Apostrophes can be tricksters, and one of the trickier uses of them is possession versus description. According to some sources, including the AP Style Guide, some nouns merely describe the noun that comes after them. For example:
The boys team. According to AP style, “boys” describes the word “team,” but the boys don’t necessarily possess the team.
But…but…didn’t you just tell me that I need to use an apostrophe in a sentence like that?
In some, yes. For example: The penguin’s glasses. This is clearly possessive. The glasses belong to the penguin. Even AP would agree with this. But here are two examples from the Columbia Journalism Review’s post about AP’s apostrophe preferences:
A teachers union. Apparently, the teachers don’t possess the union, they just describe the type of union.
A writers guide. Same thing here. The writers don’t possess the guide, but it’s important to know that it’s a guide for writers.
Now, let’s bring things to a whole new level of bewilderment: The Chicago Manual of Style’s apostrophe preferences. Everything I just said about AP? Pretty much the opposite. Chicago favors apostrophes for possession and description. For example:
Consumers’ group. AP would have kicked that apostrophe into next week.
Employees’ cafeteria. AP would have swallowed and choked on that apostrophe just to spite it.
Penguin’s glasses. Here’s that rare circumstance where the two styles agree.
Of course if you don’t need to stick to any particular style, it’s really up to you. If it were up to me, I’d tell the AP’s apostrophe usage to go possess itself. I like my apostrophes, even if they seem superfluous.
Ready to link several apostrophes into a chain and strangle yourself in a punctuation-induced fit of rage? See my post on basic apostrophe use.