I'll try another rephrasing: I have been told that "causal determinism is presupposed in the very concept of human action." I look at the concept of human action and see no presupposition about causal determinism. So I ask, "Where in the concept is this presupposition? I can't find it."
I was also frustrated by Hill's vagueness on what seemed to be an important point (perhaps he elaborates later?). In any case, I can tell you what I think Hill was thinking when he wrote that, though I'm not exceptionally confident about it.
The concept of human action--of making plans and following through with them--seems to be based on the assumption that the world is fundamentally predictable. We make decisions as if the future can to some extent be determined by a knowledge of the present, paired with a set of well-defined rules.
The natural objection...
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