(I posted the identical question on the AskPhilosophy subreddit.)
I first learned about phenomenal conservatism under a different name, “the principle of credulity”, from the philosopher of religion Richard Swinburne. (I think there might be some subtle differences between the two, but Swinburne acknowledges their similarity in his book Epistemic Justification, so let’s not be too picky.) I’d paraphrase my understanding of it like this (call it PC1):
If it seems to S that P, then, in the absence of defeaters, S thereby is justified in believing that P
But in the IEP article on phenomenal conservatism, Huemer formulates it like this (call it PC2 - emphasis mine):
If it seems to S that P, then, in the absence of defeaters, S thereby has at least some justification for believing that P
What's the motivation for the bolded part - why only some justification? Some justification might increase my prior credence in P from 0.1% to a posterior credence of 1%, but P surely still isn’t justified? Is there a particular problem that PC1 has that PC2 doesn’t?
Also, elsewhere in the IEP article, it looks like Huemer speaks as though phenomenal conservatism is actually PC1. In section 3.d. he writes:
Enter phenomenal conservatism. Once one accepts something in the neighborhood of PC, most if not all skeptical worries are easily resolved. External world skepticism is addressed by noting that, when we have perceptual experiences, there seem to us to be external objects of various sorts around us. In the absence of defeaters, this is good reason to think there are in fact such objects (Huemer 2001). Moral skepticism is dealt with in a similarly straightforward manner. When we think about certain kinds of situations, our ethical intuitions show us what is right, wrong, good, or bad. For instance, when we think about pushing a man in front of a moving train, the action seems wrong. In the absence of defeaters, this is good enough reason to think that pushing the man in front of the train would be wrong (Huemer 2005). Similar observations apply to most if not all forms of skepticism. Thus, the ability to avoid skepticism, long considered an elusive desideratum of epistemological theories, is among the great theoretical advantages of phenomenal conservatism.
Maybe skepticism is easily resolved on PC1, but on PC2 the skeptic could still say that sure, it provides a little bit of justification, but not much.
Why formulate phenomenal conservatism as PC2 over PC1? What am I missing?