Professor Alexander is a provocateur, which is altogether a good thing. And today, in giving us a capsule version of a problem he has thought about for a very long time, (1) he has not failed to provoke.
I, on the other hand, am coming to this problem for the first time, and my tentative reply to his very interesting remarks is that the "gap" of which he speaks is more starkly a problem in theory than it may prove to be in practice. It is an explanatory prism, yes--but an intractable problem? Maybe not.
"The gap" is this with respect to first-order moral reasoning: the difference between what the law requires and what you think you should do. As Alexander puts it, "rules ... will prescribe conduct that some first-order practical reasoning rejects." (2) If they agree, the law is unnecessary, as we would do as it bids without its bidding. If they disagree, no good reason can be adduced to do as law bids, and so law fails.
Professor Alexander considers and rejects various possibilities for closing the gap. I am not quite convinced by each of his rejections. For example, when he speaks of "rule violators who the judges know acted on their first-order practical reasons and for that reason do not deserve punishment," (3) I know of no reason to accept--without more--the conclusion that a rule violator acting on a conviction that a rule is wrong does not deserve punishment.
Be that as it may, what seems insoluble in theory is something we muddle through for the most part successfully in practice. Professor Alexander himself admits that some strategies "narrow but do not close the gap" and taken together they may narrow it considerably. (4) As much as his paradox may trouble us, nonetheless we may observe that most people are lawabiding most of the time, that the instances in which they are scofflaws (for example, jaywalking) are of little consequence, and that the great clashes between the law and the truly conscientious moral reasoner are not high-frequency phenomena.
Moreover, his stark statement of the gap strips away some potentially important nuances. Is the law's command to us that we violate what we hold to be exceptionless prohibitions? This, thankfully, will be rare. Is the law's command that we fulfill a legal duty that is, for us, a matter of moral indifference? This is far more usual. And in all the space between that and the command to do a wrong our morality prohibits, there is a wide zone of greater and lesser conflicts.