Is Moral Nihilism a Morality?

[SenseMaker007]

All a priori knowledge is non-natural.

Well, it is if you define it that way. I just think of the whole of the universe is natural and I don't see how we can have knowledge of something that is not part of the universe.

Truth can be entirely a priori because the truth is still true even if we don't exist to experience it. But how can we know something without being aware of it? So isn't even a priori knowledge also fundamentally a posteriori at least in the sense that we have to experience the a priori truth in order to know it?

The point I was trying to make was that there is a such thing as non-natural knowledge. A priori knowledge is a perfect example.

But if non-natural knowledge is just a synonym for a priori knowledge then isn't that a meaningless distinction?

But other than to demonstrate that non-natural knowledge is a thing, the a priori/a posteriori distinction is not identical with the natural/non-natural distinction.

Okay, so if it's not identical, then what's the difference? How does non-natural knowledge differ from a priori knowledge (and perhaps I can just ignore my quibble regarding the impossibility of entirely a priori knowledge, for the time being).

A non-naturalist simply holds that moral facts aren't the same as natural facts.

In what way do they differ if the whole universe is natural?

A non-naturalist rejects that moral principles can be solely perceived by empirical investigation. In the simplest terms, the non-naturalist says (correctly, I think) that no amount of empirical investigation (by itself) will reveal a moral fact.

But does "not empirically verifiable" really mean "non-natural"?

And if that is what non-natural means ... then it would seem that non-natural is indeed identical in meaning to a priori ... because a priori equally refers to knowledge that is not empirically verifiable.