The principle of noninterference

Imagine Alan sitting on a public beach, a pebble in each hand, splitting one pebble by striking it with the other. Betty, a casual passerby, asks him what he is doing. She can see, of course, that he is splitting pebbles; what she is asking him to do is explain it, to redescribe it as an activity with an intelligible point, something he could have a reason for doing. There is nothing untoward about her question, but Alan is not bound to answer it unless he likes. Suppose, however, that Betty had asked Alan to justify what he was doing or to give an excuse for doing it. Unlike explanations, justifications and excuses presume at least prima facie fault, a charge to be rebutted, and what can be wrong with splitting pebbles on a public beach? Besides, so far as we can tell, Alan is not obliged to account to Betty for his actions. Of course, if Alan were a sentry and Betty his commanding officer, he might indeed be at fault, and she would be entitled to call him to account for neglect of duty. But that is to ascribe special action commitments and liabilities to Alan, and special powers to Betty. Those absent, Alan has no obligation to meet a challenge to justify his performance until there is a charge to answer.