This is the first of six posts in my essay on free will.
Determinism holds that every event, including every action and every decision, has a cause. Furthermore, determinism holds that such causes can, at least in principle, be fully explained by deterministic physical laws.
This situation is demonstrated graphically in Figure 1. An individual has a particular brain state at time t1 determined by her genetic make-up and her history of personal experiences. Put differently, her unique mixture of “nature and nurture” give rise to her brain state. Let us say she makes a decision at time t1, in which she must choose from among a group of different options. In the deterministic framework, the combination of her brain state and the set of available options cause her to choose one particular option: the inputs (the brain state and the set of available options) uniquely determine the output. No other outcome is possible given exactly the same brain state and the same set of available options. Rewinding the clock and letting it run again to time t1 will result in exactly the same set of inputs as before, and therefore exactly the same outcome. However, if we let the clock continue to run, and present the same choice to the individual at some later time t2, the outcome may be different because the brain state, and therefore one of the inputs to the decision-making process, is likely to have changed (the individual will have accrued additional personal experiences since t1).
Can we predict someone’s decisions ahead of time? Determinism holds that, in principle, if we know the current brain state of the individual, and the set of choices presented to him, then we can accurately predict what decision he will make. However, it is important to emphasize that such a prediction can only be made moments before the actual decision is made. Furthermore, knowing the complete brain state of an individual is a task vastly beyond our current technological capabilities.
If we wish instead to predict someone’s behavior days or years from now, including any decisions they may make, we have a practically impossible task ahead of us, even though it might be theoretically possible. This task would require that we know not only the current brain state of the individual, but the current state of that individual’s surroundings also. This is because the individual’s surroundings will influence his brain state over time. We must therefore be able to predict changes in the surroundings if we are to predict changes in our individual’s brain state. But where do we draw the boundary of these surroundings? In today’s world, most individuals are influenced, either directly or indirectly, by events taking place all over the world. Even the simple task of eating often involves food or utensils imported from other countries. Therefore, in order to predict the evolving brain state of an individual, which depends on what nutrients the brain has absorbed, we must be able to predict when and where these nutrients will appear, and so we must be able to predict, for instance, the growth of crops in foreign countries. This, in turn, requires us to accurately predict the weather everywhere on the globe which, due to chaotic processes, is essentially impossible. And this is just one chain of influences acting on an individual’s brain. It seems clear, then, that the full task of predicting a person’s behavior at any significant time into the future will always remain intractable.
If the theist is troubled by the possible predictability of human choice, she should note that some theists have actually embraced such a concept: Calvinists promote the idea of predestination, which holds that God has foreordained every decision we will make, including whether we will accept or reject him, and therefore be sent to heaven or hell.