Practical Reason: Instrumentalism and Nihilism
Most of us think that some behavior is more reasonable than others. There seems to be something unreasonable about, say, eating aluminum foil. But Hume denied that reason has any important role in motivating or discouraging behavior. After all, reason is just a sort of calculator of concepts and experience. What ultimately matters, Hume said, is how we feel about the behavior. His work begot the doctrine of instrumentalism, which states that an action is reasonable if and only if it serves the agent's goals and desires, whatever they be. Reason can enter the picture only as a lackey, informing the agent of useful facts concerning which actions will serve his goals and desires, but never deigning to tell the agent which goals and desires he should have. So, if you want to eat aluminum foil, reason will tell you where to find the stuff, and there's nothing unreasonable about eating it or even wanting to do so. Instrumentalism went on to become the orthodox view of practical reason in economics, rational choice theory, and some other social sciences. But, some commentators argue, Hume actually went a step further to nihilism and said there's nothing unreasonable about deliberately frustrating your own goals and desires ("I want to eat aluminum foil, so let me wire my mouth shut"). Such behavior would surely be highly irregular, granting reason no role at all, but it would not be contrary to reason, which is impotent to make judgments in this domain.
For relevant contemporary work, see Jean Hampton's The Authority of Reason and David Schmidtz's Rational Choice and Moral Agency.
Moral Anti-Realism and Motivation
Drawing on his attack on reason's role in judging behavior, Hume argued that immoral behavior is not immoral by being against reason. He first claims that moral beliefs are intrinsically motivating—if you believe killing is wrong, you will be ipso facto motivated not to kill and to criticize killing and so on (moral internalism). He then reminds us that reason alone can motivate nothing—reason discovers matters of fact and logic, and it depends on our desires and preferences whether apprehension of those truths will motivate us. Consequently, reason alone cannot yield moral beliefs. Hume proposed that morality ultimately rests upon sentiment, with reason only paving the way for our sensitive judgments by analysis of the moral matter in question. This argument against founding morality on reason is now one in the stable of moral anti-realist arguments; Humean philosopher John Mackie argued that, for moral facts to be real facts about the world and, at the same time, instrinsically motivating, they would have to be very weird facts. So we have every reason to disbelieve in them.
For relevant contemporary work, see J. L. Mackie's Ethics: Inventing Right and Wrong, Mackie's Hume's Moral Theory, David Brink's Moral Realism and the Foundation of Ethics, and Michael Smith's The Moral Problem.
Free Will vs. Indeterminism
Just about everyone has noticed the apparent conflict between free will and determinism—if your actions were determined to happen billions of years ago, then how can they be up to you? But Hume noted another conflict, one that turned the problem of free will into a full-fledged dilemma: free will is incompatible with indeterminism. Imagine that your actions are not determined by what events came before. Then your actions are, it seems, completely random. Moreover, and most importantly for Hume, they are not determined by your character—your desires, your preferences, your values, etc. How can we hold someone responsible for an action that did not result from his character? How can we hold someone responsible for an action that randomly occurred? Free will seems to require determinism, because otherwise, the agent and the action wouldn't be connected in the way required of freely chosen actions. So now, nearly everyone believes in free will, free will seems inconsistent with determinism, and free will seems to require determinism. Hume's view is that human behavior, like everything else, is caused, and therefore holding people responsible for their actions should focus on rewarding them or punishing them in such a way that they will try to do what is morally desirable and will try to avoid doing what is morally reprehensible. (See also Compatibilism.) How can we resolve this dilemma?
The Is-Ought Problem
Hume noted that many writers talk about what ought to be on the basis of statements about what is. But there seems to be a big difference between descriptive statements (what is) and prescriptive statements (what ought to be). Hume calls for writers to be on their guard against changing the subject like that, not without giving an explanation of how the ought-statements are supposed to follow from the is-statements. But how exactly can you derive an 'ought' from an 'is'? That question, prompted by Hume's small paragraph, has become one of the central questions of ethical theory, and Hume is usually assigned the position that such a derivation is impossible. Others interpret Hume as saying not that one cannot go from a factual statement to an ethical statement, but that one cannot do so without going through human nature, that is, without paying attention to human sentiments. The "imposssible" view was assumed by G. E. Moore's "open question argument", intended to refute any identification of moral properties with natural properties—the so-called "naturalistic fallacy". Now any ethical theorists who wish to give morality an objective grounding in more down-to-earth features of the world is fighting an uphill battle, especially if they seek to do that without taking account of the role of human sentiments and empathy in the formulating of moral judgements.
Hume, along with his fellow members of the Scottish Enlightenment, first advanced the idea that moral rules are justified by promoting the utility of the persons involved. Hume's role is not to be overstated, of course; it was his countryman Francis Hutcheson who coined the utilitarian slogan "greatest happiness for the greatest numbers". But it was from reading Hume's Treatise that Jeremy Bentham first felt the force of a utilitarian system: he "felt as if scales had fallen from [his] eyes". But Hume's proto-utilitarianism is a peculiar one from our perspective. He doesn't think that the aggregation of cardinal units of utility provides a formula for arriving at moral truth. On the contrary, Hume thinks that moral principles aren't intellectually justifiable—some rules appeal to us and others don't. But, he thinks, the reason that good moral principles appeal to us is that they promote our interests and those of our fellows, with whom we sympathize. Humans are hard-wired to approve of things that help society—public utility. Hume used this insight to morally appraise things from social institutions and government policies to character traits and talents. The legacy of utilitarianism is too well-known to go into—the theory is a mainstay of ethics and economics.
The Problem of Miracles
One way to support a religion is by appeal to miracles. But Hume argued that, at minimum, miracles could never give religion much support. There are several arguments suggested by Hume's essay, all of which turn on his conception of a miracle: namely, a violation of the laws of nature by God. One argument claims that it's impossible to violate the laws of nature. Another claims that human testimony could never be reliable enough to countermand the evidence we have for the laws of nature. The weakest and most defensible claims that, due to the strong evidence we have for the laws of nature, any miracle claim is in trouble from the get-go, and needs strong supporting evidence to defeat our initial presumptions. In a slogan, extraordinary claims require extraordinary evidence. This point has been most applied to the question of the resurrection of Jesus, where Hume would no doubt ask, "Which is more likely—that a man rose from the dead or that this testimony is mistaken in some way?" Or, more blandly, "Which is more likely—that Uri Geller can really bend spoons with his mind or that there is some trick going on?" This argument is the backbone of the skeptic's movement and a live issue for historians of religion. For a critical and technical (Bayesian) analysis of Hume, see John Earman's Hume's Abject Failure—the title of which gives you an idea of his assessment.
The Design Argument
One of the oldest and most popular arguments for the existence of God is the design argument—that all the order and 'purpose' in the world bespeaks a divine origin. Hume gave the classic criticism of the design argument, and though the issue is far from dead, many are convinced that Hume killed the argument for good. All a century before Darwin! Here are some of his points:
For relevant contemporary work, see J. C. A. Gaskin's Hume's Philosophy of Religion, and Richard Swinburne's The Existence of God; for a view from a philosopher of
- For the design argument to work, it needs to be true that about the only time we see order and perceived purpose is when it results from design. But we see the stuff all the time, resulting from presumably mindless processes like generation and vegetation. Design accounts for only a tiny part of our experience with order and 'purpose'.
- The design argument, even if it worked, could not support a robust theism; all you can hope for is the conclusion that the universe's configuration is the result of some morally ambiguous, possibly unintelligent agent or agents whose method bears some remote similarity to human design.
- By the design argument's own principles, God's mental order and functionality needs explanation. Otherwise, we could leave the universe's order, etc. unexplained.
- Often, what appears to be purpose, where it looks like object X has feature F in order to secure some outcome O, is better explained by a filtering process: that is, object X wouldn't be around did it not possess feature F, and outcome O is only interesting to us, a human projection of goals onto nature. This mechanical explanation of teleology anticipated natural selection.