treatise of Human Nature. "There is no object, which implies the existence of any other if we consider the objects in themselves. Such an inference wou'd amount to knowledge, and wou'd imply the absolute contradiction and impossibility of conceiving any thing different."3 Once again, Hume notes that he can conceive of one object without a second object. Since no contradictions are conceivable, this is not a contradiction. And since reason does nothing but locate the presence or absence of contradictions, reason cannot establish a connection between any two things. Later in the Treatise, Hume makes the argument still more explicit: "To form a clear idea of any thing, is an undeniable argument for its possibility, and is alone a refutation of any pretended demonstration against it."4 Conceivability implies the absence of a contradiction, and the absence of a contradiction implies that reason has nothing to say on the matter. To cement my interpretation, let us turn to Hume's Abstract of a Treatise of Human Nature, where he repeats the argument. "The mind can always conceive any effect to follow from any cause, and indeed any event to follow upon another: whatever we conceive is possible, at least in a metaphysical sense: but wherever a demonstration takes place, the contrary is impossible, and implies a contradiction. There is no demonstration, therefore, for any conjunction of cause and effect."5 As always, his argument flows from the conceivability of an alternative, to the absence of a contradiction, to the forced silence of reason on the question. "What is demonstratively false implies a contradiction; and what implies a contradiction cannot be conceived."6 Hume could hardly be more explicit. In all three works, he uses precisely the same argument. And this argument rests on a crucial assumption about reason and reasoning: namely, that reason does nothing except locate the presence or absence of contradictions. While Hume may be open to interpretation on some points, the textual support for my claim is quite solid: it spans at least three of his epistemological works, and appears repeatedly in each. The next section explains in detail why this assumption about reasoning matters. 3. The Crucial Assumption Let us formally state the argument that Hume uses above in order to see why his assumption crucially supports his view that we never have any reason to believe any matter of fact. 1. The alternative to any matter of fact is conceivable. 2. If something is conceivable, then it is not a contradiction. 3. Reason does nothing except locate the presence or absence of contradictions. Therefore, reason has nothing to say about any matter of fact; if a proposition concerns matters of fact, reason can neither support nor refute it. It is hard to doubt premises #1 and #2. We can indeed conceive of alternatives to any matter of fact. And it seems like a basic feature of a contradiction that it is inconceivable. (Try to conceive of a circular square. Now try to conceive that gremlins exist. Notice the difference?) Premise #3 is therefore the crucial step in the argument -- and Hume's most central assumption about reasoning. How does the above argument relate to Hume's argument that we never have any reason to believe any unobserved matter of fact? I shall briefly but formally state Hume's argument against induction, then see how it relates to his central assumption about reasoning. 1. All knowledge comes either from observation or reason. 2. Knowledge of unobserved matters of fact can't come from reason, because the alternative to any matter of fact is conceivable and therefore implies no contradiction. 3. Knowledge of unobserved matters of fact can be derived from knowledge of observed matters of fact only if the law of cause-and-effect is known. 3a. Reason cannot establish the law of cause-and-effect, because the alternative is conceivable and therefore implies no contradiction. 3b. Observation alone cannot establish the law of cause-and- effect, because this is itself an unobserved matter of fact, so the argument would be circular. Therefore, we never have any reason to believe any unobserved matter of fact. Let us now cross-examine these two formal arguments, and see why Hume's assumption about reason (premise#3 in the first argument) is crucial for his second argument to work. Interestingly, it is actually used twice in the second argument - in premises#2 and 3a. Premise #2 claims that we cannot come to know about unobserved matters of fact just by reasoning about them. Why? Because the contrary to every matter of fact is conceivable, conceivable things are not contradictions, and reason does nothing except locate the presence or absence of contradictions. Premise #3a claims that we cannot come to know the law of cause-and- effect just by reasoning about it. Why? Because the contrary of the law of cause-and-effect is conceivable, conceivable things are not contradictions, and reason does nothing except locate the presence or absence of contradictions. So Hume's basic assumption about reasoning is absolutely crucial at both steps. Suppose someone had a different theory of reasoning. Hume's argument would fall apart. A critic could accept everything else that Hume says, but claim that reason does more than merely locate the presence or absence of contradictions. Perhaps we use reason to directly justify our beliefs about unobserved matters of fact. Or perhaps we use reason to justify the law of cause-and-effect (major premise), coupled with our knowledge of observed matters of fact (minor premise), to justify our beliefs about unobserved matters of fact (conclusion). In either case, Hume's problem of induction dissolves. Only if reason is as weak as Hume says would his skepticism about induction follow. But Hume never proves the weakness of reason. Instead, he accepts the weakness as a basic premise, claiming that no one denies it: "[W]hatever we conceive is possible, at least in a metaphysical sense: but wherever a demonstration takes place, the contrary is impossible, and implies a contradiction. And this is a principle, which is generally allowed by philosophers."7 Since his conclusions differ so radically from those of earlier philosophers, Hume should have considered that they might not accept the same conception of reason. At the very least, he should have argued for his position, instead of just asserting that, "To form a clear idea of any thing, is an undeniable argument for its possibility, and is alone a refutation of any pretended demonstration against it."8 But is it? Only if we accept Hume's view of reason in the first place, according to which reason does nothing except locate the presence or absence of contradictions. How would Hume convince someone who didn't already agree? I don't think that he could. 4. An Alternative Conception of Reason Consider the claim: Circular arguments are invalid. Think about it for a while. You can see that it is true -- but how? Even though Hume himself uses this principle in his argument, we could never justify it on his principles. The denial is not a contradiction. We can at least conceive that "Some circular arguments are valid" is true. But at the same time, this principle is not a mere matter of fact. Once we grasp the principle, we see that it is true always and everywhere; moreover, we grasp it by the mere operation of thought. Or consider the claim: The argument ad hominem is a fallacy. Again, the denial is not a contradiction; yet we grasp that it is universally true with the mere operation of thought. I think that these two claims are convincing counter- arguments to Hume's conception of reason. Reason does more than merely discover the presence of absence of contradictions. Frequently, we justify necessary truths just by thinking about them; and sometimes, the opposite of these necessary truths is still conceivable and hence not a contradiction. What is so amazing about this claim? It just turns out that Hume underestimates the power of reason when he limits it to locating the presence or absence of contradictions. I probably won't convince anyone in so brief a presentation. But at least let me raise some doubts in the minds of convinced Humeans. Hume claims that reason cannot justify the law of cause- and-effect. I think that it plainly does. We grasp that "Circular arguments are invalid" and "The argument ad hominem is false" by the pure operation of thought, even though their opposites are conceivable and hence not contradictions. I say that we justify the claim "Every effect has a cause; the same cause always produces the same effect" in exactly the same manner. Namely, we think about the claim; and if we are sufficiently intelligent, open-minded, and intellectually honest, we immediately see its truth. 5. Conclusion Hume assumes that reasoning can do nothing except locate the presence or absence of contradictions. Moreover, his argument that we never have any reason to believe any unobserved matter of fact crucially depends on this unproven assumption. For if reason could do something more than locate the presence or absence of contradictions, we could use reason to justify our claims about unobserved matters of fact. Reason might directly give us a reason to believe unobserved matters of fact; or, reason might give us a reason to believe the law of cause-and-effect, which coupled with immediate observations would give us a reason to believe unobserved matters of fact. I have not proved that this alternative conception of reason is correct. But we should at least consider it. Not only do the examples in the section four tend to support it; but it is also the most likely escape route from the long list of absurd conclusions Hume's premises imply. No one accepts Hume's conclusions in practice; it is time to question his theory as well. Notes 1: David Hume, An Enquiry Concerning Human Understanding, pp.15-16. 2: ibid, p.22. 3: David Hume, A Treatise of Human Nature, pp.86-87. 4: ibid, p.89. 5: David Hume, Abstract of a Treatise of Human Nature, pp.13- 14. 6: ibid, p.17. 7: ibid, p.14. 8: A Treatise of Human Nature, op. cit., p.89.