English grammar and such: On the Nature of Bookshelfs

[Carol]

Geoff:
> I think the point is that, in this instance, "Bookshelf" is
functioning as an adjective to "Shelf" or "shelves" and since
adjectives are no longer inflected in English, "Bookshelf speakers"
would be the correct form.

Carol responds:

I agree. However, I suspect that "bookshelfs" (an invented regular
plural for the adjective transformed into a noun) also provides a
useful distinction between bookshelf speakers and bookshelves in a
request addressed to a clerk at Office Depot or a similar store that
might sell both. ("Bookshelves" is, of course, an irregular plural.)

Speaking of which, does anyone know the correct (or accepted) plural
for "mouse" (computer mouse)? Is it "mice" or "mouses" or something else?

Geoff: 
> Other peculiarities which sometimes arise and are wrongly handled in
English 

Carol:
Sorry to interrupt, but I see that you're advocating correctness, not
whatever the masses decide to write or say. Good for you!

Geoff resumed:
are words which are hyphenated or have the noun at the beginning.
Examples which spring immediately to mind are: aide-de-camp, aide-
memoire, master-at-arms and auto-da-fé for which the plurals are 
aides-de-camp, aides-memoire, masters-at-arms and autos-da-fé. 
Looking at the ones which spring to mind straight away, perhaps I
ought to lie down quietly in a darkened room.
> :-)
> 
> Seriously, you can probably provide further examples.

Carol:
How about mothers-in-law and passers-by?

Geoff: 
> This also harks back to sonething Carol wrote on Main a day or so
ago when she asked whether the plural of "deus ex machina" was "Dei ex
machinae" and my answer would be 'no'; it should be "dei ex machina" 
because in the context there should only be one machine.

Carol responds:
Thanks, Geoff. I hadn't thought about there being only one machine,
but that makes perfect sense. I should simply have pluralized the
English translation (gods from the machine) and then translated it
back. Ah. Logic and grammar working together. Wish it were always that
simple.

BTW, logic is the basis of many of the rules of grammar that CJ finds
so objectionable. For example, in math(s), two negatives make a
positive, so, logically, a double negative is a positive: "I don't
want none" means "I want some." Of course, the restriction on double
negatives deprives us of such gems as "Nor this is not my nose,
neither," one of my favorite Shakespearean lines.

Carol, afraid that the topic of this post has bounced around like a
basketball