You decide to have tea instead of coffee. It feels as though you could have chosen otherwise. But your choice also had causes: your tastes, your mood, your brain chemistry, the events that shaped them. If those causes fixed the outcome, was the choice free? This is the classic problem of free will.

Determinism

Determinism is the thesis that every event, including every human choice, is fixed by prior causes and the laws of nature. In 1814 the French mathematician Pierre-Simon Laplace imagined an intellect that knew every force and the position of every particle; for such a mind, “nothing would be uncertain and the future, as the past, would be present to its eyes.”

Modern physics complicates the picture, since some interpretations of quantum mechanics are indeterministic. But many philosophers think this does not help free will much, because a choice that happens by chance is not more under our control than one that was caused. Free will, as philosophers use the term, means the kind of control over our actions that moral responsibility requires.

Three main positions

• Hard determinism holds that determinism is true and rules out free will. Writers such as the Baron d'Holbach in the eighteenth century argued that humans are part of nature's causal order and that the feeling of freedom is ignorance of our causes.
• Libertarianism (unrelated to the political philosophy of the same name) holds that we have free will, and it requires that determinism be false, at least for some choices. Some libertarians, following Thomas Reid, say agents themselves cause their choices rather than being pushed by prior events. The main objection is that if nothing determines a choice, it is hard to see how it is not simply luck.
• Compatibilism holds that free will and determinism can both be true.

Hume's compatibilism

David Hume, in his Enquiry Concerning Human Understanding (1748), argued that the long dispute was largely verbal. By liberty, he said, we mean only “a power of acting or not acting, according to the determinations of the will.” For Hume, the opposite of liberty is constraint, not causation. A prisoner in chains is unfree; a person choosing breakfast according to their own wishes is free, even if those wishes have causes. Surveys of professional philosophers have found a majority leaning toward some form of compatibilism.

The consequence argument

Incompatibilists reply with what Peter van Inwagen called the consequence argument. In paraphrase: if determinism is true, our acts are consequences of the laws of nature and events in the remote past. We have no control over either. So, it seems, we have no control over their consequences, including our acts.

Frankfurt cases

Many people assume free will requires the ability to do otherwise. In 1969 Harry Frankfurt challenged this with a now famous kind of case. Black wants Jones to perform some act and has secretly fitted a device that will make Jones decide to do it if Jones shows signs of deciding otherwise. As it happens, Jones decides to do the act entirely on his own, and the device never activates. Jones could not have done otherwise, yet he seems fully responsible. A Frankfurt case is designed to show that someone can be responsible even if they could not have done otherwise; what matters is how the action actually came about.

In a later paper (1971), Frankfurt proposed that freedom of the will involves our higher-order attitudes toward our own desires. His unwilling addict craves a drug but wishes he did not have the desire that moves him; the willing addict endorses it. Only the willing addict acts with a will he identifies with, even though both take the drug.

Worked example: returning the wallet

Nadia finds a wallet with a large amount of cash and an ID. After a moment's hesitation, she returns it to its owner. Was her act free? Let us look at it through each position.

Hard determinist. Nadia's honesty came from her upbringing, her temperament and the state of her brain at that moment. Given those causes and the laws of nature, she could not have done otherwise. Her act was good, but she does not deserve credit in any deep sense.

Libertarian. At the moment of hesitation, Nadia's choice was genuinely open. Nothing in the past fixed whether she would keep the cash or return it, and she herself settled the matter. A critic asks: if nothing fixed the outcome, what made it hers rather than a lucky roll of the dice?

Hume's compatibilist. Nadia acted according to her own will, without constraint. No one forced her or threatened her. That is all liberty means, so her act was free, whether or not it was determined.

Frankfurt. Suppose, unknown to Nadia, a friend was watching and would have pressured her to return the wallet had she started to walk away. She could not, in the end, have kept it. But since she returned it on her own, the friend's presence seems irrelevant to her credit. And Nadia endorses her desire to be honest; she is a willing, not an unwilling, agent of it.

Which description feels right to you? Most people find that their judgment of Nadia does not change much, which is part of why compatibilism appeals to so many philosophers.