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I've always been under the impression that, in standard English, "replace" is only paired with "by" in the passive voice, and that "replace with" is the correct active counterpart of "be replaced by":

It can be replaced by a new one. (Right)

We can replace it with a new one. (Right)

We can replace it by a new one. (Nonstandard)

All the related discourse I can find seems to agree that the active "replace by" is unidiomatic.

However, I've noticed way too many counterexamples over the years to ignore. I'm talking about technical papers, textbooks, and the like—definitely not limited to uneducated or unscrupulous writers. The following slide from a lecture is just one typical example.

Image text: "We assume here that the weight of the member is small compared with the force it supports. If it is not, we can replace the weight W of the member by two forces, each W/2 with one force acting at each end of the member."

Why is this? Is there any documented rule that says this is acceptable in some category of technical vernacular? Why is it so common, yet so rarely talked about?

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    I never learned the use of "replace" with the examples you mention but that is its use. Though perhaps unidiomatic it does not sound at all out of place as far as my American ear. I often hear people starting a sentence with one thing in mind only to finish with another. The use here is the second example turning into the first. Perhaps not fine writing but not bad English.
    – Elliot
    Apr 13, 2020 at 4:24
  • That is my question though, I'm asking whether it's prescriptively correct in formal writing or not. Apr 13, 2020 at 5:03
  • The active voice in English is a bit of a dog's breakfast. The rule seems to work quite well for the classic examples of active voice, but the truss example is not one of those. It serves more to licence an action than to enact it. And the replace here is actually a different sense of the word, since the weight is still understood to be there. We can treat the weight W of the member as two forces, each w/2, acting at the pinned ends of the member. Like Elliot, the truss example sounds fine to me, but most active voice uses do not.
    – Phil Sweet
    Apr 13, 2020 at 10:16
  • @PhilSweet That's an interesting take on it. Apr 14, 2020 at 2:38
  • The dirty oil filter was replaced by the mechanic. Jun 14 at 18:28

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This is valid, though according to Ngram it used to be more common (relative to the version with "with") than it is now.

TfD gives this definition, excerpting the part dealing with the version with "by":

replace someone or something by someone or something

to remove someone or something and add someone or something in place of the first. The manager replaced two workers by a machine.

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