Psychology and Free Will

I’ve long wondered how one could be Christian (or Muslim or Jew) and believe in psychology at the same time. For it seems to me that psychology is the science that studies mental processes--including volitions--and behavior and the conditions that cause them, whereas a cornerstone of Christianity (and Islam and Judaism) is free will. Thus, psychology says that every human choice is caused by antecedent conditions, whereas Christianity says that human choices are not caused by antecedent conditions. That is, no matter what interacting biological, social, cultural, and psychological conditions existed at the time someone made a particular choice, she could have made a different choice than the one she actually made, and if that same set of interacting conditions were to somehow recur, the person in question could choose differently than she did the first time.

This is how I expressed this idea in a recent post to an online forum:

Psychology is the scientific study of mind and behavior. Science presumes that all events have causes which, in turn, have causes, and so on. Thus, psychology presumes that all human mental phenomena, including choices, and all behaviors are caused by something, which, in turn, are caused by something else. Now if choices and acts are caused, they are the inevitable effects of their causes and not free to be other than what they are given the causal conditions giving rise to them. Yet, Christians, on the other hand, believe in some kind of mysterious free or uncaused and uninevitable will that is not caused by anything other than a free--i.e., undetermined--agent. And uncaused human mentation and behavior is not amenable to scientific--i.e., psychological--study and therefore seems incompatible with the fundamental assumption of psychology that human mentation and behavior can be studied scientifically. Thus, I don't see how one can truly be Christian and truly believe in psychology at the same time.

In a subsequent post, I tried to express the argument above the following more concise, logical form:

(1) Science is the systematic study of phenomena and
their causes.

(2) Psychology is the science that studies the
phenomena and causes of the phenomena of mentation, including will, and
behavior.

(3) Free will is uncaused will.

(4) Therefore, psychology and free will are
incompatible.

(5) Christians believe in free will.

(6) Therefore, Christianity and psychology are
incompatible.

Again, I don’t understand how Christians can believe in psychology. Nor do I understand how so-called forensic psychologists can testify for the prosecution in court that someone could have chosen not to commit a crime but went ahead and did it anyway. How could any psychologist or psychiatrist worthy of the name testify to such a thing? As far as I’m concerned, the legal definition of “insanity” as not knowing right from wrong or as being unable to avoid wrongdoing would seem to apply to the psychological and psychiatric understanding of ALL criminal acts. That is, from a psychological or psychiatric perspective, how are ALL criminal acts not insane?