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September 24th, 2006

Evidence and Memory

This is pretty well worked over territory, but I wanted to run through some options for dealing with cases where we forget our evidence.

For convenience, let p, q and r denote the following propositions. We’ll assume these are true, which does involve taking sides in a dispute about just what constitutes a reign. The Charles’s in the propositions are the 17th Century Kings of England and Scotland.

p = Charles II reigned for longer than Charles I.
q = Charles II reigned for 24 years and 243 days, and Charles I reigned for 23 years and 309 days.
r = Fred’s Year 10 history textbook says that q.

As a schoolboy, Fred reads that q in his Year 10 high school history textbook. He subsequently comes to believe, and we’d naturally say know, that q, and quickly infers p. Some years later he forgets r and q, but still believes p. His belief that p is a strictly memorial belief – he hasn’t come to rebelieve p via some lesser method. Perhaps he remembers some other things as well, say that Charles I reigned from 1625 to 1649 and Charles II reigned from 1660 to 1685, but nothing that entails p. Still, he remembers (as we’d ordinarily say) that p.

What exactly should we say about Fred’s knowledge and evidence in this case? I take it that there are four options on the table.

Option One. Since Fred no longer has evidence that p, he does not know that p.

Option Two. Since Fred came to know that p, p became part of his evidence. So p is part of Fred’s knowledge, it is also part of his evidence.

Option Three. Fred knows that p, since he learned that p and has not forgotten it. But since all his evidence that p has been lost to the mists of time, he has no evidence for p.

Option Four. Fred knows that p, since he learned that p and has not forgotten it. Fred’s evidence that p is q, or perhaps that r. The evidence is not accessible, and if Fred came to believe something else supported by q (with no other reason) this could not be knowledge because it was not based in q, but q is still his evidence for p.

I think I prefer Option Three.

Option One seems absurd – since it requires that we remember our evidence if we are to preserve knowledge, and that is too strong.

Option Two seems to make it the case that p is self-evident for Fred, and this seems wrong. Not because it is contingent, or anything of the sort. Nor because it is a proposition about which Fred could be wrong. It is self-evident (to me, now) that there is a computer on the table in front of me. That is, that there is a computer on the table is something I know simply because it is part of my evidence. Perhaps it is self-evident that all men are created equal. (I go back and forth on this.) But it isn’t self-evident that p.

Options Three and Four are both odd, but I think in both cases the oddities can be lived with.

Option Three is odd because it says that we can know something without having any evidence for it. It might seem plausible that knowing things requires that we have evidence for them. But option three is consistent with the only slightly weaker claim that knowing something requires having, or having had, evidence for it. In any case, the possibility of innate knowledge suggests that this principle is a little strong.

Option Four is odd because it says that we have evidence that we can’t use for any purpose. A natural account of what it is to lose evidence is that we had the evidence and no longer have it. And it is very natural to think that when Fred forgot about q, he lost his evidence for p. But if we accept this option, we can’t say both of those things.

I think all things considered I’d prefer Option Three, but Option Four doesn’t look clearly wrong. Options One and Two do, at least to me, look pretty badly wrong. Perhaps though there is another option that I’m forgetting. Any thoughts?

Posted by Brian Weatherson in Uncategorized

6 Comments »

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6 Responses to “Evidence and Memory”

  1. jed says:

    This seems like a case where you believe something because someone you trust told you it is true, but they didn’t tell you their evidence. It’s just that the person you trust was your earlier self.

    Note that you might have classes of prior judgements you don’t trust — so you don’t trust your earlier self unreservedly. But in this case (by hypothesis) you’ve found your schoolboy history conclusions to be reliable, so now you believe what that earlier person tells you, in this domain.

  2. Kent Bach says:

    How about this embellishment of Option Three?

    Option Three+. Fred knows that p, since he learned that p and has not forgotten it. But since all his prior evidence that p has been lost to the mists of time, he has no evidence for p other than the fact that he remembers it (or, if you like, seems to remember it).

    So, for example, ask him what’s the capital of North Dakota and he answers “Bismarck.” How does he know? Because he remembers it. Ask him how he knows, all he can say is: “Because I remember it.”

    Of course, there can be phenomenologically similar cases in which one doesn’t know, either because he misremembers or didn’t know in the first place, but that’s analogous to an old familiar problem about knowledge by perception.

  3. Brian Weatherson says:

    I don’t think it’s right to assimilate memory to testimony from an earlier self. The reason is that failures of the ‘testifier’ have different effects in the two cases. If you believe that p for a bad reason, I rather don’t think you know that p when you later ‘remember’ it. But if someone else tells you that p, and they are reliable in this area, and you know this, then it seems much more plausible to me to say that you come to know that p, even though perhaps they did not know that p. That’s not exactly a conclusive argument, but it’s sufficient for me to not want to run the two cases together.

    Kent is entirely right that I should have said much more about why I wasn’t just taking the memory to be the evidence. Because this is obviously a very attractive option, given the problems with the others. Nevertheless, I don’t particularly like it, for the following reason. (I should say that Kent is right of course to say the fact that this would mean there are cases that are phenomenologically similar where agents have distinct evidence is no objection, since there’s no conclusive argument, to say the least, that evidence supervenes on phenomenology.)

    Question: In such a case, is Fred’s evidence p or his memory that p? If it is the first, then the objections to Option Two come back. But if it is the second, we have a rather odd state of affairs. I’d say the memory that p just is the belief that p, so if it also justifies the belief that p, then the belief is self-justifying, which seems odd.

    As I briefly mentioned in the post, I like thinking of evidence as consisting of propositions like q (in this example) rather than r. One reason for that is just that it seems psychologically more realistic – I make inferences from things in the world, not from my mental states. A stronger reason (at least to me) is that it means evidence can be shared, and it is a platitude that people can have the same evidence.

    Now if the evidence in the first place consists of propositions about the external world, like q, rather than propositions about the subject’s relationship to the world, like r, then it would be an odd asymmetry for propositions about the subject’s memory to be evidence. So that’s another reason I don’t like taking propositions about the subject’s memory to be evidence.

  4. Geoff says:

    I’m not sure whether Fred still knows p. But it does seem to me that he has evidence for p, which is that he believes that he remembers that p, or that it seems to him that he remembers that p, or something like that. Sure, such evidence is pretty second-class, but those propositions could serve as perfectly good premises in an ampliative argument for p. (What explains the fact that Fred has this belief? Well, probably it’s because he does remember that p. And if that’s true, then p is true.) Plus, Fred knows them. Also, this evidence can be shared; all Fred has to do is tell somebody about his beliefs or seemings and they become evidence for her that p as well.

    If you don’t want to say that propositions about a subject’s beliefs are among his evidence, then obviously you won’t want to say this, but I’m not sure I understand the motivation for excluding “propositions about the subject’s relationship to the world” from his evidence.

  5. dbradley says:

    Let’s go with the second horn of Brian’s dilemma. Say that Fred’s evidence is his memory that p, and that this is just a belief that p. The threat is that p is self-justifying.
    But what about if we added certain information about how memories are formed? Suppose I know that I had a reliable belief-forming mechanism. Then any memories I have will have been formed in a reliable manner. If I find myself remembering that p, I can infer that something in the world must have made me believe that p in the past. It seems that the conjunction of my memory that p plus my beliefs about the reliability of my memories, will suffice to justify me believing p. So p is not self-justifying. But we get justification if we add beliefs about reliable past belief-forming mechanisms.

  6. Ken Taylor says:

    Here’s a variation on your case Brian that has to do not with knowledge but simplyh with reasons to believe, admittedly short of knowledge.

    Suppose that I find myself believing that p. But have lost track of my reasons for believing that p. It’s not that I remember that p or even believe that I remember that p. I just find myself believing p.

    But I do think to myself something like the following: I’m a rational believer in the sense that typically I don’t believe that p on the basis of no reason whatsoever.

    Suppose this is true of me and suppose, moreover, that I know that it is true. I now seem entitle to conclude that in the present case I probably [once] had a reason for believing that p. Even though I don’t remember that p and don’t believe that I remember that p.

    So now it does look as though merely believing that p and knowing that I’m in general a rational believer gives me at least a pro tanto reason for believing that p.

    Doesn’t this make the belief that p “self-rationalizing.”

    Would it be so bad if it did?

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