All things that happen are part of a causal chain starting from first principles and mushrooming out to the unbelievable complexity of life on earth.
Humans, as much as any other constituent of this profusion, are 'things that happen'.
It follows, then, that the course and development of this causal river can theoretically be worked out mathematically, and that all processes on earth, including personality, human decision and the workings of the brain generally, are likewise determined and (theoretically) predictable.
This appears to deny the existence of free will, and to set up a directly oppositional stance towards it that has repercussions all over; in the conflict between religion and science, for example, and in ethics and epistemology generally.
There are some very good arguments for determinism as opposed to free will, and some fairly good ones for free will as opposed to determinism. But I am proposing neither. Instead I am attempting a middle course: I want to prove that free will and determinism are two names for the exact same thing, and the friction between them, however real it may seem to their respective advocates, is a spurious one that basically comes down to use of language.
I am not here proposing a model of Consilience, nor attempting to bypass enquiry with a kind of complacent pop-Positivism.
Nonetheless, rightly wary as we should be of the relegation of all philosophical enquiry to debate about the linguistic assumptions and underpinnings of scientific enquiry, it is surely inarguable that genuine confusion can result from the imprecise or variant use of terms and concepts.
Just such a confusion has occurred here, with the religious sense and man's broader fear of spiritual and evolutionary relegation muddying the waters still further.