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I often see "replace with" and "replace by" used interchangeably, but this doesn't sound right to me:

I replaced that component by this one.

I would use "with" in such a sentence. "By" only seems reasonable in passive, although "with" sounds like it would there work too:

That component was replaced by this one.
That component was replaced with this one.

In my native language, the equivalent of "replace by" can only be used in passive, and even then it's a bit weird unless a person is the object replacing something – perhaps this affects my judgment?

Web searches haven't come up with anything conclusive; the results are contradictory and speculative at best.

Are "replace with" and "replace by" interchangeable in active context? What about passive? Are there stylistic reasons to prefer one over the other?

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  • 1
    Related: Substitute X for Y.
    – choster
    Jul 28, 2014 at 15:25
  • Regarding the active voice, I've noticed that mathematics academia uses "replace A by B" almost exclusively, although I'm not sure why. In common conversation, I notice "replace A with B" almost exclusively. Regarding the passive, it seems that almost everyone uses "A was replaced by B."
    – Jeff Grimes
    Apr 27, 2015 at 16:13

3 Answers 3

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OP is right to suspect active/passive has a bearing on preferred usage. From Google Books...

1: Active voice favours with...
The company replaced workers by machines - 9 results
The company replaced workers with machines - at least 180 results1

2: Passive voice favours by...
Workers were replaced by machines - at least 160 results1
Workers were replaced with machines - 8 results

To be honest, I can't say I think there's anything wrong with the "less favoured" versions above, and it would be ridiculous to suggest there's any semantic difference. But note that whereas...

Tom replaced Dick by Harry
Tom replaced Dick with Harry

...are both equivalent (manager Tom took Dick off the team, and put Harry in instead), if we want to put that into the "passive" voice, we can only recast it as...

Dick was replaced by Tom with Harry
...or (more likely, imho)...
Dick was replaced with Harry by Tom

That's to say, if the "passive" form actually specifies the "agent", we have to use by for that agent. So we can only use with for the "replacement" in such (slightly contrived) constructions.

1 Google Books has changed somewhat since I originally did these searches - the smaller values are easy to count so they're accurate, but the "at least" values just reflect how many pages of 10 hits each I could scroll through before GB stopped returning any more (sometimes it just truncates relatively large result sets for no obvious reason). Whatever - that huge reversal of ratios is still unmistakable.

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    With the last sentence in mind. The sentence "Workers were replaced by machines" could be mis-interpreted that the machines are the agent that replaced the workers? In this case I would prefer the "with" version to avoid confusion - (at least in a far future this might happen)
    – Daniel Alder
    Mar 1, 2018 at 14:39
  • @Daniel Alder: I think that would be a somewhat perverse interpretation, so I can't see it would justify hoping that the current preference for by in my example pair #2 should disappear at some far future time. I don't know why the preposition preference should be reversed between active and passive contexts, but it's so strong it seems unlikely to change.
    – FumbleFingers
    Mar 1, 2018 at 16:00
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    I was talking about a future where machines make decisions like "lets replace our workers". That way, the workers really get replaced BY machines (and probably also WITH machines), whereas the BY is the agent and the WITH the object which is used instead of the workers
    – Daniel Alder
    Mar 2, 2018 at 19:53
  • If I say "I replaced something with Harry" it can also mean that I was with Harry when we together replaced something.
    – skan
    Sep 13, 2021 at 18:58
  • @skan: If I say The company replaced workers with machines with machines, that could mean the company used machines to carry out the replacement process. Which raises the possibility of I replaced workers with machines with machines with machines to mean that I was accompanied by machines while using [other?] machines to replace the workers with [yet other?] machines. Not sure if that counts as "syntactic recursion", but it's certainly something to think about. (Any advance on three consecutive with- clauses all with distinct meanings? :)
    – FumbleFingers
    Sep 14, 2021 at 12:35
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In many, (maybe even most?), contexts, replace with and replace by will be interchangeable.

I don't think this has to do with active or passive voice.

Two types of objects can follow replace with and replace by -- the means / method of replacement or the new content. I would say there is a bias for using by to indicate means and with to indicate the substituted content, but I don't think this is an absolute rule:

an example of the former:

Replace numbers by doubling them.

An example of the latter:

Replace all words with codes.

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  • "Replacing by" can also denote that the thing being replaced is also displaced. For example, I can imagine being replaced by a computer, but I'm not sure what it would mean for me to be replaced with a computer.
    – Niel de Beaudrap
    Feb 11, 2014 at 17:33
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    @NieldeBeaudrap replacing me with a computer and me being replaced by a computer both sound find to me. E.g., I am so angry that I was replaced by a computer = I am so angry that I was replaced with a computer. Replaced by is significantly more frequent but replaced with is growing (books.google.com/ngrams/…)
    – virmaior
    Feb 11, 2014 at 17:44
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I have a simple rule. If we are focusing on the replacement function of a subject, we would say: A is replaced by B If we are focusing on the replacement of the subject itself, we would say: A is replaced with B.

Let me know if this works. =)

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  • 2
    What is the derivation of this rule?
    – Chenmunka
    Jan 30, 2015 at 18:37

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