Laplace imagined a mind that could read the entire future from particle positions
Picture an observer who knows the exact position and velocity of every particle in the universe. Pierre-Simon Laplace argued such a being could calculate everything still to come. His imaginary demon became the emblem of determinism, the view that events can unfold in only one possible way.
Determinism comes in many flavours. Causal determinism says each event is necessitated by earlier conditions plus the laws of nature; its most common form, nomological or physical determinism, holds that past and present fix the future completely. Necessitarianism goes further and denies there is any other possible world at all, an idea with ancient roots: Leucippus held that nothing happens without a cause and everything happens by necessity. Predeterminism adds that the chain was set up in advance, stretching back to the origin of the universe.
Religious versions split into strong and weak forms. The strong form says an all-powerful deity scripted every event; the weak form rests only on divine foreknowledge, since whatever a perfectly knowing God foresees must come to pass. Some claim Augustine of Hippo brought theological determinism into Christianity in 412 CE, after earlier Christian writers had defended free will against Stoic and Gnostic determinism. Fatalism is usually kept separate, because fate need not follow causal laws at all.
Physics complicates the picture. Stephen Hawking described quantum mechanics as governed by laws that fix the probabilities of different futures rather than a single future. Adequate determinism replies that quantum randomness averages out across huge numbers of particles, so everyday objects behave classically, with rare exceptions such as a Geiger counter's clicks. The many-worlds interpretation suggests every outcome occurs in branching parallel states, which could keep the whole globally deterministic.
Other theories target human behaviour. Biological or genetic determinism says genes fix our beliefs and desires; John B. Watson and B. F. Skinner developed behaviourism, a nurture-focused counterpart, and cultural determinism credits upbringing. The strongest single-factor versions are now widely rejected as a single-cause fallacy. Philosophers remain divided on free will: compatibilists think it can coexist with a determined world, while incompatibilists deny this.
Source: Determinism
