Why "all" is singular here?

The agreement of all depends on what it is all of.
All of the cake is gone.
All of the boys are gone.
The of phrase may be left unstated. Then it's a matter of guessing from context.

All is gone. All are gone.

Thus:
When all (of it / the matter) is said and done ...
All (of it / of t

Wha ta good explanation! I have always chosen are or is according to my senses before.

AbilWhen all is said and done ... All I know is ..

Why "all" is singular here? (We know "all" is also used as plural.)

Hi Abil,
To my ear, the plural has always been extremely low register, and not heard as often now as 50 years ago. "All's I know is, she was drunk as a skunk!" (That's not really a plural, if we're thinking about the same thing

Avangi "All's I know is, she was drunk as a skunk!"  (That's not really a plural, if we're thinking about the same thing.)

Avangi, I don't understand why you have used the apostrophe s with "all".

Thanks CJ, for your brilliant explanation. Like Doll, I too used to apply my common sense while using "is" and "are" with "all".

Avangi is referring to a sort of slang way -- or at least a grammatically incorrect way -- of using all with an s. I've seen both alls and all's as the spelling.
The typical example -- at least in my mind -- is
All's you have to do is ... = All (that) you have to do is ...
I believe the key to the origin of the idiom is in
All (

CJ, thanks a lot. I understand now.