We have seen that Thomas Reid credits even young children with a solid understanding of promises and the obligations they entail. Recall his example of the two boys playing with a top and scourge. Let's continue this story for Reid. Suppose the top belongs to Calvin, the scourge to Andy. Calvin takes the first turn. When the top stops spinning, Calvin hands the scourge back to Andy, picks up his top and abruptly leaves. “But you promised,” says Andy. Absent some special explanation or apology, both boys should agree that a wrong has been done. Not only is Andy disappointed at not having his turn with the top, seemingly the trust he extended to Calvin was betrayed— Calvin had given his word.

What else needs to be added to this story for us to understand what has happened and why the boys should see it as morally problematic? For Reid, very little, if anything. The mutual promise made by the boys is understood by both to have committed them knowingly and willingly to take turns. But this is likely not the only communication between them. For example, Calvin might also have indicated to Andy that he was going to an event with his parents that evening. But this would not be a promise of anything to Andy. It may suggest that Calvin believes he has an obligation to be with his parents that evening. However, Calvin's departure without offering any explanation parting words need not call this to mind. To all appearances, Calvin simply broke his promise to Andy.

Clearly, Calvin and Andy know how to promise, and they can recognize when a promise has been made to them. They both know that Calvin's breaking his promise without any explanation or indication that he will make up for this later is morally problematic. This story, we could say, presents us with the premise of a promise. This premise does not include a definition of “contract” or “promise.” It does not presume or rely on an underlying, elaborate theory of promising. It includes only the boys’ understanding of what has taken place. Calvin and Andy promised each other and thereby took on obligations to each other.