One kind of proof is a logical demonstration. You start with some assumptions and deduce a conclusion. Mathematics is the ancient model here. We all did it in geometry. Can we do this in morals? I don't know for sure. I'm intrigued by the possibility of deducing a moral principle from an analysis of moral concepts. As a libertarian I care about the basis for individual rights, but I don't know for sure whether they can be supported in this way.

Another kind of proof is used in natural science. Lots of data, or perhaps a single critical piece of data, is gathered in order to support some hypothesis. Again, can we do this in morals? I'm not sure. Suppose we gathered lots of data on different societies and created a science of ethics. What would it tell us? Could it tells us what we should do? That seems doubtful to me.

One sort of moral proof might consist of pointing out the consequences of an action. If a set of principles are agreed to, then this may function as a proof in a particular case. But what if the principles are not agree to? In the cases we are talking about, there is likely to be fundamental disagreement. The disagreement probably doesn't turn on consequences.

Another kind of proof might derive a principle from a higher principle. Sometimes we can do this in morals. But does that do anything more than move the problem to a higher level?

Proof seems elusive. Is there an answer?