Does All Take Singular or Plural?

According to Merriam-Webster, all can be an adjective, adverb, or pronoun, and it can be used in sentences that involve singular nouns or plural nouns. It can also be a noun itself. When it is, it's considered to be singular. Whether it's used in a sentence with a singular subject or a plural subject is contextual.

Does all take a singular or plural verb?

All is more often used with plural verb forms, though sometimes it is used with singular verbs. This happens when we are referring to all as a totality of items under consideration. Here, all is close in meaning to everything: Is all well with you?

Which is correct all is or all are?

If a writer means “all of it,” she should use “is.” If she means “all of them,” she should go with “are.” So it depends on whether your contributor was thinking of the whole dish or the various things in it: “All [the soup] is returned to a simmer” or “All [the ingredients] are returned to a simmer.”