In science the word is question-begging; and the only sound rule in science is to beg as few philosophical questions as you possibly can.
Everything in the world is natural, of course, in the sense that things are somehow all akin--all of a piece.

We are simply bound to take in the parts as parts of a whole, and it is just this fact that makes philosophy not only possible but inevitable.

All the same, this fact does not prevent the parts from having their own specific natures and specific ways of behaving.

The people who identify the natural with the physical are putting all their money on one specific kind of nature or behaviour that is to be found in the world.

In the case of man they are backing the wrong horse.