My dictionary has the following:
Determinism: The philosophical doctrine that every event, act, and decision is the inevitable consequence of antecedents, such as physical, psychological, or environmental conditions, that are independent of the human will.
Predestinate: 1. To destine or determine in advance: foreordain.
So, there is a philosophical difference between the two: predestination happened before the event, and determinism happens at the time of the event. And, theologically speaking, at least according to Calvinism, the only thing predestined is one's salvation. One's decisions in this life may reflect one's grace (or not
), but they are still one's own decisions.
In any case, I'm still not buying either one. No chemical process compelled me to write this post denouncing my enslavement to chemical processes!