Hume's conception of Nature

After Dr. Davis mentioned his curiosity about what Hume's conception of nature is, I thought I might take a look at it.

Here is his theory about what would happen if all of mankind became Pyrrhonian skeptics:

"All discourse, all action would immediately cease; and men remain in total lethargy, till the necessities of nature, unsatisfied, put an end to their miserable existence... Nature is always too strong for principle." (Chapter 12, paragraph 23)

Nature seems to hold a profound significance in the study of reality for Hume. But it is difficult to say exactly what he thinks nature can tell us about reality. In the above quote, he might be saying that nature would end the miserable existence of the extreme skeptic who does not even satisfy one's craving to eat out of his doubt that hunger-pains are really connected to lack of nourishment in the body, since they have reason to doubt causality.

Hume makes an interesting statement later in the same paragraph, where he says that the "whimsical condition of mankind" is that it "must act and reason and believe," since men are unable to satisfy their understanding of or objections to the operations and foundations of their minds.

If nature in fact does correspond with the law of causality, then how would Hume grant that the human mind is privy to knowledge of reality?