Knowledge in an Uncertain World by Fantl Jeremy & McGrath Matthew

Author:Fantl, Jeremy & McGrath, Matthew [Fantl, Jeremy]
Language: eng
Format: mobi
Publisher: OUP Oxford
Published: 2009-11-04T16:00:00+00:00

8 THE BAYESIAN CHALLENGE

According to Bayesian epistemology, belief is fundamentally a graded matter rather than a binary one in this sense: fixing a subject’s graded beliefs is enough to fix her binary or outright beliefs, but not vice versa. A natural conclusion to draw from this is that the justification of graded beliefs is more fundamental than the justification of outright beliefs, again at least in the sense that fixing the justification of the former is enough to fix the justification for the latter, but not vice versa.20

Bayesian epistemologists may disagree about whether there are outright beliefs at all (Jeffrey 1992), and even if they do accept such beliefs they can disagree about how precisely the two sorts of belief are related. But they will reject any view under which your outright beliefs can float free of your total state of graded opinion, as well as one which takes the justification of outright beliefs to float free of the justification of graded opinion.

Our project, like most projects in mainstream epistemology, focuses on the epistemology of outright belief, on justification for believing, and on knowledge. It is not uncommon for Bayesians to grumble about this focus. After all, as they see the psychology and the epistemology, all the real action concerns graded belief. Focusing on outright belief, to the exclusion of graded belief, doesn’t merely sideline the more fundamental reality, it risks mistakenly treating outright belief and its epistemology as fundamental and thereby drawing incorrect conclusions about outright belief.

For instance, a mainstream epistemologist might think, as many have, that outright beliefs must answer to the laws of logic, because logic has normative force over our doxastic lives. But if this leads one to hold that your beliefs must be consistent if you are to be rational, one is forgetting that there is an alternative: logic might well have its normative force on our doxastic lives in the first instance by constraining our graded beliefs. Its normative force, such as it is, for outright belief might merely reflect outright belief’s dependence on graded belief, and not support the strong claim that outright beliefs must be jointly consistent on pain of irrationality. This, at least in broad strokes, is one of the main points for which David Christensen (2004) argues.

Mainstreamers often brush off such worries on the ground that whatever is being said about outright belief can be extended mutatis mutandis to graded belief. For instance, evidentialists might suggest that their talk of doxastic attitudes fitting the evidence extends to graded beliefs (they, too, can fit the evidence), and coherentists might point to the extensions of logical and explanatory coherence for graded beliefs. In many cases it will be reasonable to think the extension won’t introduce fundamental changes, but only complicate the picture.21 The rationale for focusing on outright belief is simply that the added complications of telling the full Bayesian story are beside the particular epistemological point being made. If the issue is whether the justification for beliefs is evidentialist or externalist,

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