Determinism is not just causality. Determinism goes far beyond causality, and certainly much farther than psychological science requires.
Many scientific psychologists embrace determinism without realizing what it means. That, at least, is the distinct impression left with me after the dramatic debate about free will at the keynote session of the big annual conference of the Society for Personality and Social Psychology in Tampa earlier this month.
Plenty was said to support determinism - but it seemed quite irrelevant. The gist seemed to be, in psychology we study causes, so we have to believe in determinism. This is wrong to the point of silly.
Determinism is a belief in the inevitability of causation. Everything that happens is the only possible thing that could happen. The chains and networks of causes are so powerful and inexorable that every outcome is inevitable. We are already locked in to everything else that is going to happen in the entire future of the universe. If you knew all the causal principles and had enough information about the present, you could predict the future with 100% accuracy. The universe resembles a giant machine, grinding alone exactly as it must inevitably continue to do, following rigid rules. That is determinism.
To a determinist, there are no counterfactuals. Nothing that didn't happen could possibly have happened. Everything that did happen was the only possible thing that could have happened at that point in time and space, given the causes.
That is why determinism and free will strike most people as incompatible beliefs (even though in recent decades a growing group of philosophers have embraced some form of ‘compatibilism' that preserves a watered-down notion of free will while also embracing determinism). The essence of free will is that the person really could do more than one possible response to a given situation. To a determinist, that is wrong. Causes, including unconscious causes, are operating to bring the person inevitably to what he or she will eventually do. The appearance of multiple options is an illusion, to a determinist.
To a determinist, all choice is illusory. The literal meaning of choice is that there are multiple options, and the person selects one of them. Thus, choice requires multiple possible outcomes, which is a no-no to determism. To the determinist, the march of causality will make one outcome inevitable, and so it is wrong to believe that anything else was possible. The chooser does not yet know which option he or she is going to choose, hence the subjective experience of choice. Thus, the subjective choosing is simply a matter of one's own ignorance - ignorance that those other outcomes are not really possibilities at all.
To illustrate: When you sit in the restaurant looking at the menu, it may seem that there are many things that you might order: the fish, the chicken, the steak, the onion soup. Eventually you will make a selection and eat it. To a determinist, causal processes dictated that what you ordered was inevitable. When you entered the restaurant you may not have known, yet, that you would end up ordering the chicken, but that simply reflects your ignorance of what was happening in your unconscious mind. To a determinist, there was never any chance at all that you could have ordered the fish. Maybe you saw it on the menu and were tempted to get it, and maybe you even started to order it and then changed your mind. No matter. It was never remotely possible. The causal processes that ended up making you order the chicken were in motion. Your belief that you could have ordered the chicken was mistaken.
Belief in inevitable causality may seem like an extreme or straw-man idea, but it is not. Many people have believed this. It is inherently consistent and plausible. It may be wrong, but it is not absurd.
For psychological science, however, a belief in choice seems more plausible and useful than determinism. Choice is fundamental in human life. Every day people face choices, defined by multiple possibilities. To claim that all that is illusion and mistake is to force psychological phenomena into an unrealistic strait jacket.
Also, psychological causality as revealed in our labs is arguably never deterministic. Our studies show a change in the odds of one response over another. But changes in the odds entail that more than one response was possible. Our entire statistical enterprise is built on the idea of multiple possibilities. Determinism denies the reality of this. Statistics are just ways of coping with our ignorance, to a determinist - statistics do not reflect how reality actually works.
To believe in determinism is thus to go far beyond the observed and known facts. It could be true, I suppose. But it requires a huge leap of faith, as well as a tortuous effort to deny that what we constantly observe and experience is real. Instead, I think psychological science is better suited to a belief in indeterminacy. As far as I can tell, there is no proof of any deterministic causality anywhere. That is, there is no proof that any result is 100% inevitable, though in practice some things seem to be very highly reliable. When I turn on the light switch, the light pretty much always comes on, unless some other causal factor (e.g., burned-out lightbulb, power failure) prevents it. Still, there is no way of saying whether this is 100% inevitable or simply a very high probability. Indeterminacy lurks at the subatomic level, and once in a very long time this could show up at the macro level. In human behavior, of course, things are not nearly so reliable or predictable. Hence accepting the reality of choice amid genuinely multiple possibilities seems a more prudent and useful basis for psychological theorizing than deterministic inevitability.