What Is Indeterminism as a Philosophical Doctrine

Indeterminism is the doctrine that not every event is causally determined: some events occur without a sufficient prior cause, leaving more than one future genuinely open. Where the determinist holds that the state of the world at any time, together with the laws of nature, fixes the state at all later times, the indeterminist holds that at least some transitions are not fixed — that chance, randomness, or genuine possibility enters the world. The doctrine has two faces. As a thesis in the philosophy of science, it is the claim that the fundamental physics of the world is not deterministic — a claim given dramatic support by quantum mechanics. As a thesis in the free will debate, it is the claim that the incompleteness of causation is the condition of freedom: that we are free because our choices are not necessitated.

Indeterminism is the natural ally of libertarianism, the view that free will exists and is incompatible with determinism. But the alliance is uneasy. The libertarian needs more than indeterminism: an action that is merely uncaused, or caused by pure chance, is not obviously free — indeed, randomness seems as hostile to responsibility as necessity. The problem of showing how chance can ground freedom, rather than undermine it, is the deepest difficulty for indeterminist theories of free will. William James embraced the difficulty head-on, defending "the chance" as the only basis for a world in which effort and moral life are real.

Historical Background

The history of indeterminism runs parallel to the history of determinism. The ancient atomists were determinists; Epicurus introduced the famous "swerve" (clinamen) — a spontaneous deviation in the motion of atoms — precisely to break the chain of necessity and leave room for freedom. The doctrine was revived whenever the philosophical or scientific orthodoxy became too deterministic. William James, in his essay "The Dilemma of Determinism" (1884), argued that determinism makes the distinction between good and evil ultimately meaningless, because everything that happens happens necessarily: "The stronghold of the determinist argument is the antipathy to the idea of chance." James embraced chance as the only alternative to a world in which regret and effort are illusions.

The twentieth century gave indeterminism its scientific charter. Quantum mechanics, in its standard interpretation, is irreducibly indeterministic: the outcomes of measurements at the quantum level are not fixed by prior states but are genuinely random, describable only probabilistically. The discovery transformed the terms of the debate. Where Laplace's demon had made determinism seem like the inevitable scientific worldview, quantum mechanics suggested that nature itself contains real chance. Whether this helps the free will debate, however, is contested: Dennett and others have argued that quantum randomness is no more a basis for freedom than determinism is — a choice caused by random noise is as involuntary as a choice caused by a deterministic chain.

Key Arguments

The Argument from Quantum Mechanics

The empirical argument for indeterminism appeals to the state of fundamental physics. According to the standard (Copenhagen) interpretation of quantum mechanics, the state of a quantum system evolves deterministically until a measurement occurs, at which point the outcome is not determined by the prior state — only its probability is. If nature is fundamentally indeterministic in this way, then the universe is not the Laplacean machine the determinist describes. The argument has limits, however. There are deterministic interpretations of quantum mechanics (notably the de Broglie-Bohm pilot-wave theory), the indeterminacy may be confined to the microscopic domain, and even if nature is indeterministic, the relation between quantum events and human decisions is entirely unclear.

The Argument from the Experience of Freedom

The experiential argument, classically stated by William James, begins from the felt openness of the future. When we deliberate, we experience the alternatives as genuinely open: it is up to us which option we take, and we feel that the outcome is not settled in advance. The determinist must dismiss this experience as an illusion; the indeterminist can take it at face value. James argued that the "judgment of regret" — the conviction that some past choice was genuinely bad and could have been avoided — is indispensable to moral life and impossible on the determinist picture. The argument is powerful but not decisive: the compatibilist replies that the experience of openness is compatible with causation, since what we experience is the absence of constraint, not the absence of causes.

The Argument from Chance to Freedom: The Problem

The libertarian's constructive argument faces the famous "problem of chance": if an action is not determined, its occurrence is a matter of randomness — and a random action is not one for which the agent is responsible. The problem can be stated as a dilemma: either the choice is determined by the agent's character and reasons (in which case it is determined, and the libertarian has conceded compatibilism), or it is not (in which case it is random, and the agent is not responsible for it). Libertarian theories respond by locating indeterminacy not in the act but in the process of deliberation: the agent's reasons, character, and effort are what determine the outcome, but they do not determine it inevitably — the weighing of reasons is an irreducibly agential activity. Robert Kane's "ultimate responsibility" theory is the most developed version of this response: free choices are those for which the agent is ultimately responsible, in virtue of earlier "self-forming actions" that were themselves undetermined.

Contemporary Relevance

Indeterminism remains a live position in the free will debate, though it is a minority one. The scientific question — is the world deterministic? — is now empirical, and the answer is unsettled: quantum mechanics is indeterministic on its standard interpretation, but deterministic alternatives remain viable, and the question of whether any indeterminacy reaches the level of human decision-making is open. The philosophical question — could indeterminism ground freedom even if it were true? — is the deeper one, and it divides libertarians themselves. Meanwhile, the cognitive sciences have added a new wrinkle: if our decisions are influenced by random noise in the brain (as some studies suggest), the result is not freedom but a new form of non-control. The debate between determinism, compatibilism, and indeterminism is thus as much about the concept of freedom as about the facts of physics.

Sources

• Stanford Encyclopedia of Philosophy, "Causal Determinism"
• Stanford Encyclopedia of Philosophy, "Free Will"
• Stanford Encyclopedia of Philosophy, "William James"
• Internet Encyclopedia of Philosophy, "Indeterminism and Free Will"

Related Topics

• What is determinism? — the thesis indeterminism denies
• Determinism — the opposing doctrine
• Compatibilism — the view that freedom needs no indeterminism
• Free will — the concept at stake in the debate
• Chance and freedom — the scientific context of the debate
• Causality — the relation whose completeness is in question