Q: A contributor to a publication I edit has complained that I wrongly changed the sentence “All is returned to a simmer” to “All are returned to a simmer.” Is she right? If so, oops!
A: “All” is a two-faced word. It can be either singular (“is”) or plural (“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.”