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An awful lot of people seem to use the phrase "substitute X for Y" to mean "replace X with Y", while I've always used and understood it as "replace Y with X". This makes sense to me, given that a substitute is the replacement, not the thing which has been replaced.

I thought I might be able to figure things out from a dictionary, but now after seeing two sorts of definitions, I'm even more confused:

  1. to put or use in the place of another
  2. to take the place of; replace

The first one suggests that the object will be the substitute (replacement), the thing put into place, while the second suggests that the object will be the thing which has been replaced.

Is one of these usages more correct in any sense? (I know this is probably a pointless question, since people will continue to speak the way they speak.) Is there perhaps a difference between American and British English?

And most importantly, is there any reliable way to tell what someone means when they ask how to substitute honey for sugar, or is the verb simply guaranteed to cause confusion?

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5 Answers 5

up vote 21 down vote accepted

This is probably the source of the confusion you noticed:

  • “Substitute…for…”first replaces second.
  • “Substitute…with…”—second replaces first.
  • “Replace…with…”—second replaces first.
  • “Replace…by…”—second replaces first.
  • etc.

“Substitute…for…” is an unusual case when it comes to the order of this sort of phrase, but actually the preposition is all-important. Just think of for as meaning in favour of or in place of.

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I do understand all of these exactly as you say; it was only the second definition which seemed odd, but you've certainly clarified where that one is used. As for the incorrect usage, I guess it's just that - something I have to try to notice and take into account. I'd been half-hoping I was being overzealous and there weren't quite so many people saying the opposite of what they meant. (This is really annoying over on cooking.stackexchange.) –  Jefromi May 1 '11 at 1:47
    
I think there's a good reason why people don't take much notice of the particular operator specified (for or with). As soon as you hear the word substitute you pretty much know one of the two important words following will already be 'on the table', so to speak (it's in the sentence being considered for revision, for example). Once you identify that 'existing' word, you know the other is a proposed replacement. The third word is effectively just 'noise' in this context, so neither the speaker nor the hearer really care about it. –  FumbleFingers May 2 '11 at 0:30
    
@FumbleFingers: cooking.stackexchange.com/questions/14440/… –  Jefromi May 2 '11 at 3:13
    
@Jefromi: That link isn't about for/with - it's about the problems caused when X and Y in OP's example aren't directly replaceable entities because of uncertainty about actual quantities. We can all talk about replacing sugar with sacharine, but if you didn't make appropriate quantity adjustments you'd end up with something an awful lot worse than just an aftertaste. –  FumbleFingers May 2 '11 at 3:31
    
@Fumble: But the problem is that the OP there is using "for" with the entities swapped, i.e. as if it were "with". And my point was to provide a counterexample to your statement that you generally know which item is the replacement - you don't always! –  Jefromi May 2 '11 at 14:16

The preposition controls the meaning. "Substitute X for Y" means what you think it does: the X will replace Y.

"Substitute X with Y", however, reverses the meaning: Y will replace X.

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I agree with Jon and Henry. However, it should be noted that the use of to substitute X with Y is usually not recommended by style books: it is a blend of the old expressions to substitute X for Y and to replace X with Y. It may have emerged out of confusion between the two. You substitute the new thing for the old thing, and you replace the old thing with or by the new thing. There is also simply to substitute X, without a Y:

Petrochemical oil is a very useful type of fuel with a high energy yield; if we substitute vegetable oil, we may have less pollution, but we'll need larger fuel tanks.

This use of the verb to substitute X as above is quite common; you always substitute a new thing, vegetable oil. What you substitute it for is then implicit; in this case, it would be the petrochemical oil from the first clause. It fits with to substitute X for Y (you substitute the new thing), but it clashes with to substitute X with Y; that is another reason not to use the latter.

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The traditional construction is like this:

The mechanic had to substitute a generic steering wheel for the original Bentley wheel.

The substitute is the thing you substitute; the original is what you substitute it for. It is perhaps easier to remember if you know the origin of the construction. The word substituo means "to place under, to substitute" in classical Latin. From statuo, "to place, to cause to stand", and sub-, "under". The prefix sub- is used in a way similar to supplant, suppose, the latter meaning "to take a theory in place of a fact" (we suppose something because we don't have the facts).

It is also possible to mention only the substitute:

The recipe said she needed "bacon". She hated bacon. She decided to substitute parma ham.

Because some people have forgotten how to use the construction, probably caused in part by contamination with replace, you will sometimes see it used in various other ways; however, because confusion is quick to ensue, style guides recommend that you use it like this.

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That does not ring true in my easy - I strongly miss it for or it with parma ham in the second part... Am I correct or just non-native ;) –  mplungjan Jul 15 '12 at 8:48
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@mplungjan: With is strictly speaking also a contamination with replace. As to substitute without for, you can see a few examples from books here: google.com/… –  Cerberus Jul 15 '12 at 9:06
    
Yes. The two verbs have complementary syntax. One replaces Old with New, but substitutes New for Old. Rather like one buys Commodity for $$ vs pays $$ for Commodity. The prepositions vary all over the lot, of course; but then they always do. –  John Lawler Jul 15 '12 at 16:45

That’s fine if you put it in two sentences like that, it becomes clarified by context. But too many people describing recipes will get it wrong where the context really does matter. For example:

I used my grandmother’s recipe, but I substituted apples for pears.

That sentence above is totally unclear, particularly if you don’t have access to Grandmother’s recipe. This should correctly mean that Grandma specified pears, but I used apples instead. But 80% of people would interpret this the opposite way. The result is confusion.

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