Two of the longest sections in most grammar and style guides concern how to form plurals and how to form possessives. Some guidelines are identical—almost no plurals are formed with apostrophes, no matter how many "All Drink's Half Price" signs you see—and some disagree: Is the possessive form of "Texas" rendered as "Texas'" or "Texas's"?

When you put plurals and possessives together, or have more than one possessive, however, you know it ain't going to be easy.

One article said: "In President Obama's and Romneys' cases, fathers — present or absent — are a large part of that cloth." Another referred to "Romney and Obama's biographies. A third talked of "Romney's and Obama's race to November."

Let's first deal with one old possessive "rule." Many people learned that a rendering like "an aide of Romney's" is incorrect. "An aide of" is one possessive, this argument goes (you could say "Romney's aide"), so adding another possessive ("Romney's") makes for a double possessive, a no-no. The Associated Press Stylebook says a double possessive is OK if 1) the second possessive is animate ("He is a friend of John's") AND 2) "The word before of must involve only a portion of the animate object's possessions." ("The friends of John's" is not OK.) And, The AP says, a double possessive is not OK if the second possessive is inanimate ("a friend of the college," not "a friend of the college's"). Got that?

It makes some sense, since you would be more likely to use a simple pronoun instead of a possessive one with the college and say you were "a friend of it" rather than "a friend of its"), but it is a hair split too far. After all, you would say "the college is a friend of mine," not "a friend of me,"so why the unequal treatment?

Of course, you can usually avoid the issue entirely and work around any objection—instead of "a friend of the college" or "a friend of the college's," just say "the college's friend.")

The New York Times Guide to Style and Usage, while advising that the "double possessive" is correct, also says to look both ways before doubling, pointing out "the difference between a picture of Matisse and a picture of Matisse's.

But let's get back to the Romney's and Obama's examples.

When there are two possessives together, but only one "possession," you have to know whether the possession is singular or plural, and whether it is individually and jointly "possessed." That will tell you how many possessives to use.

"President Obama's and Romney's cases" involves a plural possession—"cases"—but Obama and Romney each have at least one. They are individually "possessed," so each of them gets his own possessive: That rendering is correct. In the second example, each has a separate biography, so it should be "Romney's and Obama's biographies." However, the "race to November" is jointly "possessed," so it should be "Romney and Obama's race to November."

Don't get possessed by the "logic" that equal time requires equal apostrophes. That's politics, not grammar.