How to prove that some acts are wrong (without using substantive moral premises)

I first argue that there are many true claims of the form: I broken vertical bar-ing would be morally required, if anything is. I then explain why the following conditional-type is true: If phi-ing would be morally required, if anything is, then anything is actually morally required. These results allow us to construct valid proofs for the existence of some substantive moral facts-proofs that some particular acts really are morally required. Most importantly, none of my argumentation presupposes any substantive moral claim; I use only plausible claims that most moral skeptics and error theorists can and do accept. The final section diagnoses why my arguments work. Here, I offer an explanation for the supervenience of the moral on the non-moral that may help those worried that the strategy is a sophisticated trick. I conclude by considering two objections. In replying to these objections, I explain why the strategy may allow us to demonstrate more than "obvious" moral truths, and why it may also address a stronger version of error theory, according to which, moral truths are not possible.