Monday, September 1, 2008

K = JB?

Quick one. There aren't a ton of folks who identify justified belief with knowledge, but I think the number is increasing. At the very least, an increasing number are defending views that seem to carry the consequence that K = JB.

Case in point, consider this passage from Hawthorne and Stanley's, "Knowledge and Action":
Note that an analogous principle seems plausible for reasons for belief, viz: Treat
the proposition that p as a reason for believing q only if one knows that p. One attractive feature of the Action-Knowledge Principle is that it unifies the practical and theoretical domain of reasons: if it is correct, then proper reasons for belief and reasons for action have a uniform nature.


The argument. If a condition necessary for justified belief that p is true is that p is a reason for believing that which is an obvious consequence of it (i.e., justification is closed under known entailment), it would follow that Hawthorne and Stanley are thus committed to the view that knowledge of p’s truth is necessary for having a justified belief that p. After all, p is as obvious a consequence of p as any could be. Is that right?

Update
That might have been a tad terse. The crucial assumption is this:
JC: If S's belief that p is justified, p is a reason for S to believe that which is an obvious (i.e., known with certainty) consequence of p.

This justification closure principle, (JC), gets us JBp --> Kp as follows:
(1) If p is an epistemic reason of S's, S knows p (H&S's view).
(2) If S's belief that p is justified, p is a reason for S to believe that which is an obvious consequence of p (JC).
(3) p is as obvious a consequence of p as anything is (DUH).
(4) If S's belief that p is justified, p is an epistemic reason of S's ((2), (3)).
(C) If S's belief that p is justified, S knows p((1), (4)).

That should be better.

6 comments:

Errol Lord said...

If a condition necessary for justified belief that p is true is that p is a reason for believing that which is an obvious consequence of it (i.e., justification is closed under known entailment)

Is there a typo somewhere in here? I don't understand what this means.

dtlocke said...

Hi Clayton,

Interesting post. But I'm not sure about the 'crucial premise', (JC):

'If S's belief that p is justified, p is a reason for S to believe that which is an obvious (i.e., known with certainty) consequence of p.'

Consider: If Mike's belief that snow is white is justified, then [the proposition that?, the fact that?] snow is white is a reason for Mike to believe that something is white.

Isn't Mike's reason to believe that something is white the fact that *he has a justified belief that snow is white*, and not the fact that *snow is white*? Perhaps I'm missing something here.

BTW, I wouldn't mind if H&S's claim had an absurd implication, as I argue against it, or something they say in defense of it, in a recent post over at Go Grue. Stanley just mentioned you in a comment as someone who might be sympathetic to (part of) my argument. If you have the time, I'd love to hear what you think!

Best,
Dustin

dtlocke said...

Hi Clayton,

Interesting post. But I'm not sure about the 'crucial premise', (JC):

'If S's belief that p is justified, p is a reason for S to believe that which is an obvious (i.e., known with certainty) consequence of p.'

Consider: If Mike's belief that snow is white is justified, then [the proposition that?, the fact that?] snow is white is a reason for Mike to believe that something is white.

Isn't Mike's reason to believe that something is white the fact that *he has a justified belief that snow is white*, and not the fact that *snow is white*? Perhaps I'm missing something here.

BTW, I wouldn't mind if H&S's claim had an absurd implication, as I argue against it, or something they say in defense of it, in a recent post over at Go Grue. Stanley just mentioned you in a comment as someone who might be sympathetic to (part of) my argument. If you have the time, I'd love to hear what you think!

Clayton said...

Dustin,

Good question. I'm somewhat inclined to say that in the closure principle, p is a fact rather than a proposition or propositional attitude.

I suppose you might say that this makes JC implausible. I suppose I might say that from the perspective of H&S, I doubt that they'd balk at JC so understood. That would suggest that they lack a principled reason for refusing to accept JB --> K.

My view, fwiw, is that normative reasons are always facts. I'll try to get a closer look at your post, but it might take a while. I've got a bad week of work staring me in the face.

Best,
Clayton

chrisb said...

Why not just reject the idea that I can treat p as a reason for believing that p?

I know that on one influential account p is evidence for p, but this just follows from the fact that the probability of p/p > probability of p.

Is the following an acceptable principle governing reasons?

(R) If the probability of s/r > probability of s, then r is a reason to believe s.

But I'm not sure you need this anyway. Suppose we limit JC to other cases of mundane entailment (e.g. p v q). If my belief that p is justified, then JC states that p is a reason to believe that p v q. And according to S and H, if I can treat p as a reason, I know that p.

Finally, isn't there room for the view where I can treat p as a reason for believing q, (thus know p according to S and H), believe that q, but fail to know q? In such a situation I can't treat q as a reason to believe, but perhaps it could still be counted as a justified belief. I take it here your argument would be that if it is justified, then it is an epistemic reason. Perhaps, but this seems to be independent of JC.

I'm sure I've said something false above (which is why I hate posting). Feel free to clear up any confusions.

Errol Lord said...

I don't think you need JC to get your conclusion. Here is a simpler argument for your conclusion:

(1) If A justifiably believes p, then p is in the set of A's evidence. (Assumption)
(2) If p is in the set of A's evidence, then A knows p. (from E=K)
(C) Thus, if A justifiably believes p, then A knows p. (from transitivity)

Obviously those who hold E=K but don't hold K=JB must reject (1).