What did David Hume mean when he said that "reason is a slave to the passions"?

Question

I don't understand the meaning of this oft-quoted quotation of Hume's in _On Reason_, namely his saying that "reason is a slave to the passions." What exactly does he mean by that ? Is it simply that reason is subsequent to a deeper moral sense? Is it equivalent to the maxim today that "science cannot answer moral questions"? One thing that may be confusing is me is that I sense he's being somewhat rhetorical; would it be better to summarize his the arc of work that reason can only _guide_ the passions, and that the truths we think it is uncovering us are ultimately a product of what our fickle passions urge it to investigate?

Answer 1

I think it's simply this: Most of us, especially philosophers, would like to think that our views, especially our ethical views, are not the consequence of bias or our psychological temperament, but rather because we have thought carefully and deeply about the issue. In other words, we'd like to think that it is because we are reasonable that we have the views that we have, rather than because we are emotional.

But really, Hume thinks, the emotion comes first and then, because the emotions make us feel right, we come up with the justifications after the fact.