You can't get an "ought" from an "is" — Hume's hidden trap

In 1739, David Hume noticed a sleight of hand running through nearly every moral argument he read. Writers would spend pages describing how the world is — what's natural, what God commands, what humans typically do — and then, without warning, switch to claims about what we ought to do. Hume pointed out that this jump is never logically justified: no pile of purely factual, descriptive premises can, by itself, force a conclusion containing a moral "should." This is the is–ought gap (sometimes called Hume's guillotine).

The key move is subtle. "Humans evolved to eat meat" is a fact. "Therefore eating meat is morally fine" is a value judgment — and it simply doesn't follow unless you smuggle in an extra premise like "whatever we evolved to do is permissible." That bridging premise is itself a value claim that needs its own defense. Point it out, and the argument suddenly looks a lot less obvious.

This is why appeals to "it's only natural" or "that's just how things are" so often mislead. Nature is full of parasitism, infanticide, and disease; the mere fact that something occurs tells you nothing about whether it's good. Recognizing the gap doesn't mean facts are irrelevant to ethics — it means facts alone are never the whole argument. Somewhere, a value has to be doing the work.