What Is Incompatibilism? The View That Freedom and Determinism Cannot Coexist

Direct Answer

Incompatibilism is the philosophical thesis that free will and causal determinism are logically incompatible: if determinism is true, no one has free will, and if anyone has free will, determinism is false. The incompatibilist insists that the two claims cannot be squeezed together — a free choice must be a genuinely open choice, and a determined choice is never genuinely open.

Incompatibilism is a family of positions rather than a single doctrine. Hard determinists accept determinism and conclude that free will does not exist. Libertarians accept that we are free and conclude that determinism is false. Hard incompatibilists argue that free will fails either way, whether or not determinism is true. What unites them is the rejection of compatibilism, the view that freedom and determinism can coexist.

Historical Context

The intuition behind incompatibilism is ancient. It appears whenever philosophers insist that genuine freedom requires "the power of contrary choice" — the ability to have done otherwise — because that power is exactly what determinism denies. In the medieval period, the dispute over divine foreknowledge was effectively a dispute over incompatibilism: if God already knows what you will do, can your choice be free? Augustine and Aquinas labored to show it could; their critics doubted it.

In the early modern period, Spinoza drew the hard-determinist conclusion with uncompromising clarity: universal necessity leaves no room for freedom, and the belief in freedom is ignorance of causes. Schopenhauer sharpened the point: character is fixed, motives are fixed, and the will is their slave. Against this lineage, libertarians from Kant to William James insisted that morality requires freedom and that the world must therefore leave room for it. The twentieth-century formulation of the debate owes its rigor to Peter van Inwagen's An Essay on Free Will, which gave incompatibilism its most precise modern argument.

Key Concepts

The consequence argument. If determinism is true, our actions are the consequences of the remote past together with the laws of nature. Neither the past nor the laws are up to us. Therefore our actions are not up to us. Since freedom requires that our actions be up to us, determinism rules out free will.

The principle of alternate possibilities. The claim that an agent is morally responsible for an action only if she could have done otherwise. If determinism eliminates alternate possibilities, it eliminates responsibility as well — this is the link between incompatibilism and ethics.

Hard determinism. Accepts determinism, rejects free will. Associated with Holbach, Spinoza, and modern skeptics such as Derk Pereboom.

Libertarianism. Accepts free will, rejects determinism. Modern versions include event-causal libertarianism (Robert Kane) and agent-causal libertarianism (Roderick Chisholm).

Hard incompatibilism. The claim that free will is impossible whether the world is deterministic or not: chance cannot ground authorship any better than necessity can.

Philosophical Perspectives

Hard determinists regard the consequence argument as decisive. Given determinism, your present action was fixed by events long before you were born; you are the vehicle of causes, not their origin. The experience of deliberation is real, but its outcome was settled in advance. On this view, the appropriate response is to reshape moral and legal practice so that it no longer depends on basic desert — a position developed by Pereboom and Gregg Caruso, who argue that punishment should aim at prevention and rehabilitation, not retribution.

Libertarians reply that determinism is not the only option. If quantum mechanics introduces genuine indeterminacy into the physical world, then not every event has a unique possible outcome. Robert Kane's event-causal libertarianism locates free will in "self-forming actions": moments of inner conflict in which the agent's effort makes one of several open possibilities actual. Agent-causal libertarians, following Thomas Reid and Roderick Chisholm, go further: the agent herself is the cause of her free actions, an origin of causality not reducible to prior events.

Hard incompatibilists press the question libertarians avoid: how does adding a little randomness help? If the outcome of your deliberation is undetermined, then whether you choose A or B may be a matter of chance — and chance is not authorship. Pereboom's argument concludes that free will and basic desert responsibility are illusions on either branch of the alternative. This has made hard incompatibilism the sharpest contemporary challenge to both camps.

Modern Reflection

Incompatibilism today is defended less through theology and more through cognitive science. The finding that decisions can be predicted from brain activity before conscious awareness is often read as evidence that the "choice" was fixed before the agent knew about it — a neuroscientific version of the consequence argument. Compatibilists object that prediction is not determination, but incompatibilists respond that the data at least shift the burden of proof onto the compatibilist.

The stakes are institutional. Incompatibilist skeptics argue that the criminal justice system should abandon retributive punishment because no one deserves blame in the basic desert sense. Libertarian incompatibilists reply that abandoning responsibility would be catastrophic and that the openness of human decision-making is real. The free will debate thus remains what it has always been: a contest over whether the universe leaves room for agency, with everything from punishment to self-respect hanging in the balance.

Related Thinkers

• Arthur Schopenhauer — character and motives fix the will
• Kant — freedom as a postulate required by morality
• William James — "The Dilemma of Determinism"
• Daniel Dennett — the compatibilist opponent of incompatibilism

Related Quotes

• "Man is a slave to his character; he can do what he wills, but he cannot will what he wills." — Arthur Schopenhauer
• "If determinism is true, our actions are not up to us, for they are consequences of the past and the laws." — paraphrase of Peter van Inwagen, An Essay on Free Will
• "The dilemma of determinism is not a scientific question but a moral one." — William James

Sources

• Arguments for Incompatibilism — Stanford Encyclopedia of Philosophy
• Incompatibilism (Theories) — Stanford Encyclopedia of Philosophy
• Compatibilism — Stanford Encyclopedia of Philosophy
• An Essay on Free Will — Peter van Inwagen, Oxford University Press

Further Learning

• Continue with What Is Compatibilism?, What Is Free Will?, and What Is Determinism?
• Study the Free Will topic and the Understanding Reality collection
• Read about metaphysics and the philosophy of action