Determinism

Determinism

Determinism is the philosophical view that past events along with the laws of nature, fix future events. In Peter van Inwagen’s (1983) words, “Determinism is, intuitively, the thesis that, given the past and the laws of nature, there is only one possible future”. The interest of determinism in academic philosophy primarily lies in whether determinism is an accurate description of how the world’s events proceed. However, determinism is also an important part of the metaphysical debate over the existence free will. Thus, it will be important to discuss the varieties of determinism, the critics of determinism, and the application of the thesis of determinism to the debate over free will.

Varieties of Determinism

There are two major varieties of determinism. Causal determinism claims that past events and the laws of nature uniquely cause future events. In other words, causal determinism posits a relation of deterministic causation between past and future events. Correlative determinism claims that past events and the laws of nature fix, but do not cause, future events. In other words, correlative determinism posits a relation of deterministic correlation between past and future events.

Causal Determinism

The usual example of a causally deterministic theory is Newtonian physics. According to Newtonian physics, all events are deterministically caused from past events and the laws of nature, where the laws of nature are various force and motion laws. For instance, according to Newton’s laws of motion and gravity, if the masses of a planet and its satellite are known along with the satellite’s initial velocity tangent to its orbit, then it is possible to predict the trajectory of the satellite around its orbit at arbitrary future times. In fact, one of the greatest accomplishments of Newtonian physics was being able to explain the periodicity of Halley’s comet.

Causal determinism typically presupposes event causation, which is the commonsense causal relation that holds between events and events (e.g. a baseball hitting a window causes the window to shatter). Even though the thesis of causal determinism between events is fairly straightforward, there is a conceptual problem at its lower limit. Namely, if all events are causally determined by past events, then what determined the first event?

The above problem was known since the days of Aristotle [384-322 B.C.E.], and Aristotle’s solution was to posit an “unmoved mover” (e.g. God). In short, at the beginning of the chain of events in the history of the universe, there must have been an agent that caused that chain to begin, an unmoved mover. But then Aristotle generalizes the ability of a supreme unmoved mover to all agents, creating what is known as agent causation. Thus at the beginning of a chain of events, there must be an agent that caused the occurrence of the first event. Aristotle’s famous phrase is, “A staff moves a stone, and is moved by a hand, which is moved by a man”.

Although it is interesting to debate over whether event or agent causation is the appropriate interpretation of causation in the thesis of causal determinism, a much more important debate among determinists is whether determinism should be viewed as causal in the first place.

Correlative Determinism

Philosophers have long been preoccupied with using the least number of assumptions in defending a position. Peter van Inwagen (1983) is one such minimalist philosopher who claims that determinism can be defended without assuming a causal relation between past and future events. Instead, van Inwagen claims, determinism can be viewed as a thesis about propositions that express information about past and future states of the world.

According to van Inwagen, determinism states that, (1) for all times, there is a proposition that expresses the state of the world at that time, (2) there is a set L constituting the laws of nature that apply to all states of the world, and (3) if a proposition P expresses the state of the world at a certain time, while another proposition Q expresses the state of the world at a successive time, then P and L entail Q. Thus van Inwagen’s notion of determinism leaves out the term ‘cause’ and uses a notion of future-to-past uniqueness. Nevertheless, what van Inwagen’s correlative determinism leaves unexplained is how past events come to uniquely determine future events. In other words, how do these deterministic correlations come about in the first place?

There are at least two answers to this question in the history of philosophy: occasionalism and pre-established harmony. Nicholas Malebranche [1638-1715] invented occasionalism, which is the doctrine that God alone is the cause of all events. Thus God intervenes to make any past event give rise to any future event. Thus past and future events are correlated because God makes it look this way. However, occasionalism was criticized for its less than ideal representation of God and his abilities.

In contrast, Gottfried Leibniz [1646-1716] invented the thesis of pre-established harmony to explain how the world’s events proceed. Once again God is the sole cause of all events, but there is but one intervention by God that determines the course of all future events. The thesis of pre-established harmony is analogous to a situation where someone arranges thousands of dominos in a way that if a certain one is hit, then the rest of them will fall in succession.

Critics of Determinism

Although it is an interesting question as to whether determinism is best understood as a causal thesis, a more important question is whether any version of determinism is true. Indeterminism is the thesis that not all future events are fixed by past events. Indeterminists either adopt a view of causal indeterminism or randomness.

Causal indeterminism claims that past events still cause future events, just not in a deterministic fashion. All causal indeterminists adopt some view of indeterministic causation, such as probabilistic causation. The appeal of causal indeterminism traces to the success of quantum physics, or more accurately, the success of the Copenhagen interpretation of quantum physics. According to the Copenhagen interpretation of quantum physics, it is impossible to predict with certainty all of the future states of a physical system. For example, according to Heisenberg’s relations, it is impossible to predict with certainty the z-axis and x-axis angular spin of an electron at any particular time. Thus the spin states of an electron indeterminately arise from its past spin states.

However, the difficulty of causal indeterminism lies in the difficulty of constructing an unproblematic theory of indeterministic causation as well as ruling out deterministic accounts of quantum mechanical phenomena. Let’s start with the later problem first.

Even though the Copenhagen interpretation of quantum physics has been tremendously successful in explaining quantum phenomena, there are rival deterministic theories that can explain the same phenomena. Such theories are known as hidden-variable theories in the literature, and a prominent hidden-variable theory is Bohmian mechanics.

Bibliography

Van Inwagen, Peter. (1983). An Essay on Free Will. Oxford: Oxford University Press.

Suggested Reading

1. Sosa, Ernest, and Tooley, Michael. (1993). Causation. Oxford: Oxford University Press.
2. Stanford Encyclopedia of Philosophy entry on Causal Determinism
3. Watson, Gary. (2005). Free Will. Oxford: Oxford University Press.