Is Morality Natural?

Knowing Right From Wrong --

But how can morality be a natural phenomenon? We ought not to boil babies, but the natural world seems not to contain any trace of an "ought," or an "ought not." A dropped stone is under no obligation to fall, it just does. Admittedly, I might say, before dropping a stone out of the window, "This stone ought to hit the ground in three seconds," but here I just mean something like "It is likely that the stone will hit the ground in three seconds." If the stone doesn't do that, it has done nothing wrong, and is not to be blamed for anything. In the natural world, nothing ought to happen, or ought not to happen, in the relevant sense of "ought." Keeping within the confines of nature, there is no space for the fact that we ought not to boil babies. Yet since nature is all there is, there is no place left to go.