I was trying to decide whether to put an apostrophe at the end of "couples" in this sentence:
You're invited to the annual married couples breakfast.
My knee-jerk answer is yes, it needs an apostrophe. But then I got to thinking about contrary examples, similarly structured. I wouldn't, for instance, put an apostrophe after "clothes" in this example:
Your coat is upstairs in the winter clothes closet.
My overall question: Why does the first example seem to work well with that apostrophe (though I can see it going either way) while the second seems absolutely correct without it? I can't work out the structural difference between the two examples.