Chris Achstetter writes: "I would like to bring an interesting fact to the attention of your readers. I refer to the uneven enforcement of laws regarding the sale of alcoholic beverages to minors.

"I'm 17, but can go (and have gone) into bars on Capitol Hill and in Bethesda and be served beer, even though I am obviously a member of a small group of nonadults in the establishment.

"I went to a store in Bethesda one night and bought two cans of beer, which I used to break a harmonica. I wasn't asked to produce proof of age. Several weeks ago, also at night, I bought a six-pack of Canadian beer at the same store.

"Several days ago, however, I attempted to buy one can of beer (which seems to be an amount too small to intoxicate someone, which seems to me to be what liquor laws are meant to prevent), but was unable to, for lack of proof of age.

"I'm not indignant or upset at not being able to buy beer, But by the inconsistency of the enforcement of the liquor laws. Why can't the owners of stores and bars be more consistent?"

Chris, you pose a simple question to which there are more answers that I can list here.

For openers, human beings are not consistent because inconsistency is a common human failing. The same person who sells you beer one day may turn you down the next. One day he may think he's too busy to ask for proof of age; the next he may have nothing else to do and become a tiger about enforcing the law. Or it may simply be that his mood is different.

In addition, compliance with the lawy varies from one owner to another, and from one clerk to another. Some have a greater appreciation of the law's social validity than others. Some think one can of beer can't hurt you, others know that the law doesn't give them discretion in selling only one can.

Some owners are more greedy than others. Some have clean records with their ABC boards, others are already in hot water and must take care not to be caught in additional violations. Two owners of equal zeal in complying with the law may have unequal success in persuading their employees to demand proof of age. There are a zillion reasons for inconsistency.

If you ask the police in a specific jurisdiction why liquor laws are not enforced with a heavier hand, you are likely to get a two-pronged response: "We do have good enforcement, and last year we prosecuted x number of violations," plus the classic reply, "We can't put a policeman in every store and bar, and this is not the kind of offense to which we can justify assigning a top priority."

This brings us to the nub of the matter, Chris. The police are right. In the long run, obedience to society's rules depends on voluntary conformity rather than on "enforecement." The burden is upon each of us to conform, not on the police to catch us in violations. Unless a society is permeated by an attitude of voluntary obedience, the only way to achieve that obedience is by assigning a policeman to watch every citizen. We'd have to become a nation of deputy sheriffs.

Inasmuch as voluntary obedience is not exactly universal in our society and we also do not have a policeman watching each citizen, we have inconsistent law enforcement.

If you're 17, this might be a good time for your to decide what kind of adult you're going to be - the kind that says, "Oh, well, everybody else cheats a little, so what the hell?" Or the straight-arrow kind that respects all laws, even the ones with which he disagrees, and plays an active role in trying to get bad laws replaced by good ones.

We already have an ample supply of people in the first category, but could really use some fresh recruits in the second. I strongly recommend that you join the lonely minority - even if it does cause some of your friends to think you're a kook.