In his latest column, he agrees with Gail Sepúlveda of Monterrey, Mexico that the following are partitive genitives:
a pair of pantsReally? A partitive construction is one in which there is a part to whole relationship, as in some of the people. In this example, there is a set of people and some identifies a subset of those people (i.e., one part of the group). The same thing applies to non-count nouns, for example a little of the wine.
a cup of coffee
But that's not the relationship in either of the above phrases. Consider the difference between a pair of the pants and a pair of pants. The first is partitive, the second non-partitive. The same applies to the cup of coffee example.
To be honest, I'd never paid any attention to the term partitive though I know I've seen it a number of times before. Yesterday, I wouldn't have been able to tell one from a flux capacitor. But it just takes a few minutes' effort to find out. Unfortunately, too many of us English language teachers seem to lack the curiosity or wherewithal to identify and use good references.