1. Our chief means of encouraging community adherence to a given standard of conduct are to condition some privilege upon compliance with it and to condition some disadvantage upon violation of it. Sometimes we will expressly forbid or reward certain acts. But where we do not propose to do this, we may still create a legal institution to which all persons meeting a certain definition belong. We will then confer privileges upon its members, on the assumption that they will abide by the standard appropriate to the category.
We will not wish to draw the category arbitrarily, lest we undermine the logic of the law by including persons for whom the standard of conduct makes no sense. What counts as arbitrary, however, differs structurally between cases in which we forbid or reward specific acts, and those in which we confer privileges upon members of an institution. In the former cases, it of course matters whether the individual punished or rewarded has actually committed the relevant act. But in the latter cases, we need only ensure that, for every person falling under the definition, adherence to the standard is intelligible, since we have already decided not to regulate conduct person by person and choice by choice.
Within these latter cases, there is a further distinction as to what is arbitrary. If we are conscripting people into the institution, so to speak, it will be important to conscript no one for whom the standard is not intelligible as a default, for it would be arbitrary to draw in persons whose adherence to the standard cannot, prima facie, be assumed. If, on the other hand, people present themselves for inclusion, it matters only that adherence to the standard be an intelligible option, for the very request for inclusion signals that they have chosen the option.
2. In creating such institutions, the law has already concerned itself with the subjective dimension of decision-making. That is, it no longer casts a retrospective eye upon the history of action, but rather has taken into account the entire complex of reasons, motivations, passions, etc. that will lead people to act in a certain way. So there is no question, at this point, of ruling “the subjective” out of bounds as unknowable. (Agnosticism about such things reflects a naïve Cartesianism, by the way, and is out of place among Thomists. Or so it seems to the writer, who admittedly is neither a Cartesian nor a Thomist.)
3. The landscape of human knowledge, choice, and action is not fixed, and neither will be the standards we ought to endorse and the institutions we ought to create. It is possible that the changing landscape will cause legal institutions that were once well defined to become too broad or too narrow—or, in the case of a complex and multifaceted institution, perhaps a little of both. What is called for in such cases is not a rejection of the institution, but a revision that integrates what is right in the old standard with what is right in the new one.
4. Equal treatment is both a legislative and a judicial matter, and it is important to apply the appropriate remedy to a given case. If the laws are being unequally enforced, call in the courts. If a changing landscape has made existing laws arbitrary, let the people change them.
5. Sociology and tradition play no role in justifying the appropriateness or inappropriateness of a standard to a given group of people. They are distillates of historical judgments: ises, not oughts. This is not to deny altogether their value: At their best, they are highly useful indicators of oughts. At their worst, though, they are misleading — since it is possible for large groups of people, particularly marginalized people, to act contrary to their own interests — and can serve as no more than the foundation of an ad hominem fallacy.