In his Philosophical Explanations, 1981, Robert Nozick sketched a view of how free will is possible, how without causal determination of action a person could have acted differently yet nevertheless does not act at random or arbitrarily. (He admits the picture is somewhat cloudy.)
Despite approaching the problem from several different directions, he found it so intractable, so resistant to illuminating solution, that he was forced to conclude “No one of the approaches turns out to be fully satisfactory, nor indeed do all together.”
Nozick admits that “Over the years I have spent more time thinking about the problem of free will — it felt like banging my head against it — than about any other philosophical topic except perhaps the foundations of ethics.”
Nozick introduces quantum mechanics to consider an analogy with the weighting of reasons for a decision. He does not, however, claim any applicability to the decision process or free will, since this would just be a random decision.
Is this conception of decision as bestowing weights coherent? It may help to compare it to the currently orthodox interpretation of quantum mechanics. The purpose of this comparison is not to derive free will from quantum mechanics or to use physical theory to prove free will exists, or even to say that nondeterminism at the quantum level leaves room for free will. Rather, we wish to see whether quantum theory provides an analogue, whether it presents structural possibilities which if instanced at the macro-level of action — this is not implied by micro-quantum theory — would fit the situation we have described. According to the currently orthodox quantum mechanical theory of measurement, as specified by John von Neumann, a quantum mechanical system is in a superposition of states, a probability mixture of states, which changes continuously in accordance with the quantum mechanical equations of motion, and which changes discontinuously via a measurement or observation. Such a measurement “collapses the wave packet”, reducing the superposition to a particular state; which state the superposition will reduce to is not predictable.” Analogously, a person before decision has reasons without fixed weights; he is in a superposition of (precise) weights, perhaps within certain limits, or a mixed state (which need not be a superposition with fixed probabilities). The process of decision reduces the superposition to one state (or to a set of states corresponding to a comparative ranking of reasons), but it is not predictable or determined to which state of the weights the decision (analogous to a measurement) will reduce the superposition. (Let us leave aside von Neumann’s subtle analysis, in Chapter 6, of how any placing of the “cut” between observer and observed is consistent with his account.) Our point is not to endorse the orthodox account as a correct account of quantum mechanics, only to draw upon its theoretical structure to show our conception of decision is a coherent one. Decision fixes the weights of reasons; it reduces the previously obtaining mixed state or superposition. However, it does not do so at random.