7.3 Hume on Liberty and Necessity

What this lecture covers

This lecture turns from Hume's definition of liberty to what Millican calls his most distinctive contribution to the free will debate: an argument for determinism itself, drawn from Hume's account of causation in Inquiry Section 7 and applied to human action in Section 8. It builds on the previous lecture's distinction between intentional agency and unwelcome restriction as separate concepts of freedom.

You'll come away able to state Hume's constant-conjunction theory of causation, explain how he applies it to argue that human action is just as determined as physical events, and see why he thinks this actually supports, rather than undermines, moral responsibility.

Key ideas

• Hume's theory of causation: our idea of necessary connection comes entirely from observing constant conjunctions of similar events and the resulting habit of inferring one from the other, not from perceiving any intrinsic necessity.
• Applying this to the mind: if constant conjunction and inference are what causation ultimately consists in, and the same patterns show up in human behavior, then there is just as much reason to call human action determined as to call physical events determined.
• Predictability of human action: Hume argues everyday life presupposes that people are predictable, illustrated by a condemned prisoner reasoning about both physical obstacles and how his jailers will behave.
• Why people deny determinism despite acting on it: Hume claims people mistakenly believe they grasp a deeper necessity in physical causes, like colliding billiard balls, than in human motives, when in fact neither is intuitively comprehensible.
• Determinism supports morality, on Hume's view: an action is only mine, and only something I can be praised or blamed for, if it arises from my enduring character, desires and reasoning; a genuinely random action would be harder, not easier, to hold me responsible for.

Walkthrough

Hume's account of causation (0:11)

The lecture recaps Hume's claim from Inquiry Section 7 that our idea of causal necessity comes purely from observing constant conjunctions, such as one billiard ball's motion regularly followed by another's, and from the habitual inference this produces, not from perceiving any real connection between cause and effect.

Extending causation to human action (2:13)

Hume argues that if constant conjunction and inference are all that causal necessity ever amounts to, and these patterns are found in human behavior just as much as in physical events, then human action is determined in exactly the sense that physical events are. The prisoner-awaiting-execution example shows how naturally we combine physical and behavioral predictions in everyday reasoning.

Why people resist the conclusion (6:15)

Hume suggests people deny determinism about their own actions because they wrongly believe they intuitively understand physical causation, as with colliding billiard balls, in a way they do not understand human motives. The lecture notes this anticipates modern physics, where even basic physical processes turn out not to be intuitively comprehensible either.

Determinism as the foundation of moral responsibility (8:19)

Rather than undermining moral responsibility, Hume argues determinism is required for it: an action is attributable to me, and so open to praise or blame, only if it flows from my intentions, desires and settled character. An action that occurred at random, unconnected to my character, would be harder to hold me responsible for, not easier.

Before you watch

• Watch "7.2 Different Concepts of Freedom" first, since this lecture continues its discussion of Hume's minimal notion of liberty.
• Familiarity with Hume's discussion of induction and causation from earlier in the course is directly relevant here.

Check your understanding

1. According to Hume, what does our idea of necessary connection actually derive from?
2. How does Hume use the prisoner example to argue that human action is as predictable as physical events?
3. Why does Hume think people wrongly believe physical causation is more intelligible than human motivation?
4. Explain Hume's argument that determinism supports, rather than undermines, moral responsibility.