If there are objective notions of good or virtue, you still need to explain why an individual would accept them over their individual preferences. Similarly, if there are objective probabilities in nature, you still need to explain why beliefs should calibrate to them.
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Why AND how - objective probabilities existing in nature can't somehow be known with certainty.
I do sort of think there IS an argument bridging the gap (for example, justification of the Born rule)... but the analogy to the case in ethics is striking.
