Quote Originally Posted by A.Russell
Quote Originally Posted by MikeNewYork
Quote Originally Posted by A.Russell
Quote Originally Posted by vladz
What verb should I use in the sentence below and why?

None of the letters (is/are) open.

Thank you very much
It is the predicate of a plural subject (the thing that has been opened) that you use "are".

Look at the core of the sentence:

The letter is open.

The letters are open.

Never mind adverbial phrases like "none of"
Actually, you have that backwards. The core of the sentence is "None is open." "Of the letters" is the part that is a modifier and should probably be ignored when choosing a verb.
Depends how you want to break it down. In most cases I would agree that a prepositional phrase would not be core to the sentence structure. In this case, since you can do away with phrases like "some of," "most of," etc, I would suggest that they could be regarded as adverbial.
I have to disagree. There really isn't anyway to turn "some of", "all of", "none of" etc., into adverbials. What verb would they be modifying. Where is the subject of the sentence?

Even you take "none" as the subject of the sentence, I would say "none are" not "none is." (Do you say "some is" or "all is"?) Also, I don't like like the idea of taking "none" as the subject, since what there are none of is implied:

None (of the letters) are open.
You can use the plural verb if you like, but "none" is the subject of the sentence whether you like it or not. If none is not the subject, what is the subject?

The usage of "none", "each" and "either" is different from the usage of "some", and "all".

I do say "some is" and "all is" depending on the meaning. I will bet that you do too.

Some of the cakes are missing.
Some of the cake is missing.

All of the milk is gone.
All of the cakes are missing.
All of the cake is gone.

You are correct about some, all, and any deriving their number from the object of a preposition. That is standard, as the examples above demonstrate. Traditionally, that has not been true of each, either, neither, and none.