What is it to forget that p? A simple analysis is that S forgets that p iff at one time S knows that p, and at a later time, S does not know that p. But this can’t be right, for the following four reasons.

If at t1, S knows that p, and at t2, S is dead, so knows nothing, S has not forgotten that p.

At t1, George knows that he has hands. At t2, he reads the Meditations, and starts to doubt that he has hands. That is, he no longer believes he has hands. He doesn’t any more know that he has hands, but nor has he forgotten that he has hands.

At t1, John knows that the New Deal substantially lowered unemployment. At t2, John reads a newspaper column, in a usually reliable newspaper, saying that this was not true. With his new evidence, he now (quite reasonably) doubts that the New Deal substantially lowered unemployment. So he does not know this. But nor has he forgotten it.

At t1, Paul knows that his meeting is scheduled for 2pm. At t2, he gets an email (falsely) saying that the meeting has been moved to 3pm. Paul glances at the email, but doesn’t take in what it says. So he still believes that the meeting is at 2pm. Nevertheless, he doesn’t know this, for the email is a defeater for his knowledge. But nor has he forgotten the time of the meeting.

That seems to dispose of the simple theory fairly conclusively. But is there anything we can put in its place?

27 Replies to “Forgetting”

  1. I think we call it forgetting when we feel we should have known p, but now we do not.

    If you are dead, you shouldn’t know anything, so this isn’t a problem.

    For the cases in which a person learns something that makes him or her doubt what they know, then we don’t feel that they should have known p and hence aren’t forgetting.

    There might be a problem distinguishing simple inference from memory, though. But, the more I think about this, the more ornery this problem seems to get:

    I leave my keys on the table. Now I can’t find my keys. Have I forgotten that my keys are on the table or have I failed to make the inference that by leaving my keys on the table and that keys do not move on their own, that they are still on the table?

    oh well….

  2. S forgets that P just in case:

    (i) S exists at t1 and t2,
    (ii) S knows that P at t1,
    (iii) S does not know that P at t2,
    (iv) S does not know that P at t2 precisely because S stopped believing P through some nonrational process.

    Also, I should mention that sometimes we’re willing to say that we “forgot” something if we don’t consciously recall it, even though we still believe it. This seems like an importantly different type of forgetting, though, which might be better labeled “failure to recall.”

  3. John,

    Your proposal seems to be too broad. One can stop believing that p through some non-rational process without forgetting that p. I stop believing it’s really cold outside today (and believe me it is) because I’d like the weather to be warm, my belief-changing process seem to be non-rational but that does not seem to be a case of forgetting that p.


    I’d be tempted to say that forgetting cannot be analyzed in purely epistemological terms but needs to be analyzed in partly psychological/cognitive ones (ok I know I’m opening a big can of worms here). One for example could borrow the (I take it cognitive) notion of a belief-sustaining process as it is sometimes used by reliabilists and claim that one forgets that p when the belief-sustaining process that used to saustain one’e belief that p ceases to operate. (A more general way to put the point I made above may be that an analysis of forgetting is to be carried out in terms of causes of beliefs not of reasons for beliefs.)

  4. My first thought is that – as with remembering – we need the concept of a memory-trace to explain forgetting. A first go:

    S forgets that p iff – at one time S knows that p, and at a later time, S does not know that p; and – the cause of the later not knowing is the loss of a memory-trace recording p.

    The difficulties with that look like being (1) filling out ‘loss’ appropriately: destruction? mutation? inability to access? And (2) describing the ‘recording’ or representation involved in being a memory-trace for p.

    But is there a general reason not to go this route? It seems pretty successful for remembering.

  5. What about the following modification of John’s condition(iv): S does not know that P at t2 because S stopped believing P through some nonrational and nondoxastic process.
    This appears to exclude wishful thinking. However, I’m not sure if it also excludes various forms of brain damage, some of which might not be intuitive cases of forgetting.

  6. I think Gabriele is probably right that we won’t be able to have a purely epistemic theory of forgetting. Something about how the agent came to cease to believe that p will probably matter.

    Two other quick thoughts.

    I don’t think we can cash out forgetting in terms of things we should still know. I used to know the names of all the members of Geelong’s 1989 Grand Final team; now I don’t. I’ve forgotten some of them. But there’s no reason I should still know this. It was relatively trivial information; it was a long time ago; and in any case, they lost.

    I also think that some kinds of brain damage are forgettings. Some people who suffer serious brain injuries forget their own name. But maybe that’s a sloppy use of language.

  7. That’s probably a bad phrase, isn’t it?!

    I was thinking that a theory purely in terms of things like evidence, reasons, justification and the like would not carve the cases in the right way. Something else, something about the metaphysics of the belief as it was at t1, and about how it ceased to be before t2, would have to be brought in.

  8. Jonathan and Gabriel,

    In both of your cases, I’d say the process is irrational, but not non-rational. Non-rational processes would include losing the belief because of a head injury or the gradual loss of neurons that previously underwrote the relevant mental state.


    “There were some comments in moderation while I was off teaching. Now I’m back and the comments are approved!”

    Please get your priorities straight. 😉

  9. I’ve always assumed that forgetting involved the degradation of a data structure that represents a memory content within a more or less stable representational substrate (e.g. mind/brain) or at least the (possibly temporary) loss of access to said data structure while conscious. This covers not just dying but results of massive damage, which we may not want to call forgetting (not all memory loss is forgetting imho).

    You might want to say something special about switching cases if you think that switching cuts off access to your original memory contents. Hmmm, uh oh, I think I’m on record as saying that somewhere.

  10. Jonathan (and Brian),

    I knew that distinction was going to get me in trouble (btw, I should have probably ‘distinctively epistemological’ rather than ‘purely epistmeological’ but, since Brian (and I assume others) got what I meant, I guess the label served its purpose), but, by and large, I stand by the distinction. One can give of an account of the causes of someone’s beliefs that is couched in a purely descriptive vocabulary and epistemologists typically use a large chunk of that descriptive vocabulary. However, epistemologists use also a vocabulary that is intended to give an account of someone’s reasons for holding a certain belief and for evaluating those reasons. It is this second prescriptive or normative vocabulary that I consider distincitvely epistemological. My suggestion was that forgetting does not seem to be necessarily a phenomenon that needs to be handles in distincitvely epistmological terms.


    I was assuming your ‘non-rational’ included ‘irrational’, but now I see that what you were proposing is not too far from what I was saying—something along the lines of forgetting that p is to abandon the belief that p for something that is not a reason (so that it is neither a good nor a bad reason).
    (I wrote this really quickly so I hope it makes sense! Sorry if it doesn’t. I’d be happy to expand if anybody wants me to).

  11. I’m not convinced by the wishful thinking examples. Even if it’s wishful thinking that causes me to go out at night without a jacket, doesn’t it also sound right to say that I forgot that the temperature in California changes greatly after dark?

    Also, in some cases of forgetting it seems that one may still count as believing (and even knowing) the relevant proposition, but one counts as forgetting it because it’s not in the stock of propositions that one actively entertains, or would entertain if asked to think about relevant things. For instance, I might count as forgetting that I teach on Wednesday afternoon if I don’t think of my class when asked about anything I might be doing on Wednesday afternoon, even though I can answer immediately and correctly when asked when my class is, and therefore seem to count as believing and knowing it.

  12. Gabriele, is ‘belief’ an epistemic property? I would have thought so. But I also hope that our ultimate cognitive science can make sense of it.

    Is it distinctively normative? I’m inclined to think it is, but I expect many will think it’s not.

    I agree with you that any true account of forgetting will have to invoke considerations about, for example, the cognitive processes that led up to the doxastic state in question. But then again, I think the same thing about knowledge.

  13. After Sam C, how about this? S has forgotten that p if S once knew that p and S now does not know that p because S does not remember that p.

    There’s some complications in there about “cause”; if I lose the belief that p through wishful thinking or even through acquiring new misleading evidence, I no longer remember that p; in these cases does my no longer remembering that p cause my not now knowing that p? It seems to me that it doesn’t, but I don’t do enough work on causation to be able to say that confidently, and I don’t think that the analysis of forgetting should be hostage to the analysis of cause. Maybe it would work to say: If used to know that p and now do not, there was an event of your ceasing to know that p; if the cause (the main cause?) of that event was that you failed to remember that p, then you have forgotten that p. Though it also seems to me in general wrong to say that ceasing to know happens at an instant.

    This also requires analysis of remembering, but I think our analysis of forgetting should be inextricable from our analysis of remembering, so that’s OK.

  14. Jonathan,

    Of course, I don’t mean to deny that the notion of belief is a central notion in epistemology and I have no problems with calling it an epistemological notion but I don’t think that this alone makes it distinctively epistemological (btw, I’m not sure in what sense you think ‘belief’ is a normative notion, could you expand a bit on that?).
    This is the (admittedly simplistic) story that I usually tell my students on the first day of an epistemology class when explaining the JTB analysis of knowledge. If they want to find out more about epistemic justification (and knowledge) then they are taking the right class, but, if they want to find out more about what is for S to believe that p or for p to be true, then they’d better take, respectively, a philosophy of mind course and a metaphysics course (or maybe philosophy of logic course?). So, the simplest (and most simplistic) way to put the point I was trying to make is probably that, insofar as epistemology is concerned with changes in someone’s doxastic state, it is concerned with those changes to doxastic states that that are subject to evaluation in epistemically normative terms (or if you want with the reasons not the causes of the change) and, as far as I can see, forgetting doesn’t seem to be one of those changes because it is a change that occurs for a cause that is not a reason. (My intuition is that, whereas we might take one to be legally or morally responsible for forgetting that p in some cases, we wouldn’t take them to be epistemically responsible.)

  15. Ludlow seems to me to have got it right except that we would then need to define “mind”.

    If I had a state of mind and then experienced this state of mind at another time with an accompanying new component of the state that indicates “I remember this” then I have remembered the previous state. If I do not have a state of remembering a previous state when challenged at a particular time then I have forgotten it at that time.

    This would seem to minimise the number of undefined components in the problem so that only “mind” is mysterious. In the other analyses above we have “belief”, “knowledge”, “cause”, “memory trace” as mysterious, difficult to define entities.

    I would guess that this proliferation of entities is due to an acceptance of irrational arguments against the existence of mind. See Blind Willie Johnson’s thoughts on this matter.

  16. Gabriele,

    I’m sort of in this Williamson camp that belief constitutively aims at knowledge; it’s therefore ultimately normative. In terms Williamson wouldn’t agree with: it’s analytic that non-knowledge belief is defective.

    For not-unrelated reasons, I don’t see that it’s helpful to try to regiment out, for example, belief, in non-epistemic terms. (But I don’t object to oversimplifications for introductory students; I see the value in teaching the way you suggest.)

    I know there’s this tradition that the non-belief states that are relevant to epistemology (e.g. perceptual seemings) aren’t rationally evaluable; but I’ve never found it compelling. There are good and bad ways for lower-level visual processing systems to generate seemings, just as there are for higher-level cognitive ones to generate beliefs. I don’t see why the epistemologist can’t consider all of these valuations.

  17. About memory traces and similar analyses: I think we want to allow for cases in which we forget something for a moment. (There are plenty of Google hits for the phrase “I forgot for a moment,” and lots of them are forgettings that p.) In such cases the memory-trace clearly isn’t completely lost, or you would forget for more than a moment. Maybe this cases are covered by Sam’s and Peter Ludlow’s comments about loss of access; but I wonder, is anything gained by saying “perhaps temporary loss of access to a memory-trace/data structure” instead of “failure to remember”?

  18. It’s definitely true that sometimes we do want to say that we still knew (or believed? and consequently believed?) something even though we’d forgotten it for the moment. So you have a good point there. And in general I like the structure of the analysis; I just think it might be better to make (iv) depend explicitly on the memory. Part of this will depend on how we can flesh out the non-rational/irrational distinction.

    But it’s still not clear to me that most cases of forgetting will be in line with the “loss of memory trace” examples; there can be cases where I forget something for a whole day, and even affirm the opposite, before I remember and say, “Oh yes, I did lock the door behind me; I remember doing it now.” We wouldn’t say that, when I was protesting that I didn’t lock the door, I believed that I had. But the memory trace was still there; perhaps buried a bit deeper than in the “forgot for a moment” cases, but it doesn’t seem to me that it’s a difference of degree.

    I also think, pace Gabriele, that we’re going to need to look more closely at the concept of belief if we’re going to try to regiment cases according to whether you still believe something but can’t consciously recall it; these cases seem to me like cases in which you believe it in one sense but not another.

  19. I wouldn’t assume that one doesn’t know things one has forgotten. In a paper in draft I offer the following example:

    Ben reads an email saying the bridge he normally crosses while driving to work will be closed and he infers that he will have to take a different route tomorrow. Tomorrow arrives and he heads toward the closed bridge, failing to remember that it was closed. He arrives at the closed bridge, slaps himself on the forehead and says “I knew the bridge was closed”. Or alternatively he says “I forgot the bridge was closed”. Both seem true. One issue is the temporal reference of the “knew” in this attribution. Did he only mean that he knew it when he read the email, or does he mean that he really knew it all along? I’m inclined to think the latter.

  20. Sorry to be a bit late to the party here.

    I’m surprised that nobody has mentioned the logic of belief revision. It would seem to me that to forget a statement (that you previously believed) is to have your belief set contracted by it. When you lose a belief by learning something else (e.g. reading the newspaper) you are revising your belief set with new information.

    Cases of forgetting are usually dissimilar to cases of learning the negation because to forget something is not to proclaim false what one once believed true, but to proclaim indetermined what one once believed true. When it is Tuesday, people who forget what day it is have not “learned” that it is not Tuesday but come to have less credence that it is Tuesday.

    I also think that as forgetting is an irrational process that afterwards our belief set may not be coherently closed under logical consequence. For example at t1 I may believe the following:

    If A then (B and C)
    B and C

    I then forget B, i.e. I come to have no opinion about B. Now I should ordinarily come to believe that (given C) if B then A. As A depends on the truth of B and C, and I have come to doubt B, I should assert that If B then A. But probably because I irrationally forgot B I may come to still believe fully in A. Not realising that I have forgotten B means that I don’t realise I have lost a supporting foundation for A, so I continue to believe it.

    I don’t think the failure to close your belief set deductively is necessary for forgetting, but it is a common addition. I suppose that if a computer or perfectly rational being forgot something it would affect the rest of its belief set.

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