The problem of moral motivation asks what connection holds between moral judgment and motivation to act. Motivational internalism holds that there is a necessary connection: genuinely judging that an action is right entails being at least somewhat motivated to do it. If someone sincerely says "I know I ought to help, but I have absolutely no motivation to do so," the internalist concludes that the person does not genuinely hold that moral judgment. Motivational externalism denies this necessary connection, allowing that moral judgments are beliefs about moral facts that may or may not motivate depending on the agent's desires. The Humean theory of motivation, which holds that only desires (not beliefs alone) can motivate action, supports externalism: if moral judgments are beliefs, they need a separate desire to generate motivation. Anti-Humeans (Nagel, Dancy) argue that beliefs about reasons can motivate directly. This debate intersects with metaethics because non-cognitivists (expressivists) can easily explain moral motivation—moral judgments just are motivational states—while cognitivists face the challenge of explaining why moral beliefs motivate.
Read Michael Smith's The Moral Problem (chapters 1-5) for a clear statement of the tension between internalism, cognitivism, and the Humean theory of motivation. Then consider the case of the amoralist—someone who makes moral judgments but is entirely unmoved—and ask whether such a person is conceptually possible or merely hypothetical.
From your study of moral psychology, you know that moral agents come equipped with both beliefs and desires, and that these interact to produce action. The problem of moral motivation presses on exactly that interaction: when a person forms a moral judgment — "I ought to donate to famine relief" — does that judgment automatically carry some motivational pull, or is it simply a belief that sits inert until paired with the right desire? This question is the pivot between motivational internalism and motivational externalism.
The internalist holds that the connection is necessary. If you genuinely judge that you should act, you are, at minimum, somewhat moved to act. The test case is the so-called amoralist: someone who sincerely says, "Yes, torturing the innocent is wrong, and I feel not the slightest inclination to avoid it." The internalist's response is that this person cannot be sincere — their complete motivational indifference is evidence that they do not actually hold the judgment. They may be saying the words, but something other than a genuine moral judgment is operating. Externalists push back: why couldn't a moral judgment be a belief that the agent simply doesn't care about? After all, a historian might believe that the Roman Empire fell in 476 CE with zero motivational consequence.
The Humean theory of motivation — which you encountered in moral psychology as a foundational claim about action — provides the theoretical backdrop. Hume argued that belief alone can never move us; only desire, or desire-like states (what philosophers sometimes call "pro-attitudes"), can generate motivation. A belief simply reports how things are; it takes a desire to push us toward action. If this is right, and if moral judgments are beliefs (as cognitivists in metaethics hold), then moral judgments require a separate desire to motivate. Externalism then seems forced on us: the connection between judging and acting is contingent, not necessary. Anti-Humeans like Thomas Nagel and Jonathan Dancy resist this picture, arguing that recognizing a reason can itself be motivating — that there are "agent-neutral" reasons that rational beings are moved by through belief alone, without needing a prior desire.
The deepest stakes emerge when you connect this debate to metaethics. Non-cognitivists — especially expressivists — sidestep the internalism puzzle elegantly: if moral judgments are not beliefs at all but expressions of approval, condemnation, or commitment, then of course they motivate. A genuine expression of "I condemn this" is a motivational state by its very nature. But cognitivists — those who think moral judgments are truth-apt beliefs — must explain how beliefs about moral facts get their motivational grip. Michael Smith's classic formulation frames this as a tension among three claims: (1) moral judgments are beliefs (cognitivism), (2) they are necessarily motivating (internalism), and (3) only desires motivate (Humeanism). All three cannot be true together. The problem of moral motivation is the project of deciding which one to give up.
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