The contradictory of determinism; that is, the theory that at least some events have no cause.

An alternative formulation is that some event could, or might, have been different even if everything in the universe up to the time of its occurrence had been the same. (Here there are problems about the interpretation of ‘could’ and ‘might’.)

Indeterminism has been claimed mainly for quantum events in physics and for human acts of free will, where incompatibilists (see: compatibilism) think it indispensable.

Attempts have been made to use the indeterminism of quantum phenomena to ground that of human actions, but objections have been raised that more is needed if actions are to be more than random occurrences.

Also see: libertarianism

G E M Anscombe, ‘Causality and Determination’, reprinted in E Sosa, ed., Causation and Conditionals (1975))

Necessary but insufficient causation

Indeterminists do not have to deny that causes exist. Instead, they can maintain that the only causes that exist are of a type that do not constrain the future to a single course; for instance, they can maintain that only necessary and not sufficient causes exist. The necessary/sufficient distinction works as follows:

If x is a necessary cause of y; then the presence of y implies that x definitely preceded it. The presence of x, however, does not imply that y will occur.

If x is a sufficient cause of y, then the presence of y implies that x may have preceded it. (However, another cause z may alternatively cause y. Thus the presence of y does not imply the presence of x, or z, or any other suspect.)

It is possible for everything to have a necessary cause, even while indeterminism holds and the future is open, because a necessary condition does not lead to a single inevitable effect. Indeterministic (or probabilistic) causation is a proposed possibility, such that “everything has a cause” is not a clear statement of determinism.

Probabilistic causation

Interpreting causation as a deterministic relation means that if A causes B, then A must always be followed by B. In this sense, war does not cause deaths, nor does smoking cause cancer. As a result, many turn to a notion of probabilistic causation. Informally, A probabilistically causes B if A’s occurrence increases the probability of B. This is sometimes interpreted to reflect the imperfect knowledge of a deterministic system but other times interpreted to mean that the causal system under study has an inherently indeterministic nature. (Propensity probability is an analogous idea, according to which probabilities have an objective existence and are not just limitations in a subject’s knowledge).[2]

It can be proved that realizations of any probability distribution other than the uniform one are mathematically equal to applying a (deterministic) function (namely, an inverse distribution function) on a random variable following the latter (i.e. an “absolutely random” one[3]); the probabilities are contained in the deterministic element. A simple form of demonstrating it would be shooting randomly within a square and then (deterministically) interpreting a relatively large subsquare as the more probable outcome.

Intrinsic indeterminism versus unpredictability

A distinction is generally made between indeterminism and the mere inability to measure the variables (limits of precision). This is especially the case for physical indeterminism (as proposed by various interpretations of quantum mechanics). Yet some philosophers have argued that indeterminism and unpredictability are synonymous.[4]


One of the important philosophical implications of determinism is that, according to incompatibilists, it undermines many versions of free will, also undermining the sense of moral responsibility and the judgement of regret. You wouldn’t even pass the judgement of regret since moral responsibility is irrelevant; murdering a man would be no different than drinking water when you are thirsty. First of all, this lack of moral responsibility is chaotic in and of itself; the act of drinking water is certainly morally distinct from murdering a man. To clarify, a deterministic world would consider your action, such as murdering a man, to be the only possibility of what could have happened; the outcome of not murdering the man is literally impossible. If this was true, as Kant states, if our will is determined by antecedent causes, then we are no longer the ones responsible for those actions, because those actions that are determined by a force outside of ourselves. The moral reality of our world is greatly disturbed by determinism, because murdering a man is clearly morally wrong.

The judgement of regret is also irrelevant in a deterministic world according to William James in his “Dilemma of Determinism”. We simply would have no logical reason to regret, to consider an “impossible” event to happen in place of “necessity”, to make moral judgements on past events that could not possibly obtain any other outcome. Our ability and will to pass the judgement of regret, on the contrary, is proof that our world is in fact indeterministic and reaffirms the uncertainty of the outcomes of events. The judgement of regret can be effectively passed, because our will is not determined by antecedent causes. Bertrand Russell presents an argument in his essay “Elements of Ethics” against these antecedent causes. Imagine this, we are presented with two alternative choices; determinism maintains that our will to choose one of them is driven by an antecedent cause, and the other two alternatives would be impossible, “but that does not prevent our will from being itself the cause of the other effects (Russell).” The fact that different possibilities are able to be caused and chosen by our will means that morality (right and wrong) is able to be distinguished from the choices. The ability to effectively judge the different possible outcomes is rock hard proof that moral responsibility exists and should be kept in check, and it lines up perfectly with indeterminism.

6 thoughts on “Indeterminism

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