Determinism is the philosophical view that past events and the laws of nature fix or set future events. The interest of determinism in analytic 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 of 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.
There are two major varieties of determinism. First is, Causal determinism which 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. Secondly is, Correlative determinism which 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.
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.
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 operates under the following conditions,
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.
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.
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 (Bohm 1952). Hidden-variable theories merely posit variables that are inaccessible to physicists experimentally, but that, nevertheless, allow physicists to describe a physical state deterministically.
Therefore, the problem with basing an argument for causal indeterminism on quantum physics is that quantum theory can be interpreted deterministically. The philosophical explanation for this predicament is that any physical theory is underdetermined by the evidence that supports it, which is known as the Quine-Duhem thesis in the philosophy of science (Duhem  1954; Quine 1951).
The Quine-Duhem thesis states that any physical phenomena can be explained by more than one physical theory (or theoretical interpretation) since all physical theories need background assumptions to explain physical phenomena, and background assumptions can be manipulated to accommodate several different theories. Thus quantum phenomena that appear indeterministic can be explained as deterministic, albeit in a slightly more complicated way, just by tinkering with background assumptions.
As for philosophical theories of indeterministic causation, these theories have had their problems as well. Namely, theories of probabilistic causation have been charged with basing their theory of causation on a false premise. All probabilistic theories of causation assume that a cause increases the probability of its effect. In Wesley Salmon’s (1993) words, “it seems intuitively compelling to argue that a cause which contributes probabilistically to bringing about a certain effect must at least raise the probability.” Nevertheless, this view of causation is susceptible to a certain sort of counterexample.
Germund Hesslow (1976) provides the classic counterexample. Hesslow points out that taking contraceptive pills or being pregnant can cause thrombosis onset; which is abnormal blood clotting. However, since taking contraceptive pills decreases the probability of becoming pregnant, taking contraceptive pills actually decreases the probability of thrombosis onset. Hence we have an example of a cause (taking contraceptive pills) decreasing the probability of its effect (thrombosis onset). Thus there are philosophical challenges to making theories of indeterministic causation plausible in the first place.
Despite this criticism, philosophers, such as Wesley Salmon (1984), evade the criticism by opting to represent causation as a process instead of a relation between events. Salmon's process theory of probabilistic causation not only evades Hesslow's criticism, but explains how causal indeterminism is possible.
Determinism is regularly used in metaphysical debates over the existence of free will, which is roughly the power to choose one’s actions. Hard determinists believe that not only is determinism true, but its truth precludes the existence of free will. Soft determinists (or compatibalists) believe that while determinism is true, it does not preclude the existence of free will. Also, libertarians are those who believe that free will exists exactly because determinism is not true.
Disagreements among philosophers over the existence of free will correlate with the philosophical view one holds about determinism. For example, Peter van Inwagen (1983), who argues against soft determinism, interprets determinism as a view about the relation between the world’s events (event causation). However, Roderick Chisholm (1964), who argues in favor of soft determinism, interprets determinism as a view about the relation between world events and agents (agent causation). Furthermore, Robert Kane (1999), a noted libertarian, rejects determinism altogether.
Nevertheless, some philosophers, such as Immanuel Kant ( 1993), see the debate over free will as a debate over the definition of ‘free will’ instead of the truth or nature of determinism. Still other philosophers, such as Harry Frankfurt (1969), argue that the free will debate is not all that important in the first place, since what we care most about in the debate is moral responsibility, and the existence of moral responsibility does not depend on whether we have free will. Nevertheless, the truth and nature of determinism is overwhelmingly seen to have some bearing on whether free will exists, and, furthermore, the topic of determinism will continue to be discussed in philosophy as a topic in its own right.
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