Add chopped potatoes, mushrooms, and herbs, and cook for 20 minutes.

Is a comma necessary before the second "and"? And if it is necessary, why? Please help find a grammar rule for this case.

  • 1
    Commas are not determined by grammar, but by intonation. Say it out loud; do you hear an intonation curve there? If so, put a comma to mark it; if not, no comma. Sep 13 at 21:18
  • Since you've got a compound sentence (albeit imperative, so you don't "see" the subject), this may be helpful: Comma before "and" in compound sentences?
    – livresque
    Sep 13 at 21:36

A comma is necessary before the second "and". This is because it is being used as a conjunction to join two independent clauses ("Add chopped potatoes, mushrooms, and herbs", and "Cook for 20 minutes") into a single compound sentence. When "and" is used in this way, we must mark the separation between clauses with a comma.

To help illuminate the discussion, some further relevant context is that a comma is not necessary before the first "and," because this is the optional comma placement known as the "Oxford comma" -- it is highly controversial in terms of taste (i.e. you'll very rarely find one other who both chooses to use the Oxford comma in some cases, yet omits it in others) but in terms of correctness, both ways are traditionally accepted in most contexts and according to most official styles.

  • 2
    I wouldn't go along with you. Consider this attested example "It was a perfect day and everyone was in good spirits". Here, we have a coordination of two main clauses, but no comma.
    – BillJ
    Sep 14 at 8:51
  • Oxford commas have already been discussed in great depth on ELU, Dan. // So has the acceptability of dropping the traditional comma before a coordinator (and BillJ gives an obviously acceptable commaless example above). Another: 'Go home and get some sleep'. The comma is totally optional; the author can indicate how they want the sentence to be read, with or without a pause. // Here, though, the fact that there is an 'and' between the last two list elements means that omitting the pre–clause-coordinator comma invites confusion; it is needed. Oct 14 at 11:54

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