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replaced by or replaced with

A colleague just asked me which of the statements below was correct:

“System A will be replaced by System B” or

“System A will be replaced with System B” 

Note that in this context System A and System B are competing software packages that are removed / installed by third parties. System B does not install or remove System A. 

I thought that either was correct - is this right? I could not tell her which was better or why or in what contexts I would choose ‘by’ over ‘with’ or vice versa. Can anyone propose guidelines for usage?

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Strangely, dictionaries don't seem to be a lot of help here. According to Oxford Advanced Learner's Dictionary it looks as though they're interchangeable -
'replace somebody/something with/by somebody/something -
"It is not a good idea to miss meals and replace them with snacks." '

But Longman's has this example - "They replaced the permanent staff with part-timers".- where I don't think "by" would work.

And in this example from the Free Dictionary - "the manual worker is being replaced by the machine" - I'm not sure "with" would really work.

And here are two from Merriam-Webster's:
"I replaced the old rug with a new one."
"Paper bags have been largely replaced by plastic bags."

In fact all the active examples with a preposition I can find in dictionaries have "with", and all the passive ones have "by". So It looks to me as if "with" goes better with active clauses and "by" with passive clauses.

Ngram certainly suggests that in the passive "replaced by" is much more common than "replaced with" -

And it seems to me to do the opposite in the active, but I'm not 100% sure about how to do a wild card here. -

There is a suggestion on another forum that in the passive version, if the thing doing the replacing is the agent, it should be "by", but in the plastic bags example, the bags are hardly the agent, so I don't really go along with that.

And the commenter then gives this example - "Employees were replaced with robots" - which seems to work, but compare it with the Free Dictionary's very similar - "the manual worker is being replaced by the machine"

The Free Dictionary example and the second M-W examples are about general situations, and the "employees" example is about a specific occasion, so perhaps that might also have something to do with it.

Warsaw Will November 16, 2012, 11:39am

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The leaking pipes were replaced by the plumber.
The leaking pipes were replaced with new ones.
The night staff was relieved by the day staff.
The night staff was replaced with robots.
The plumber replaced the leaking pipes with new ones.
The hospital management committee decided to replace the night staff with robots.

When the voice is passive and an agent (human or not) is active in the scenario then 'by' is the word required. If the voice is active then the agent is the subject. In general one is advised to avoid passive if possible. That way there is always a clear guilty party. Using the passive keeps the identity of the agent hidden. Very useful in the case of litigation ;-)):

The day staff replaced the night staff. (with themselves)
The plumber replaced the leaking pipes. (with new ones)

Thomas Smith November 20, 2012, 9:59pm

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@Thomas Smith - I have some sympathy for your argument, and I've seen it elsewhere, but in these dictionary examples can we really call the machine or the plastic bags agents? They are hardly the ones doing the replacing. Aren't they just like your robots?

"the manual worker is being replaced by the machine" - the Free Dictionary
"Paper bags have been largely replaced by plastic bags." - Merriam-Webster

Or have these dictionaries simply got it wrong?

Warsaw Will November 21, 2012, 4:36am

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Re: " It looks to me as if "with" goes better with active clauses and "by" with passive clauses...", I'm not sure that really tells the whole story, but it certainly seems on the right track. I'd like to propose the following (completely without justification):

"Paper bags have been largely replaced by plastic bags."

means that paper bags are no longer used. Plastic bags are now in common use, serving the same purpose, making paper bags obsolete.

"Paper bags have been largely replaced with plastic bags."

means that paper bags were, say, physically on the shelves in some actual storeroom, and someone removed most of them, putting plastic ones in their place.

Just a thought.

porsche November 22, 2012, 10:42am

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@porsche - and rather a good thought, I think. And there might be a good reason. In your second example, we know that somebody (or some people) 'actively' replaced them, so it would be strange to think of the bags as agents. In the first example, however, it's more a process, where perhaps the agent is not so clear. Just another thought.

Warsaw Will November 23, 2012, 4:53am

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