Should I use plural or singular form in the following sentence?

The sincerity of pronouncements by multinationals is/are anybody's guess.

My understanding is "sincerity" is an uncountable noun, and should be followed by "is", but it does feel a little weird to use the singular form when it is modified by "multinationals" which is clearly plural.

I feel like this is a very basic grammar question and I am sure I have studied about it in my high school English class. But I don't know how to search for it since I don't know what specific grammar rules I am looking for. Thanks for the help in advance.

Solution 1:

The verb should be "is."

Compare:

Multinationals are ...

Pronouncements by multinationals are...

The sincerity of pronouncements by multinationals is ...

If multinationals or pronouncements were the subject, the verb would be in plural form. However, when sincerity is the subject, and the other two words are within prepositional phrases, it is only the number of "sincerity" that affects the number (singular or plural) of the verb.

If you have a different sense, it is likely because of the proximity of other nouns to the verb. However, relying on proximity without attending to whether they're part of a prepositional phrase would be an error.