drug_mentor
Bluelight Crew
- Joined
- Jul 12, 2006
- Messages
- 7,538
Evidentialism is the following thesis: An individual S is justified in believing a proposition p at a time t if and only if S's total evidence at t supports the belief that p. More informally, it is the view that the only beliefs one is justified in having are those beliefs for which one has supporting evidence.
It is plausible to think that in many cases belief is not an all or nothing matter, which is to say, there are degrees of belief. With this in mind, a corollary of evidentialism seems to be the following principle, which I will call EC: S's degree of belief that p at t is justified if and only if S's total evidence at t supports her degree of belief that p. So, if ones evidence says that there is an 80% likelihood that a phenomena x will occur at some time t' then one is justified in having a credence of 0.8 towards the proposition that x will occur at t', having a greater degree of confidence would be unjustified.
Evidentialism seems to me an extremely plausible thesis. EC also seems quite plausible, though perhaps overly precise to the point of feeling artificial. I think that, if one accepts these views, then some interesting questions about how to rationally respond to disagreement arise.
Suppose that Amy's total evidence supports a credence of 0.9 towards some hypothesis H, like a good evidentialist, Amy adopts a credence of 0.9 towards H. Now suppose that Amy encounters Berta, someone who Amy knows to be a relatively intelligent person that generally researches the evidence in favour of a hypothesis before accepting or rejecting it. Much to Amy's surprise, Berta is a staunch opponent of H, and on this occasion the two of them vigorously debate whether H is true. Prima facie the fact that a competent reasoner and diligent researcher thinks H is false counts as evidence against H. Reflecting on her present situation, Amy realises that her total evidence with respect to H has increased, and she has accumulated new evidence which should undermine her confidence in H. Being a good evidentialist, Amy worries that she is no longer justified adopting a credence of 0.9 towards H, and adjusts her credence accordingly to 0.8.
Suppose on the following day that Amy encounters Carol, another intelligent person who researches a hypothesis diligently before accepting or rejecting it. Much to Amy's surprise, Carol also rejects H and the two engage in an intractable debate. Later, Amy realises that she has encountered even more evidence against H, and consequently reduces her confidence in H.
There seems to be something quite strange going on here. Evidentialism seems to tell us that the rational response to disagreement with an epistemic peer is to reduce our confidence in the contentious proposition. Perhaps this is reasonable, though, I am not sure (it certainly doesn't conform with the usual practice). A deeper problem seems to be that, if this is right, Amy could conceivably be rationally required to stop having any confidence in H whatsoever, if only she were to happen to encounter enough opponents of H. Presumably, whether those you converse with endorse or reject a particular hypothesis is a contingent matter, and it is not obvious why a series of chance encounters should compel Amy to cease thinking that H is probably true.
What do people think? Is evidentialism plausible? Is moderating one's view the rational response to peer disagreement, or is it perfectly rational to remain steadfast in ones belief?
It is plausible to think that in many cases belief is not an all or nothing matter, which is to say, there are degrees of belief. With this in mind, a corollary of evidentialism seems to be the following principle, which I will call EC: S's degree of belief that p at t is justified if and only if S's total evidence at t supports her degree of belief that p. So, if ones evidence says that there is an 80% likelihood that a phenomena x will occur at some time t' then one is justified in having a credence of 0.8 towards the proposition that x will occur at t', having a greater degree of confidence would be unjustified.
Evidentialism seems to me an extremely plausible thesis. EC also seems quite plausible, though perhaps overly precise to the point of feeling artificial. I think that, if one accepts these views, then some interesting questions about how to rationally respond to disagreement arise.
Suppose that Amy's total evidence supports a credence of 0.9 towards some hypothesis H, like a good evidentialist, Amy adopts a credence of 0.9 towards H. Now suppose that Amy encounters Berta, someone who Amy knows to be a relatively intelligent person that generally researches the evidence in favour of a hypothesis before accepting or rejecting it. Much to Amy's surprise, Berta is a staunch opponent of H, and on this occasion the two of them vigorously debate whether H is true. Prima facie the fact that a competent reasoner and diligent researcher thinks H is false counts as evidence against H. Reflecting on her present situation, Amy realises that her total evidence with respect to H has increased, and she has accumulated new evidence which should undermine her confidence in H. Being a good evidentialist, Amy worries that she is no longer justified adopting a credence of 0.9 towards H, and adjusts her credence accordingly to 0.8.
Suppose on the following day that Amy encounters Carol, another intelligent person who researches a hypothesis diligently before accepting or rejecting it. Much to Amy's surprise, Carol also rejects H and the two engage in an intractable debate. Later, Amy realises that she has encountered even more evidence against H, and consequently reduces her confidence in H.
There seems to be something quite strange going on here. Evidentialism seems to tell us that the rational response to disagreement with an epistemic peer is to reduce our confidence in the contentious proposition. Perhaps this is reasonable, though, I am not sure (it certainly doesn't conform with the usual practice). A deeper problem seems to be that, if this is right, Amy could conceivably be rationally required to stop having any confidence in H whatsoever, if only she were to happen to encounter enough opponents of H. Presumably, whether those you converse with endorse or reject a particular hypothesis is a contingent matter, and it is not obvious why a series of chance encounters should compel Amy to cease thinking that H is probably true.
What do people think? Is evidentialism plausible? Is moderating one's view the rational response to peer disagreement, or is it perfectly rational to remain steadfast in ones belief?
