In practice the term "determinism" encompasses a wide range of viewpoints. First, determinists disagree about what agents are supposed to determine human action—heredity, environment, or some combination of these and perhaps other factors. These differences give rise to arguments such as the "nature versus nurture" debate, from which the alternative of individual self-direction is conspicuously missing. Second, determinists define their philosophical positions in various ways, propounding various species of "hard" and "soft" determinism. Many "soft" determinists seem to acknowledge, in some form and to some degree, the capacity of a human being to select among alternatives in mental processes, and consequently in physical actions. Recognition of such a capacity will be essential to the analyses in this course, where it is called volition or free will. Although the term "free will" is sometimes assigned supernatural connotations, here it refers to a natural human capacity, known to us from everyday experience.

Typically, the "soft" determinist is reluctant to describe human choice as "free will," claiming that our experience of making choices freely is illusory because our thoughts and choices are necessitated by either (1) unrecognized outside forces or (2) logical necessity.