(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?

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    He explains the distinction in the Objections section (emphasis his):"a belief with extremely serious practical consequences may call for a higher degree of justification and a stronger effort at investigation than would be the case for a belief with less serious consequences. PC only speaks of one’s having some justification for believing P; it does not entail that this is a sufficient degree of justification for taking action based on P." In other words, Huemer does not use Bain's strong notion of belief as "that upon which a man is prepared to act". His "belief" is belief-light.
    – Conifold
    Jan 31, 2021 at 0:33
  • @Conifold Ha, I read the whole thing but completely missed that. This is helpful, thank you! Jan 31, 2021 at 15:29
  • Even with this, I share your concern about this stance's effectiveness against skepticism. Skeptics typically raise doubts about knowledge, and those would seem to come back anyway once we try to pass from belief-light to belief full flavor, as we must to act. So they are merely shifted, not avoided. This reminds me of Russell's quip:"The method of 'postulating' what we want has many advantages; they are the same as the advantages of theft over honest toil." Believing what seems to us isn't very far from postulating what we want.
    – Conifold
    Feb 1, 2021 at 5:49
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    @Conifold re actions, I thought he meant when you do the decision theory calculations, certain actions can have such negative utility (harm that you cause to others, etc.) when you're wrong, and this would far outweigh the positive utility weighted by the probability that you're right. But if you increase the probability that you're right (going beyond appearances and looking for extra evidence), then the action can have positive expected utility. (I can give an example but I'm sure you know what I mean.) Sometimes you only need a very low credence in something to act if "the odds are right". Feb 1, 2021 at 21:51
  • @Conifold [Part 2] If justification is a matter of degree, then really the line between justified and unjustified belief is kind of arbitrary semantics (i.e. we should just stick to stating quantitative credences). Given all this, I thought he formulated PC as 'appearances give some justification in the absence of defeaters' because he didn't want to commit to saying exactly how much, and where to draw this line between justified and unjustified belief. That was my (eventual) takeaway. Feb 1, 2021 at 22:17


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