Here's how Kinsley's latest Slate essay starts:

Admission to a prestige institution like the University of Michigan or its law school is what computer types call a "binary" decision. It's yes or no. You're in, or you're out. There is no partial or halfway admission. The effect of any factor in that decision is also binary. It either changes the result or it doesn't. It makes all the difference, or it makes none at all. Those are the only possibilities.

For any individual, the process of turning factors into that yes-or-no decision doesn't matter. Any factor that changes the result has the same impact as if it were an absolute quota of one. It gets you in, or it keeps you out. And this is either right or it is wrong. The process of turning factors into a result doesn't matter here, either. In this sense, the moral question is binary, too.

Now, while I actually agree with Kinsley that "O'Connor's opinion... sinks back into a vat of fudge," the logic he uses above is incorrect.

Let's ignore the concept of the wait-list and grant Kinsley's point that admission is a binary decision. His next logical leap to assert that each factor has a binary quality because, "it either changes the result or it doesn't. It makes all the difference, or it makes none at all."

What Kinsley is describing is a necessary and sufficient condition: if X, then Y, if not X, then not Y. However, many admissions criteria are necessary but not sufficient. For example, it's safe to say that you cannot get into a good law school with a felony record. Not having a felony record is a necessary condition, but it does not make "all the difference"; it's not sufficient.

Other admissions criteria are sufficient but not necessary. For example, if an applicant had a letter of recommendation from William Rehnquist saying "this is the brightest undergraduate I've met," that person will be accepted. However, it's not necessary to have such a letter to be accepted.

One can parse conditions further. There are SUNI conditions -- sufficient but unnecessary parts of a necessary but insufficient condition. There are also INUS conditions -- insufficient but necessary parts of an unnecessary but sufficient condition.

Race, in the Michigan admissions criteria, is a INUS condition. To be let in for reasons of diversity, it's necessary for the person to be a minority. There are other criteria that must be satisfied -- no felonies, remember. Race, in and of itself, is not a necessary and sufficient condition.

[Er, does this actually matter?--ed. Let me ruminate on that. I'll update this post if it does. The abuse of logic bugged me, however.]

UPDATE: The abuse of logic bugged Kieran Healy in exactly the same way.