Ever since Hume, lots of people have been very worried about the is/ought gap — the notion that there’s an unbreachable divide between descriptive claims and normative claims. The basic idea is that, because you can’t derive an ought from an is, there can’t be moral facts — after all, we can’t prove a prescriptive fact from the merely descriptive claims we know about the world.
However, I don’t think that this is a problem at all. To see this, let’s consider the two types of moral realism.
One type is moral naturalism. Moral naturalism says that moral facts are some complex type of descriptive fact. So, much like water is just H20, the moral facts are just some type of complex fact about what is. Maybe morality is what impartial ideal observers would approve of. Or perhaps morality is some irreducible higher-order property — this is what Cornell Realists think.
If one is a moral naturalist, it’s not hard to see why the is/ought gap isn’t a problem. After all, on this account, you can get an ought from an is. Oughts are just a type of is statement. Much like you can deduce facts about water from facts about hydrogen and oxygen, the same is true of getting an ought from an is. Thus, on this account, there is no fearsome, unbreachable gap.
But what about moral non-naturalism which says that moral facts are not reducible to descriptive facts? On this account, knowing all the descriptive facts about the world wouldn’t tell you the relevant moral facts. Moral facts are thought to be somewhat like the laws of logic on this account — not contingent on any physical facts. This would say that moral facts are not descriptive — they’re distinctly about what should be rather than what is.
But for moral non-naturalists, there’s no problem either. This is because moral non-naturalists don’t get an ought from an is. Rather, they argue that we have some way of knowing about non-natural facts. Much like one doesn’t derive the laws of logic from what is, the non-naturalist about morality thinks that you don’t get an ought from an is — there are just certain necessary oughts that aren’t caused by the descriptive facts.
There’s no is/math problem, even though complex mathematical facts don’t come from descriptive facts about the world. This is because mathematical facts don’t need descriptive facts as their source; moral naturalists would say the same is true of normative facts.
Thus, either you can get an ought from an is or you don’t need to because the oughts are necessary and unrelated to physical facts. Either way, Hume’s guillotine need not decapitate our moral realism.