(This article was coauthored with Kathleen D. Vohs and first published in Dialogue, the newsletter for the Society for Personality and Social Psychology, alongside a companion piece by John Bargh and Brian Earp. The Co-Editor, Hart Blanton, requested that we not post the entry until the newsletter appeared, which he estimated would be around July 1. I post it now because colleagues have begun to receive the newsletter. In the next few days, I shall post a summary of my remarks at SPSP, my responses to John Bargh's comments, and further thoughts. Comments are welcome on all of these.)
The recent debate on free will at SPSP led to the realization that some of the ostensible disagreement, and perhaps most of the surplus emotion swept along with it, stemmed from misunderstandings. Many psychologists say it is important to uphold determinism - yet they do not really know what determinism is.
Determinism is more than belief in causality. The defining feature of determinism is a belief in the inevitability of causality. The essence of determinism is that everything that happens is the only thing that could possibly happen (given the past) under those circumstances. The category of the possible and the category of the actual are exactly the same. If you knew everything about the world today and knew all the causal principles, you could calculate everything in the future and the past with 100% accuracy. To a determinist, the universe is just grinding along as a giant machine with no uncertainty whatsoever. The future and the past are both set in stone, so to speak. Check any textbook or handbook of philosophy.
Many psychologists defend determinism thinking that they are defending the notion of causality itself. They think, science studies causes, and if we abandon causation, we cannot do science. But these fears are irrelevant. Everyone believes in causes. The important difference is between probabilistic causation and deterministic causation.
Determinism might or might not be correct. Determinism is impossible to prove or disprove. It directly contradicts the everyday experience of making choices and having multiple options, but everyday experience could be mistaken. In a similar vein, belief in divine or supernatural forces is possibly true, despite inconsistency with daily experience.
We wish, however, to point out some of the mental gymnastics one must go through in order to practice psychological science while maintaining faith in determinism. Let us return for a moment to choice, which has been an important topic of study in social psychology for decades. To a determinist, there is no such thing as actual choice, in the sense of having more than one possible option and making a selection that makes one option come true and makes the others cease to be possible. To a determinist, choice (in this sense) is an illusion, because only one outcome is possible all along. You subjectively believe you might choose A or B or C, but this belief stems from your ignorance. Causal processes are in motion outside of your awareness that will lead inevitably to make you choose B. There was never a chance that you would actually choose A or C. Your belief that A, B, and C are all possible is a mistake; only B is actually possible.
Statistical probability presents a difficult challenge to determinists. The notion of probability entails that different outcomes are possible, which violates the central point of determinism. To a determinist, there are no probabilities in reality. Again, the determinist must say that the seeming indeterminacy simply reflects our ignorance. For example, suppose that when you flip a coin, the outcome is 100% inevitable once the coin is spinning through the air, given the physics of angular momentum, distance to the ground, and so forth. You simply do not know whether it will be heads or tails, so it seems indeterminate to you. The uncertainty is only in your mind.
Notice, however, that this is not how we talk about statistics in our textbooks, courses, and journal articles. We discuss the probability of an event occurring (e.g., by chance), not the gaps in our knowledge. In determinism there is no such thing as chance. To be true to faith in determinism, it would be necessary to alter the way we think about and discuss probabilities and perhaps even to alter the way we use them. (We apologize to determinists for using the word "perhaps," which is itself incompatible with determinism.)
Counterfactual thinking is also incompatible with determinism. It is silly to think "If I had not said those things, we could have avoided the argument" if everything that happened was inevitable. To a determinist, people may think such things, indeed cannot avoid thinking them. Technically, such thoughts might be regarded as sound arguments from false premises. What the person said caused the argument, and so if the person had said something different, the argument might not have happened - but the person could not possibly have said something different, so the entire counterfactual thought process is an idle exercise in futility.
Laypersons often confuse determinism with fatalism, but this is a mistake. Fatalism means that the outcome would have been the same regardless of what you did. To a determinist, the outcome stemmed from what you did, and if you had acted differently, the outcome would have been different. (But, again, you could not possibly have acted differently.)
Some researchers say psychologists should believe in determinism in order to be like so-called real scientists. We believe this is also mistaken. Many natural scientists see the physical world as probabilistic, not deterministic. Quantum indeterminacy would entail that determinism is wrong, by definition. Indeed, as far as we know, there is no proof that there is any deterministic causation anywhere, in the sense that any event is 100% inevitable. Obviously, some causal events have extremely high probabilities, having been demonstrated over and over. But there is no way of knowing whether it is merely well above 99% or it is actually 100%.
The so-called "hidden variables" argument may paradoxically allow determinism to survive in psychology even if it becomes untenable in physics. Here is the issue. If we know everything (mass, velocity, etc.) about a tiny particle, we can predict with certainty where it will go. Every so often, empirical observation shows that it fails to go there. Is this because nature is indeterminate? Or is it because there are hidden variables affecting it, other than the variables we know?
In psychology it is easy to always assume hidden variables when a person's behavior does not conform to predictions, because there are endless additional things that possibly could be known about someone. But with a tiny subatomic particle, there is not much else that could be known, and indeed the set of variables known to physics does not have any room for mysterious other variables.
In conclusion, we think it is possible to maintain a belief in determinism, but it should not be obligatory for psychologists. In fact, psychologists who retain a faith in determinism must keep this an abstract belief and violate it in practice: They must act as if people really make choices, as if multiple possibilities exist for future life, and as if statistical probabilities refer to different possible events. Determinism is not viable in practice but is an elegant theory that people may find appealing as an abstract article of faith. The main alternative to it is a probabilistic universe, in which multiple futures are really possible and causes operate by changing the odds that something will happen rather than guaranteeing it.