Given the pervasive moral disagreements there are (or seem to be) between different people and different societies, one might question the notion that there are any uncontroversial instances of moral knowledge. In opposition to this, I propose that there is at least one instance of moral knowledge that I think most will find uncontroversial. Suppose, as I believe to be the case, that skipping pebbles across a pond is a morally neutral action: it is neither right nor wrong, but merely permissible. Nevertheless, suppose that Sam, for whatever reason, forms the belief that skipping pebbles across a pond is wrong. (Perhaps Sam’s brain has been hit by one too many cosmic rays.) If, in spite of this, Sam skips a pebble across a pond, he has acted wrongly, even though actions of that type are not normally wrong. No matter what else one may think about which actions—or types of action—are wrong, one must hold that if someone performs any action which they believe to be wrong they have acted wrongly. And if we know that anything is wrong, we know that doing something which one believes to be wrong is wrong.
Or so I think. But you may disagree; and if you do, I’m interested to hear where you think I’ve gone wrong.