All you can see is

Anonymous"All you can see through the window of an aeroplane is clouds". Why do we use the plural form "clouds" after singular verb "is" in this sentence? Is this sentence grammatically correct ?

It's correct. Agreement is with the subject (all), not with the complement. (This is the so-called "pseudo-cleft" structure, by the way.)

I think there may be BrE/AmE differences here (similar to the "is"/"are" differences observed with collective nouns?) as the following are all OK to me, and in many cases preferable:

All you can see through the window of an aeroplane are clouds.

All I have are these documents.

All I know are a few facts about it.

Wha

Whoops! I edited to change one of those sentences before I knew someone had commented on them!

In any case, if I say them a few times, I can easily get used to the "are clouds", "are these documents" (etc.) versions, but approaching them cold, they still sound wrong to me.

This issue has already been discussed a couple of times, if I'm not mistaken. What I remember is that both a singular and a plural verb are possible in such structures, depending on personal preference, style, emphasis, etc. I don't think this is a grammatical feature that is expected to be fixed for most speakers. I bet it varies a lot from dialect to dialect, most native speakers might not even

KooyeenI don't think it's worth worrying too much about it.

Amen.

CJ