Is it “all the” or “all of the” in English? - Jakub Marian
“All” can be used as a predeterminer to further specify a noun. You can say, “All my friends are eating pizza.” However, as we have already seen, “all” can also be a pronoun, and just like we can say “all of them”, we can also say “all of my friends”. Both variants are grammatically correct:
When Do We Use "All of the," "All the," or "All"? – Ellii Blog
ellii.com › blog › answering-students-grammarSep 11, 2012 · All of the students in my class studied hard for the test. (plural count noun) I used all of the paper in my notebook to write my essay. (non‑count noun) all the + Ns. Explain to students that this pattern is the casual form of the “all of the + Ns” pattern, where “of” is simply dropped to shorten the phrase. Most textbooks don’t mention it, but shortening phrases is very common in English, especially spoken English, and should be taught to your students.