Much of what we take ourselves to know we picked up from others. You know your own date of birth, for example, only on the basis of others’ say so. But people can be capricious or incompetent. It’s imaginable that those from whom you learned your date of birth lied—perhaps, for example, to preserve you from the indignities of celebrating on 29 February or 25 December. And it’s imaginable that they’re mistaken: in the haze of delivery, they missed that you were born just before midnight. Furthermore, you seem to lack decisive evidence, independent of others’ say so, that your sources are sincere and reliable. Perhaps you might check with the hospital. But even hospital staff make mistakes. Nonetheless, for all that your knowing depends on its being right for you to trust other people, you take yourself to know your own date of birth.

Perhaps it’s not terribly important to know one’s own date of birth. But the issue generalizes. You take yourself to know that your children attended school today and that their teachers are qualified. You take yourself to know that the bottle contains milk rather than white paint, and that you paid one pound rather than one hundred pounds for the pleasure of owning it. And then there are all the things that you take yourself to have learned from books, newspapers, or the internet. You might cautiously take yourself to know only things that are reported by at least two independent sources. But how do you know that there were two sources, rather than a single source with two pseudonyms? In all these cases, and in many others, you rely upon others’ say so. Insofar as you know any of these things, your knowing them seems to depend upon your trusting others to be sincere and competent. Can beliefs that are formed on the basis of trust ever amount to knowledge?

The idea that beliefs based on trust rarely, if ever, amount to knowledge seems rampantly sceptical. That is, it seems to entail that we know far less than we would ordinarily take ourselves to know. It might leave standing a core of knowledge about things that you have witnessed for yourself. But even with respect to that core, there is room to worry. You believe that what you can see is a tree. But that belief seems to depend on your trusting those who taught you, or who withhold correction, that things like that are called ‘trees’. And unlike the idea that you might be dreaming or in the Matrix, scepticism about what others have told you seems not to depend on science fiction. Rather, it seems to depend only on things we take to be obvious: people sometimes say things that are false; and when they do, we are often in no position to tell that they have done so.

The worry, then, is this: In cases in which we come to believe something on someone else’s say so, we often have no independent evidence that they are sincere and competent. Our evidence that they are speaking their minds, rather than lying, and that they they are speaking from knowledge, rather than ignorance, seems, at best, to leave the matter open. Because we lack independent evidence as to their trustworthiness, it seems to be up to us whether or not to trust them. But if they are insincere or incompetent, then that would seem to preclude our coming to know by accepting what they tell us. And although we might decide to trust them, doing so without evidence is surely not a way of coming to know that they are trustworthy.

The worry becomes pressing if we assume that what we are presented with by someone who speaks from knowledge can be of just the same kind as what we are presented with by someone who doesn’t speak from knowledge. For we know that people can fail to speak from knowledge, either due to malice or to ignorance. And when they fail to speak from knowledge, accepting what they tell us will not, in general, furnish us with an opportunity to know. So, the capacity of someone’s telling us something to provide us with an opportunity to know seems to depend on something that is absent from that sort of case. Specifically, it seems to depend on whether they speak from knowledge. And now if what we are presented with by someone who speaks from knowledge can be of just the same kind as what we are presented with by someone who doesn’t, then what we are presented with will seem to leave open the question, did they speak from knowledge? There would be a gap between what we are presented with—a telling that is neutral between someone’s speaking from knowledge and someone’s failing to do so—and what must be the case if we are to acquire knowledge—that they speak from knowledge. In that case, traversing the gap would require either evidence that they speak from knowledge, or a leap of faith: trust in the speaker, in the absence of evidence that they are worthy of that trust.

Strictly, what you would lack in that case is knowledge that the speaker speaks from knowledge. And it’s not obvious that lacking that knowledge about the speaker must prevent you from coming to know things by accepting what they tell you. That is, it’s not obvious that knowing what they tell you depends on knowing that they speak from knowledge. Compare this with knowing by sight that a t-shirt on display in a shop is yellow. If the lighting in the shop were abnormal, a white t-shirt might look to you the way that the yellow t-shirt now looks. However, even though you are ignorant about the normality of the lighting, it’s plausible that this needn’t prevent you from knowing by sight, given the actual lighting conditions, that the t-shirt is yellow. Similarly, perhaps what matters to your acquiring knowledge by accepting what someone tells you is just that they in fact speak from knowledge, whether or not you are in a position to know that they do.

If that analogy could be made out, it might help to defend our ability to come to know by accepting what we’re told. But it wouldn’t resolve all difficulties. For the analogy preserves our capacity to know the things we are told only at a cost to our knowing whether we know those things.

Consider again your knowledge that the t-shirt is yellow. Minimal reflection reveals that if you know, going by how the t-shirt looks, that it’s yellow, then the lighting must be normal. But if you know that, and also know that you know, going by its looks, that the t-shirt is yellow, then you seem to be in a position to infer, and so come to know, that the lighting is normal. And yet we assumed that you are not in a position to know that the lighting is normal. Something has gone wrong, and it’s natural to blame the assumption that you know that you know that the t-shirt is yellow.

Similarly, minimal reflection reveals that if you know, from what the speaker tells you, that there’s milk in the fridge, then the speaker must have spoken from knowledge. But if you know that, and know that you know that there’s milk in the fridge, then you seem to be in a position to infer, and so come to know, that the speaker spoke from knowledge. And yet we assumed that you weren’t in a position to know that. Again, it’s natural to blame the assumption that you know that you know that there is milk in the fridge. If that’s right, then the analogy may help to protect knowledge that we acquire from others, but only by leaving us ignorant about whether any of what we accept from others amounts to knowledge.

Perhaps that’s a cost we have to bear. Alternatively, we might reconsider the assumptions that drove us to this point. One assumption was that what we are presented with by someone who speaks from knowledge can be of just the same kind as what we are presented with by someone who doesn’t. The assumption is apt to seem natural, especially given that we often can’t tell when someone fails to speak from knowledge. But it has become increasingly common for philosophers to question the move from the claim that when things go wrong, we can’t tell that they haven’t gone right to the claim that when things go right, we can’t tell that they haven’t gone wrong. There is space here to argue that although we often can’t tell when people don’t speak from knowledge, still we often can tell when people do. But you’ll have to take my word for that.

Image credit: jinterwas, ‘Can you keep a secret?‘