My Canadian usage matches the description above. "Diapers" when worn, just like pants. "Diaper" when clean and unworn. "Dirty diapers" (plural) after being worn and removed.

I could be wrong, but I'm pretty sure we always used it in the singular. "Change the baby's diaper". "Baby needs his diaper changed". Or maybe the nouning ("baby needs a diaper-change") is confusing me. I have 7 younger siblings, so be sure I've heard these phrases many times.

In German there's no interferents from the word for pants since "Hose" is singular too. But in some context you can use Windel (sg.) and Windeln (pl.) interchangeably, for instance when you say what the baby is wearing.

Maybe it has something to do with the fact that what you usually do with diapers, as an adult, is change them, and that always involves a used diaper and a clean one.

My wife and I consistently used diaper as the singular with our kids (born between 1991 and 1995). The sentence "Alex needs his diaper changed." never used "diapers".

The Language Log discussion of diaper(s) got sidetracked by the author's including "diapers" among pluralia tantum like "trousers" or "pants."

I've never heard "diapers" used as anything but the plural of "diaper." At a single moment, someone is in diapers only when wearing more than one diaper, as for additional absorbency.

Over a period, of course, a diaper-wearer will wear plural diapers. Journalists who reported that the aggrieved astronaut was wearing "diapers" would be correct only if they were referring to her changing from one diaper to another during her journey. Soiled diapers found in a trash bag in her car suggest she did just that.

Never mind the diapers, it's 'Mommy' that made me cringe.

Any preference for the plural diapers probably comes from the fact that there is no end to them, and they just don't exist singly. It's like potato chips -- you can't eat just one potato chip, and you can't use just one diaper, because you'll soon need another one. Whether disposable or reusable, any parent knows that if you only have one diaper you're in trouble.

"If I am like him and mess my trousers the way he dirties his diapers, Mommy will love me again."

It seems to me that the idea of 'regularly' applies to both trousers and diapers and that plurality is implied in both usages so this has nothing to do with 'trousers' as a duality. Also, it does not seem to me that 'diapers' is in the process of becoming a fixed plural usage. I'll only believe that when I see a text which states that he is wearing a "diapers". Otherwise, diaper is singular, diapers-plural or as an imperfective of repetition, as in "Little Johnny is still in diapers."

So is Johnny wearing a trousers or is trousers not a fixed plural usage or is it a pluralias tantums?

Precision of language is another reason for keeping "diaper" as the singular and restricting "diapers" to the plural.

With "diaper" being the only acceptable singular, we can tell from "He's wearing a diaper" that he's now wearing just one. Likewise, from "He's wearing diapers" we know that he's now wearing more than one or that he wears multiple diapers cumulatively.

It'd fog the meaning further if "He's wearing diapers" also could stand for his wearing just one.

If any of you watch television's "Queer Eye for the Straight Guy" you would have heard fashion "expert" Carson Kresley repeatedly say "nice pant" and "flat front pant." He seems to reject the word 'pants.'

Aren't little kids the arbiters of this kind of thing? I recall a conversation that went like this:

ME: "Do you have a poopy diaper?"

Two-year-old girl with overdeveloped clothing sense: "No, it's a poopy Cinderella pull-up."