Can we say "Albert’s birthday is on next Saturday"? and "The concert was on last Saturday"? Does the preposition on in the two sentences have to be left out, or is it optional?
I know we should say "I will send you the proposal next Monday",in which "next Monday" is used as an adverbial modifying the verb send. But in my question, the sentence is "Albert’s birthday is on next Saturday?", in which on next Saturday is a complement after be. Is on next Saturday acceptable here, or still unacceptable just like when it is used as an adverbial?
