My question is that in the sentence:

The thief opened the door with the duplicate key.

Why can't I use by in place of with?

  • 2
    You just can't. You could say "The thief opened the door by means of a duplicate key," but that's about it.
    – Robusto
    Mar 12, 2015 at 9:57
  • 1
    The second leaves the reader wondering why the duplicate key was placed right next to the door.
    – Hot Licks
    Mar 12, 2015 at 12:33

3 Answers 3


Doubtless as a result of historical changes in meaning and ellipsis, the meanings of prepositions in specific modern-day expressions are legion, often etically unpredictable, and not infrequently apparently illogical. There are broad rules, but they are very broad, and exceptions are many. Avoidance of ambiguity is desirable, but not always achieved: even 'The thief opened the door with the duplicate key.' is ambiguous (instrument (= using), or identification (= which had) of the door?)

David Thatcher, in Saving our Prepositions, writes [re-formatted]:

Greenbaum (103) cites “an empty aspirin bottle was found by the deceased.” This, he says, “sounds as though the dead person found the bottle rather than, as was presumably meant, that the bottle was found beside him.”

The art section of my local newspaper ran the headline, “the world of ballet has been blessed by many fine composers,” suggesting that composers, en masse, have been usurping a priestly prerogative. By, of course, should have been with. The broad distinction is that by denotes the agent, or essential agent, of an action, and with the instrument of an action. Compare “he was struck by the sun” with “the sun struck with its rays, “the tree was shaken by the wind” with “the wind shook the tree with its strong hands, “”the city was destroyed by fire” with “he destroyed the city with fire” (examples cited by Fernald 189).

In practice, by and with are used less strictly, but “where with or at can reasonably be used instead of by, they should be” (Greenbaum 103).

That the distinction is not universally made is shown by examples such as

We must do it by long division. [internet]


The secret doesn't lie on whether you made it by machine or by hand but on the embroidery supplies you use to craft it. [internet]

both showing instrumentality.

But in OP's example, 'with' is the accepted choice. This is probably strongly connected with the fact that 'key' is concrete whereas 'by hand', 'by long division' ... show methods (long division being abstract, and hand in this expression intermediate).

  • In the two examples you have provided, it is because the implied using is missing. "We must do it by using long division." "The secret .. made it by using [a] machine or by using [your] hand .." Mar 12, 2015 at 13:21
  • What is 'because the implied using is missing'? If omitting a using is always acceptable, what happens between 'The thief opened the door by using the duplicate key' and *'The thief opened the door by the duplicate key'? I'll not accept reasoning like 'it is because the implied using is missing [that the shorter expression is acceptable] without evidence. Is this just guesswork? Mar 12, 2015 at 14:50
  • Charles Fillmore observed that "The house was destroyed with fire" implies the action of an unnamed agent, but "The house was destroyed by fire" does not.
    – Greg Lee
    Mar 12, 2015 at 16:32

As a general rule of thumb that I use with my students, we use with to show the instrument itself. It must be being used as an instrument operated by an actor in the sentence. It is nearly always a noun:

  • They cleaned the windows with a shammy
  • They beat him with their fists
  • I opened the door with my key
  • I write with my pen
  • I built this house with my own hands

We use by to show a method by which something was achieved. We can use a gerund participle clause or a noun:

  • I evaded the police by hiding in the shrubbery
  • He did it by means of a quick lap of the grounds
  • I go to school by bus

And of course we use also by to indicate the agent of an action. Tha action may be implied:

  • I was bitten by flies
  • The massacre of the Daleks by the Vogons
  • A play by Shakespeare

Of course, this is just a rule of thumb. There are many exceptions as well as grey areas. For example, sometimes we may use a noun to indicate either a general method or an instrument:

  • We paid by card.
  • We paid with a card.
  • "By" can also express cause. "He annoyed her by picking his nose" = "His picking his nose annoyed her".
    – Greg Lee
    Mar 12, 2015 at 16:26
  • @GregLee Yes, although it could be considered a method too in that example! Mar 12, 2015 at 16:28
  • 1
    That's true; it's ambiguous. It's hard to find unambiguous "cause" examples that everyone accepts. "The thunderstorm annoyed her by delaying the picnic."
    – Greg Lee
    Mar 12, 2015 at 16:40

Who said that you should use the preposition by?

According to Cambridge Dictionary Online, the meanings of the prepositions are the following:

with - "using something (method, instrument)", e. g. Fix the two pieces together with glue.

There is no any meaning of the preposition by to be possible in your case. The possible choice could be:

by - "used to show the person or thing that does something (agent)", e. g. The book was translated by a well-known author.

If by is used, there is the meaning that "duplicate key" is a person which opened the door but actually the thief opened it.

  • Who said that CDO was comprehensive? AHDEL has by - 2. With the use or help of ... [did it by long division / a different method / machine]. Unfortunately, this seems to licence 'The thief opened the door by the duplicate key.' But this is unacceptable. The distribution of prepositions is very idiosyncratic, and there are so many exceptions to rules-of-thumb that one wonders about their value. Indeed, many dictionaries avoided lengthy lists of definitions for prepositions for many years. I wonder how many senses OED lists for 'by'? Mar 12, 2015 at 11:14
  • @EdwinAshworth a good point, yes, there are many exceptions, but the question is not about the exceptions. I only wonder if these exception can be verified by the historical grammar approach. Mar 12, 2015 at 11:16
  • 1
    The question is not about exceptions, but your answer fails to even mention exceptions, merely showing that the usage OP asks about isn't mentioned in a mid-level dictionary. Robusto's 'answer' is a better reflection of the actual situation here, though it is necessarily frustratingly undetailed. // There have been many studies of the quirks of modern-day usages of prepositions, including how they may have arisen. Some are mentioned elsewhere on ELU; all are complex, and probably too lengthy for this website. Mar 12, 2015 at 11:25
  • 1
    "By" doesn't show an agent -- it marks the original subject of a passive. This example shows that: "Ohio is bordered on the north by Lake Erie."
    – Greg Lee
    Mar 12, 2015 at 16:37
  • @GregLee Not sure about that last comment there. How about "the slaughter of the peasants by the junta"? It might be the case that the "original subject" of a passive is indicated by by, but that doesn't mean that by doesn't indicate agency ... Mar 13, 2015 at 1:20

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