I'm describing how you write something down (specifically, an array initializer in JavaScript, but that's not important), and find myself intrigued by the choice of using "separated by" vs. "separated with." I wonder if there are rules, or whether it doesn't really matter which you use.

As a native English speaker (mostly of American English but influenced by British English), my largely unschooled instinct is that "separated by" is more of an observation of fact ("As we can see in the diagram, the entries are separated by commas"), and that "separated with" is more related to an instruction ("When writing...put the entries between the square brackets, separated with commas")... I think part of the reason I feel that tug toward "with" is that I'd definitely use "with" in the imperative sentence "Separate the entries with commas."

Is there language logic to back that up? And/or is my unschooled instinct simply wrong? :-)

In this case, I'm primarily interested in informal but professional American English usage.


4 Answers 4


In a passive construction with a participle like separated, by and with have different functions.

  • by marks an agent phrase: The fighters were finally separated by the referee.
  • with marks an instrumental phrase: The fighters were finally separated with a crowbar.

When you're talking about metaphoric separation -- item boundaries in a left-to-right line -- you have the option of treating the "separator" either as an agent itself, or as a tool (of another agent).

Interestingly, this is the same range of meanings as the agentive -er suffix:
a typewriter is an instrument, but a ghostwriter is a human, and therefore an agent.

  • The entries are separated by commas is the agent interpretation,
    a passive version of Commas separate the entries.

  • The entries were separated with commas is the instrument interpretation,
    a passive version of Indef separated the entries with commas.

Note the different tenses required above; being separated is either an event or a state. Permanent states normally take present tense (My car is red even though it's been red for 5 years). Events can be located on the time continuum, usually in the past tense. So past tense is likely to signal reference to an event, and present tense to a state.

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    This is a 50-y-old single malt answer. Sorry, Bourbon. Commented Oct 4, 2014 at 20:12
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    I've never liked Scotch, but had a 'Black Bush' when trying to avoid pneumonia on the Dingle Peninsula earlier this year. I was so impressed that I've got a couple of bottles in for Christmas. Some day, Catherine and I will go back to see the Dingle Peninsula (most of the rest of the tour was delightful). Commented Sep 7, 2015 at 15:05
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    I loved Dingle, but there were a lot of soft days. Want to get back to Ireland sometime; I've only been to the other side once and now I'm a continent and an ocean away. And don't drink much any more, alas. Commented Sep 7, 2015 at 15:10
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    (Not sure how I managed not to come back to this for so long.) The commas in the target sentence are instruments, of course, so that probably explains my "with" instinct. Thank you. Commented Feb 29, 2016 at 7:34
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    Charles Fillmore pointed out the difference between "The house was destroyed by fire" and "The house was destroyed with fire", the last implying the participation of some agent (the arsonist).
    – Greg Lee
    Commented Jun 21, 2019 at 23:01

Your use of with in this context is entirely appropriate.


  1. a. By the means or agency of. b. By the presence or use of. (AHDEL)

Some examples of such usage:

  • Items in lists are usually separated with commas... (Grammar Monster)
  • How to: Display an Item List Separated with Commas - MSDN
  • The nonessential adjective clause (like other nonessential elements) SHOULD be separated with commas. (Towson.edu)
  • Nonessential appositives are set off from the rest of the sentence with commas. (The Editor's Blog)
  • ...as many different addresses as you want as long as the addresses are separated with commas. (cmu.edu)

I think you can feel safe in doing so.


There is a similar question here.

The short answer is: prefer by over with. It is not that with is wrong, but it is commonly used in cases like:

This was done with the help of that.

In most cases by and with are interchangeable, yet it could vary in cases like:

I smell with (not by) my nose.

One of the interchangeable cases is:

This is indicated by/with a green light.

If you are writing documentation for your application, use the correct word for readability. For instance,

This should be instantiated by passing the arguments A, B and C. They should be separated by a comma. This should be called with D and E.

  • It seems to me the linked question is using quite a different sense of "by," it would never occur to me to use "with" in that situation. (I'd even go so far as to say it was wrong.") Whereas the case in my question is much more ambiguous (or so it seems to me). It would be a definite "with" if the sentence were "Separate the entries with commas," for instance. Commented Oct 4, 2014 at 18:04
  • Please support your answer with links. That makes your answer stronger, and more likely to be viewed as correct (as you will at least have researched it enough to support it). Otherwise it's only opinion. Commented Oct 4, 2014 at 18:32

My knowledge tells me that "by" is mostly used by Americans, and "with" is mostly used by the British. Otherwise, either word can work.

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    What is your knowledge? Please support your answer with links. That makes your answer stronger, and more likely to be viewed as correct (as you will at least have researched it enough to support it). Otherwise it's only opinion. Commented Oct 4, 2014 at 18:32

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