I am German, and we have a completely different comma system. Due to various reference on this great site here, I bought The Penguin Guide to Punctuation and worked through the comma section. What can I say, I'm shocked about my lack of knowledge, although the comma rules in English are far more easier than in German. I instantly took one of my books and verified correct commas there.

There was one sentence, which I believe was incorrectly punctuated:

Memory can be implemented by delays, and wiring by various walls to guide the one extra bit per site needed to represent the walls.

In my opinion a gapping comma is missing, because the phrase can be implemented was left out in the second part. Therefore, I would add a comma

Memory can be implemented by delays, and wiring, by various walls to guide the one extra bit per site needed to represent the walls.

Now we have to commas. The first one joins the two complete sentences, and the second one marks that between wiring and by various a phrase is missing.

Can someone tell me whether I'm wrong here?

  • 3
    People writing in English don't always use the comma rules properly, as these aren't a piece of grammar you absorb when you learn to speak, and they also aren't taught intensively in schools. I'd say that gapping commas are optional in some cases, but that you can't go wrong if you use them, and that this sentence is much clearer if you use one. Sep 11, 2013 at 12:35
  • I've read that sentence several times, and I've come to the conclusion that it needs to be rewritten: it's too long and it's too convoluted. If people are trying to deduce what the meaning of a given sentence was supposed to be then, as a writer, you've failed to communicate what it was that you thought that you had to say. Complex thoughts need to be broken down into simple statements. The last thing that you want to do is to make a complex idea unintelligible.
    – user233229
    Apr 26, 2017 at 2:20
  • As with prototypical parentheticals, the offsetting commas round the 'and X ØØØ by Y' gapped structure (ØØØ is here the deleted 'can be replaced') can be deleted if they don't really improve clarity. Though here, as 233 says, a rewrite clarifies more satisfactorily. Dec 1 at 11:11

2 Answers 2


I don't believe you can insert a gapping comma there for two reasons.

  1. Because it puts and wiring into parenthesis.

    That is, your second example can be read as

    Memory can be implemented by delays by various walls to guide the one extra bit per site needed to represent the walls.

    I don't think that's right.

  2. Because the first comma could be read as a sort of Oxford comma:

    Memory can be implemented by delays and wiring, by various walls to guide the one extra bit per site needed to represent the walls.

    That doesn't look right either.

Not every omission needs a gapping comma, and there are some instances as here where adding one is a hindrance to understanding.

  • 1
    The author of the book gave a very similar example. He claims that the following is correct: "Italy is famous for her composers and musicians, France, for her chefs and philosophers, and Poland, for her mathematicians and logicians." Wouldn't this invalidate your argument? and Poland has two commas: one Oxford listing comma and one gapping comma.
    – halirutan
    Sep 11, 2013 at 12:50
  • 3
    No. I'd lose the commas after France and Poland, for the reasons I gave. Or use semicolons between the list items.
    – Andrew Leach
    Sep 11, 2013 at 12:52
  • But if you leave the gapping comma out, it can be read as: Memory can be implemented by delays, and (can also be implemented by) wiring by various walls to guide the one extra bit per site needed to represent the walls. I think it's best to rewrite the sentence, but if you have to decide between putting in and leaving out the gapping comma, my opinion is that it's clearer with it in. I would recommend changing the comma after "delays" to a semi-colon to clarify (even if the punctuation police would claim that's incorrect). Sep 11, 2013 at 14:20
  • @PeterShor Only if you interpret the existing single comma as an Oxford comma. I don't. Actually I don't believe the sentence is unclear at all. And now that I see that the Penguin Guide is written by Trask, I feel entirely vindicated!
    – Andrew Leach
    Sep 11, 2013 at 14:27
  • @Andrew: that's the way I interpreted it when I first read it, until I got to the last part of the sentence and realized it didn't make any sense with that interpretation. Sep 11, 2013 at 14:28

Stick with the second one as the Oxford comma clearly adds the pauses in the right place. The reader naturally does the rest so the parentheses issue is not a problem.

Commas are there to add pauses and make lives easier. Use them as much as needed and your writing should sound like it would be spoken.

  • Oxford commas only occur in lists of three or more items (if they're used at all). Dec 1 at 11:04

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