It seems to be standard to say that a sincere promise requires an intention to do the promised action. However, I doubt this is true. Here's the argument:
- It is sufficient for the sincerity of one's promise to do A that one knows that one will fulfill one's promise by doing A and that one does not intend not to do A or not to fulfill one's promise.
- It is possible to make a promise to do A while knowing that one will fulfill one's promise by doing A, without intending to do A or to fulfill one's promise or to not do A or to not fulfill one's promise.
- Therefore, it is possible to make a sincere promise without intending to do what one has promised.
If this is right, then we need an explanation for why it is usually thought that a sincere promise involves, or even expresses (thus Searle), an intention to do the promised action. One explanation is that typically the intention to do the promised action helps to fulfill one's duty to do the promised action, and sincerity requires that one already be doing (within reason) whatever contributes to the fulfillment of the promise.
In premise (1), I deliberately phrased the condition strongly: one knows not just that one will do A but that one will fulfill one's promise by doing A. It is not enough for the sincerity of a promise that one knows one will do A. For instance, I would be insincere if I promised to have breakfast tomorrow if I also knew that an alien in five minutes would wipe all memory of the promise from my mind, even if I nonetheless knew that I would eat breakfast tomorrow.
One way to argue for (1) is that, except perhaps in really exceptional circumstances, it is the virtue of integrity requires that one only make sincere promises. But the virtue of integrity as exercised in the making of a promise is fully satisfied in respect of sincerity when one knows that one will fulfill the promise, and has no contrary intention.
I think (2) is easy to argue for, too. Just suppose that I am the sort of person who knows himself to always keep his promises. I then promise to do something for you, but I don't care at all about the action promised. Perhaps you agreed to do B if and only if I promised to do A. In that case, my intention is to promise to do A, but not to actually do A. Nonetheless, I know that I will fulfill the promise. But foreknowledge is not intention.
Here is another argument. The sincerity of a promise does not require an antecedent intention to do the promised action. At most what I antecedently need is an intention to do the promised action if I succeed in making the promise, and of course to make the promise, I need an intention to make the promise. (If I accidentally say "I promise", I haven't promised.) Again, take a case where I have no desire to do A, but in exchange for my sincere promise to do A tomorrow you offer to do B today. I thus promise to do A with an antecedent intention to do A if and only if I succeed in promising. For instance, I might have no intention to do A should I start coughing horrible mid-promise and be unable to finish promising. For in that case you're not going to do B for me, as far as I know. So even if an intention is needed, all it needs to be is a conditional intention.
Perhaps, though, we can still say that the promise expresses this conditional intention. But why? An honest person might very well always have a background conditional intention to do whatever she promises. Taking for granted the speaker's honesty, there is no need to express the intention to do A should the promise to do A come off. And if the speaker's honesty is not to be taken for granted, the expression of the conditional is pointless, since saying "I am honest" is of little value.