God Isn't the Only Moralist Around!

Two things,” Immanuel Kant wrote in the late 18th century, “fill the mind with ever new and increasing admiration and awe, the more often and steadily we meditate upon them: the starry firmament above and the moral law within.”
The awesome starry firmament inspires plenty of controversy—about the composition of dark matter, for example. But a lot is known: the sun is composed of hydrogen and helium, the Horsehead Nebula is 1,500 light years distant, and so on.
There’s also plenty of controversy about moral law. Should we give much more to charity than we actually do? Is torture permissible under extreme circumstances? Is eating meat wrong? Could it ever be permissible to kill one innocent person in order to save five? But, again we know a lot. Throwing good taste out with the bathwater for the sake of a clear example, everyone knows that boiling babies for fun is wrong. Boiling lobsters is a matter that reasonable people may disagree about, but as far as boiling babies goes, agreement is pretty much universal. Babies suffer when boiled—they are not like the worms that live near undersea vents, who are partial to scalding water. If something goes without saying, it’s this: one ought not to boil babies for fun.
Apart from filling the mind with admiration and awe, the starry firmament and the moral law together fill the mind with a problem, which Kant’s remark obscures. The quotation suggests, misleadingly, that the astronomical and moral realms are wholly separate—the former is “above” and the latter is “within.” But they aren’t: as Moby correctly sings, “We are all made of stars.” The heavens and human beings are composed from the same physical stuff, and are governed by same physical principles. The starry firmament isn’t really “above”—it’s everywhere. We, along with lobsters and the rest, are part of it.
Everything, in short, is a natural phenomenon, an aspect of the universe as revealed by the natural sciences. In particular, morality is a natural phenomenon. Moral facts or truths—that boiling babies is wrong, say—are not additions to the natural world, they are already there in the natural world, even if they are not explicitly mentioned in scientific theories. Fundamental sciences such as particle physics and molecular biology do not speak explicitly speak of sand dunes, or boiling water, or lobsters, but facts about sand dunes and the like are implicitly settled by more fundamental facts: arrange bits of matter a certain way and you have an eroding sand dune, or boiling water, or (here the arrangement needs to be very complicated indeed) a lively lobster. And, presumably, the same goes for the moral facts.
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.
This problem is sometimes traced to David Hume’s Treatise of Human Nature, in which Hume, writing half a century before Kant, complained of an “imperceptible change” from “the usual copulations of propositions, is, and is not” to propositions “connected with an ought, or an ought not.” “This change,” Hume said, is “of the last consequence. For as this ought, or ought not, expresses some new relation or affirmation, ’tis necessary that it shou’d be observ’d and explain’d; and at the same time that a reason should be given; for what seems altogether inconceivable, how this new relation can be a deduction from others, which are entirely different from it.”