When using conjunctions in a question to connect two sentences, should I add a comma before the conjunction?

For example,

Why did you leave me to be like this ,and disappear without a single trace?


Why did you leave me to be like this and disappear without a single trace?


(The Writing Center) When a coordinating conjunction joins two independent clauses, a comma is used before the coordinating conjunction (unless the two independent clauses are very short).

This is no hard and fast rule; however, in the case of fairly long clauses a comma seems to be used without fail.

(Examples from CoGEL)

  • He heard an explosion and he therefore phoned the police.
  • Go by air, and save time.
  • Join the navy and see the world.
  • They are living in England, or they are spending a vacation there.
  • She felt ill, and my mother said nothing.
  • I spoke to him before the conference was over, but before he started work.
  • He tried hard, but he failed.
  • John plays the guitar, and his sister plays the piano.
  • Thank you so much for your answer, but I want to know how short the two independent clauses have to be to not have a comma before the their conjuction. – Guest Apr 17 at 8:32
  • @Guest How short can be summed up by a SVO-, SVC-, SVA- structure in which the S, V, C, and A are short (one word, ideally, or two), as in the first and third examples I showed (very short). However, sometimes, in those cases of very short clauses (second example) a comma can still be used. It probably wouldn't be considered a bad mistake to use a comma in the first and second examples. – LPH Apr 17 at 9:03
  • Perhaps the archetypal shortest version is what Julius Caesar uttered aeons back: I came, I saw, I conquered. – user405662 Apr 17 at 9:23
  • 1
    @user405662 This is a sort of coordination but it involves no conjunctions, and in fact if we were to insert conjunctions we would use only one; "I came and I saw and I conquered." is not the usual syntax; "I came, I saw, and I conquered." would be how to write that (ellipsis of the first one). Not using this ellipsis is done as a rhetorical device. However, when more than two conjuncts are used, a comma is placed after the second conjunct according to certain principles that have nothing to do with the length of the clauses. – LPH Apr 17 at 9:33

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