You've made essentially this argument yourself, and I've been wondering: How is causal determinism "presupposed in the concept of human action"?
Can't I do things without the results being guaranteed?
You're misreading the quote, I think. Hill isn't talking about the planned results of one's action being "guaranteed" or determined, but rather simply stating that action itself is impossible without some form of causality.
In the quote Hill seems to be assuming that any form of causality would be in some way deterministic, which makes sense to me. Whether or not you agree with it is another question.
EDIT: Another way to think about it is that the determinism Hill is referring to doesn't have to do with whether certain results are guaranteed (as y...
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