Natural law thinkers view the happiness of the community as the complete set of conditions, physical and social, that need to be satisfied in order for individuals to be able to pursue happiness effectively, both through their own actions and through the actions of smaller communities such as families, churches, and neighborhoods.

But wait:  If the common good really is the "universal happiness," then why not think of it in a different way?  Why not think of it the way utilitarians and cost-benefit analysts think of it, as an arithmetic sum of my happiness, your happiness, and everyone else's happiness?  Isn't that what "universal happiness" would mean?

No, because society is not a mega-person.  It is an association of persons, each of them distinct and irreducible.  To the utilitarian and the cost-benefit analyst, persons seem to run together, like oil cans being emptied into a drum, gingerbread men placed too close on the cookie sheet, or lead soldiers melting down in the furnace.  But this is absurd.  To say "Your happiness is -3, mine is -3, and that other fellow's is +5, so the happiness of the aggregate is -1," makes about as much sense as saying "Iowa's temperature is 75°, Wisconsin's is 70°, and Minnesota's is 68°, so the temperature of the tri-state area is 213°."

Every person’s life is bound up with his membership in the community.  I am more than just a solitary atom; I am a part of a whole.  But the individual's identity is not exhausted by his membership in the community.  As Thomas Aquinas explains, the kind of unity that the commonwealth enjoys is not a "unity of essence" or a "unity of matter," but only a "unity of order," amounting to no more than the fact that things stand in a shared relationship.  "To be one in respect of order is not to be one unqualifiedly speaking," he says, "since unity of order is the least of unities."

Consequently, although I am a part of the community, I am not only a part.  A person is not like a hand, which takes its entire identity from the body to which it belongs.  He is a complete being, subsisting of himself, distinct from all else, the ultimate possessor of his properties in the sense that they are predicated of him, not of anything or anyone else.

Even so, his membership in the community matters.  It is not just something that affects him, but something about him.  The fact that I am a part does not imply that I am only a part; but neither does the fact that I am not only a part imply that I am not a part.

Not all common goods are equally common.  In the weak sense, a good is common merely when it is good for everyone, like pure water.   Different people in the community may enjoy different amounts of weakly common goods.  In fact, if one person grabs more of a weakly common good, then other people have less.   For example, I might divert part of the river away from your property and onto mine.

In the strong sense, a good is common when one person's gain is not another's loss, so that our interests literally cannot diverge.   The best examples of strongly common goods are the virtues, the goods of character:  I don’t become less wise, or less just, or less courageous, just because my neighbor becomes more so.

Yet there is a paradox, for although we can’t really be in competition for strongly common goods, we may feel as though we are.  Suppose I envy you for being

wiser than I am.  This is plainly irrational, because the greatness of your wisdom doesn’t leave less wisdom for me; I might even gain wisdom from your teaching and example.

But the envious man does not see it that way.  Even though the greatness of your wisdom does not diminish the absolute amount of my wisdom, it does diminish the relative amount of my wisdom, for the wiser you are, the lower I rank in comparison, especially in the eyes of others.  I may therefore sorrow that we cannot trade places; I might wish that you were less wise, and I were more.

Although we cannot really be in competition for wisdom, we can certainly be in competition for rank, and so, unexpectedly, something that in one sense excludes the very possibility of rivalry in another sense becomes a motive for rivalry.

Perhaps this will amuse no one but me, but I am surprised by how many reviewers are unable to bring themselves to use the correct title of my book What We Can’t Not Know.  They cite it as What We Cannot Not Know.

What explains this funny scruple?  My guess is that they are haunted by the spirits of long-dead schoolteachers who drilled into them that contractions have no place in genteel prose.  That’s prob’ly what happened.

Yesterday I suggested that James Madison’s Constitutional strategy of “pitting ambition against ambition” is like Hamburger Helper.  Just as meat extenders don’t substitute for meat, so his strategy doesn’t substitute for virtue:  It merely helps the little bit we have go a little bit further.  The theory works like this:  A man who is driven by ambition has a strong motive to restrain other ambitious men, because the more power they attain, the less is left over for him.  If he has no virtue at all, he may restrain them by playing dirty.  If if he has just a little virtue, perhaps he will content himself with clean weapons like constitutional checks and balances.  So everyone is restrained by everyone else, and we are all better off.

The underlying theory can be generalized:  Provided that there is some residuum of virtue, sub-virtuous motives can be channeled to keep even greater vices in check, thereby extending virtue’s work.  Here are a few other example:

For capitalism, the sub-virtuous motive is desire for wealth.  If businessmen have no virtue at all, they will seek wealth by defrauding their customers and seeking to obtain monopolies from the government.  But if only they have just a little virtue, they might compete within a framework of laws against fraud and monopoly by lowering the price and improving the product, to the benefit of all.

For the Roman Republic, the sub-virtuous motive was desire for glory.  If the nobility has no virtue, they will seek glory by corrupting the electorate and assassinating their rivals.  But if only they have just a little virtue, they might compete within a framework of shared expectations about what is and isn’t done by performing acts of conspicuous benefit to the commonwealth.

The flaw in the strategy of using vices to counteract even greater vices was recognized by St. Augustine in his great fifth century work City of God Against the Pagans.  Remember, without that little bit of virtue to steer them, men will pursue their sub-virtuous interests in the wrong ways rather than the right ones.  But the more one relies on such interests, the more the reservoir of virtue is drained.  So unless something replenishes this reservoir, the strategy collapses.  (What can replenish it?  Now there is a question for political theorists!)  Augustine thinks this is why the republican love of glory was replaced by the sheer lust for wealth and power, and the republic collapsed.

He who trains dragons to keep wolves under control must reward them with food. Eventually the dragons grow large enough to hunt their own food. At this point they set aside their training and do as they please.