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°."