A Crucial Mistake in the Free Will Debate

Transcription

1 A Crucial Mistake in the Free Will Debate Richard Johns Department of Philosophy University of British Columbia January 19, 2005 There are usually considered to be three main views about free will, known as hard determinism, compatibilism (including soft determinism) and libertarianism. Unfortunately, the arguments for these views all rest upon a crucial mistake. In this paper I shall describe the Mistake (as I shall call it) and show why it matters. 1. The Mistake In the debate concerning free will, one frequently encounters the view, or sometimes the unconscious assumption, that random events are uncaused. A hard determinist argues, for example, that if certain human actions lacked determining causal antecedents, then those acts would be random, and hence uncaused. Thus, since those actions arise from nowhere, they cannot be regarded as belonging to the human agent, and so are not actions of the agent. Compatibilists also follow this line of thought, using it to argue that their scaled-down version of freedom is the best that one could hope for. Even the libertarian Richard Taylor disastrously agrees, claiming that an indeterministic person would be an erratic and jerking phantom. This view, that random events are uncaused, is when properly understood not merely false but absurd. Its falsehood is very easily seen when one defines everything clearly. So let us define our terms. 1

2 1. A causal process is what physicists call a physical process. It is a series of events where each event directly causes its immediate successor. In general the events of the process are just time slices of it, where the points of division are quite arbitrary. Some examples of causal processes are light rays, particles, wavefronts, and so on. A famous non-causal process (discussed by Wesley Salmon) is a spot of light moving across a screen. Causal processes are continuous in spacetime, and cannot travel faster than the speed of light. 2. An event C causes E when C brings E about, or makes E happen. C is the source of E s existence, and so is said to produce or generate E. This relation requires than C and E be either contiguous or connected by a causal process from C to E. Causation is partial, when C is merely one of the events that helps to produce E, or total, when C alone causes E. Since causation is transitive, one cannot speak of the total cause of E, but merely of the total cause at some particular time prior to E. A cause is always in the past light cone of its effects. 3. An event C (nomically) determines E when C, together with the dynamical laws of physics, logically necessitates E. (This is equivalent to the standard definitions of Montague, Lewis, etc.) Note that C may be either before E or after E in time, as the laws of physics allow us to infer the occurrence of solar eclipses thousands of years ago, as well as in the future. Before we continue defining terms, we should be clear that causation and determination are quite different relations, for the following reasons. 2

3 (i) Causes always precede their effects, whereas determination has no temporal direction. (ii) In situations where there is a back-up cause, such as in Frankfurt scenarios, the back-up cause is needed to determine the event E in question, but does not help to cause E. (iii) Determination is a logical relation, a kind of entailment (and relatively well understood) whereas causation is a deep mystery, having to do with murky notions like real existence and concreteness. 4. A deterministic event E is one that is (nomically) determined by some cause of E. 5. A stochastic, or random, event is one that is not deterministic. Thus, by definition, either it has no cause, or it has a cause that fails to determine it. 6. A chancy event is one that has a precise physical chance that differs from 0 and 1. Since a deterministic event has a chance of 1, chancy events are all random. Now the Mistake is plain. Suppose that random events are uncaused. Then, in particular, chancy events are uncaused. This is an absurd claim. If a chancy event (such as the decay of an atomic nucleus) has no ontological source, then where does its precise chance come from? It is well known that some types of nucleus are much more stable than others (eg. copper 63 has a much lower chance of decay than copper 62). Surely these chances then arise from the physical structures of the nuclei? The absurdity is heightened when one considers a large set of similar stochastic experiments. As is well known, in a large set of trials one reliably obtains relative frequencies 3

4 of outcomes that approximate their physical chances. Now, if each random outcome is uncaused, or from nowhere, then so is the entire set. Yet the aggregate is quite reliable, and predictable, in some of its properties. It is hardly reasonable to say that such predictable events appear from nowhere. For example, the familiar interference fringes of the double slit experiment arise as the aggregate of a large set of random outcomes. Yet these fringes are not only predictable, but their size and shape is derivable from some physical properties of the experimental apparatus, such as the wavelength of the photons and the separation of the slits. One can continue in this vein, giving examples of stochastic experiments where there are obvious causal connections between the experimental set up and its outcomes, but I think the point is clear. The outcomes of these experiments, while random, are produced by the apparatus. They do not appear from nowhere! I will consider two possible responses to this (rather trivial) argument. First, that in the kind of experiment I m discussing the outcomes are not truly random; the probabilities the physicists talk about are really epistemic, as the underlying process is actually deterministic. Second, one might respond that in these experiments the outcomes are not wholly uncaused, as the apparatus is a partial cause. But they are still not fully caused, as deterministic events are. If the first objection is correct then there are in fact no chancy processes, according to our definitions above. Moreover, for the objection to succeed, the very idea of positing a chancy cause for something like an interference pattern must be incoherent! Physicists will hotly contest this, of course, for two reasons. First, no other type of explanation for such phenomena is known to exist. (Attempts to provide a deterministic foundation for stochastic mechanics all run into the same difficulty of trying to introduce probabilities without a random process.) Second, the Bell inequality and the Aspect experiments are thought to show that quantum mechanics is maximal, 4

5 and that the probabilities are ultimate and irreducible. If a philosopher wants to say that this view (as well as a basic mode of explanation in physics) is incoherent, a very strong argument is needed. Unfortunately the philosopher has no argument at all, just a stubborn insistence that causes determine their effects. The second objection is inconsistent with the definition of a total cause given above. When you gather together all the partial causes, what you get is by definition the total cause. But perhaps that definition is unsuitable. Perhaps, in the case of a random event, the collection of its partial causes has something missing it is not sufficient, perhaps? The word sufficient here can be read in two ways. The claim might be that the partial causes are not ontologically sufficient to produce the effect. But this false the effect is there, and these causes alone did it. The other reading is that the partial causes are not nomically sufficient to determine the effect. This is true, of course, since the event is random, but we are talking about causation here, not determination. I cannot find any reasonable sense in which the collection of partial causes of a random event is somehow less than a total cause. 2. Why It Matters We have seen that it is a mistake to claim that random events are uncaused, or (equivalently) that fully caused events are always deterministic. But why does this really matter? What are the consequences of this error in the free will debate? 1. If the Mistake is corrected, then the only serious argument for determinism disappears. This argument starts with the plausible premiss that every event has a cause, and then uses the Mistake to infer that every event has a cause that determines it. 5

6 (The other common argument for determinism, that the physics we know is deterministic, is mystifying. The most fundamental physical theory we have, namely quantum mechanics, is indeterministic. This obvious fact tends to be dismissed with the erroneous claim that the randomness in quantum theory is confined to the atomic level and below. Quantum mechanics actually claims the exact opposite of this. Small systems (like atoms) evolve deterministically, following the Schrödinger equation. It is only a measurement made on the system that has a random outcome and a measurement is, of course, a macroscopic event. From a quantummechanical point of view, it is likely that the familiar deterministic systems are only approximately so, and that such systems are rather rare in nature.) 2. If the Mistake is corrected, then one of the main arguments for compatibilism is seriously weakened. The compatibilist argues, quite reasonably, that free choices should be caused internally, by one s own beliefs and desires, character and so on. (A libertarian should agree with this.) The compatibilist then mistakenly infers that since the free action is caused, it must be determined. An indeterministic event, it is falsely claimed, would be uncaused, an event from nowhere, and so would not belong to the agent at all; it certainly would not be a free action of the agent. The libertarian claims that the compatibilist s version of free will is a dismal pretence, a pale imitation of the real thing. Using the Mistake, however, the compatibilist seems to turn the tables on the libertarian by showing that the concept of indeterministic freedom is incoherent. While the compatibilist s freedom might look rather flimsy, if the only alternative is incoherent then we had better all accept it! 6

7 3. If the Mistake is corrected, then the need for libertarians to peddle an obscure and panicky (as Peter Strawson put it) metaphysical theory disappears. Unintelligible ideas such as agent causation can mercifully be confined to the waste paper basket. This is not to say that it will then be straightforward to construct a libertarian account of free will, but the logical space for one will have been cleared. For a start, the libertarian can colonize much of the ground currently occupied by compatibilists, pointing out the need for the act to be voluntary, caused by the agent s character, and so on. The action must not, however, be determined by any prior causes outside the agent, or even by events inside the agent before the choice is made. It is the agent s decision that causally determines the action. A libertarian should be wary of the view that free actions have precise chances, as random events in physical experiments seem to. For one thing there seems to be no argument for it, as far as I am aware. Moreover, it is implausible that free actions have probabilities. Indeterminism is a negative concept, being the negation of determinism, so it likely covers a lot of territory (as negative concepts almost invariably do). 4. With the Mistake laid aside, some headway can even be made against the main weapon in the compatibilist s arsenal, the Luck Argument. The Luck Argument aims to show that it is impossible for an indeterministic system to have free will, since it lacks sufficient control over its own behaviour. The argument goes badly wrong, however, in assuming that every indeterministic system has a set of precise possible states. This is extremely unfortunate since, among causal systems, this property entails determinism! (This is easily demonstrated. See, for example, One might as well, in 7

8 trying to prove a general result about circles, assume that every circle has at least one vertex. Any such argument will be unsound. 8