Tarik is correct. Derek Parfit, an Oxford scholar whom is widely considered one of the most important and influential moral philosophers of the late 20th and early 21st centuries. , in 2011 produced a massive work on ethics titled On What Matters. This two-volume work covers a lot of ground, but one of its main claims is that morality is objective, and we can and do know moral truths but not because moral judgments describe some fact. Indeed, moral judgments do not describe anything in the external world, nor do they refer to our own feelings. There are no mystical moral or normative entities. Nonetheless, moral judgments express objective truths. Parfit’s solution? Ethics is analogous to mathematics. There are mathematical truths even though, on Parfit’s view, there are no such things as an ideal equation 2 + 2 = 4 existing somewhere in Plato’s heaven. Similarly, we have objectively valid moral reasons for not inflicting pain gratuitously even though there are no mystical moral entities to which we make reference when we declare, “Inflicting pain gratuitously is morally wrong.” To quote Parfit, “Like numbers and logical truths … normative properties and truths have no ontological status” (On What Matters, vol. 2, p. 487).
As I understand it, Parfait seems to think that moral judgments are strictly a priori. Then why is he assuming that we make no references in moral judgments? If I'm standing next to a river I think it would be impossible for me to reason (a priori alone) that I'd drown in the river. I would need empirical evidence of drowning, such as testing myself to breathe underwater. I simply don't get your source. How would I arrive at a purely a priori conclusion that throwing a person in the river would kill her?
