According to some, telling is a lot like promising. More specifically, some people hold that in telling and promising one puts others in a position to rely on that which one tells or promises to do by providing them with an assurance or guarantee: in the case of telling, one provides an assurance or guarantee of fact; in the case of promising, one provides an assurance or guarantee that one will act.
We might reasonably wonder at the added value of the assurance. In the case of promising, it would be natural to trace this added value to one’s preparedness to act. On that view, the added value would be conditional on one’s continued preparedness to act. Thus, the value of the assurance would lapse—except perhaps as a ground for complaint—should the preparedness lapse, for example if one shed one’s preparedness or ceased to be. What about the added value of telling?
Were we to press the analogy, we might naturally expect the value also to consist in a preparedness, but preparedness for what? Presumably, not a preparedness to make so what one told someone to be so. Alternatively, then, perhaps the value consists in a preparedness to answer challenges. I tell you that such and such. Were you to tell someone else such and such, they might reasonably challenge your credentials. Assuming that I hadn’t told you anything about my credentials—for example, anything about how I know that such and such—the best you could do would be to tell the interrogator that you heard such and such from me. The added value might be supposed to emerge, then, from my preparedness to take on the obligation of meeting the further challenge: “Well, how does he know?” If we thought that meeting such challenges were in general important, we might then think it of value to you that I offer the assurance that I’m prepared to shoulder the burden. We might even think that, absent my preparedness, you couldn’t have acquired from me knowledge that such and such. For lacking an autonomous full answer to challenges to your credentials, we might hold that you failed to meet a necessary condition on autonomous knowing.
There are three sorts of cases that cause trouble for that last thought. The first sort comprises cases in which you forget from whom you heard that such and such. Having forgotten, you are no longer in a position to exploit my assurance and transfer challenges to your credentials back to me. But your forgetting from whom you heard that such and such would not ordinarily be thought to undermine your claim to know that such and such. (It might do in special cases in which what one knew concerned the teller.)
The second sort comprises cases in which you remember who told you that such and such, but they teller is no longer prepared to shoulder the burden of explaining their credentials. Again, such reticence on the tellers part would seem not to threaten your title as knower.
The third sort comprises cases in which you remember who told you that such and such, but they are no longer capable of shouldering the burden, for example because they have forgotten what they knew, or their credentials, or because they are no longer alive. Again, their incapacity seems to leave intact your knowledge. Moreover, denying that it leaves your knowledge intact would dramatically reduce the extent of your knowledge.
There might be other ways of articulating the analogy between telling and promising, but I suggest that the way considered here is not viable.