While investigating a recent question on the (mis)usage of substitute, I ran across multiple comments and answers pointing out that replace is traditionally preferred over substitute when swapping X with/by Y, ie., replace french fries with mashed potatoes, not substitute french fries with mashed potatoes.

Here's an example of one such unqualified statement taken from the comments in "replace" vs. "substitute" question.

Replace and substitute do mean the same thing, but in opposite directions. In each case, there is a New and an Old, but the patterns go like this: He replaced Old with New = He substituted New for Old. Having two verbs lets you use either order, to suit your rhetorical purposes. – John Lawler Dec 22 '14 at 4:36

My trouble is I can't interchange replace and substitute this way. I can't think of a single case where this works if you put specific nouns in for Old and New. To me, the verbs replace and substitute take place in mutually exclusive circumstances, and those circumstances govern the choice.

In Substitute X for Y, Cerberus used the example -

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

I can't say that, it's unidiomatic. Mechanics, working on a car, only replace, they never substitute. Replacement is a mechanical act. Substitution is a conceptual act or a matter related to decision-making, done in the planning phase, or on paper. The mechanic ended up replacing the original Bentley wheel with a generic one. He should have noted the substitution on the work order.

When a coach needs to replace a player on the field, he notifies the referee of a substitution. The substitution is presented to the ref. The ref documents it, then the players are exchanged.

In a restaurant, I could request mashed potatoes be substituted for the fries while ordering, but not after I've been presented with a plate full of fries I don't want. At that point, they must be replaced. "Excuse me, but I requested the mashed potatoes as a substitute, can you take that back and replace them please?"

And since I can't choose replace and substitute arbitrarily, I treat the order of the arguments of both verbs as flexible (although replace seems more problematic with the reversed order), and the two arguments as equals when both are present. This evidently represents some kind of change from when there was a proper DO and IDO for each verb.

While the idea that you can just choose the appropriate verb which accords with the argument order is very appealing, does anyone really do this anymore? If so who? When do substitute/replace not have distinct usage outside of argument order?

  • Now that you mention it, there seems to be just a touch more like-for-like in replace than in substitute: a replacement is supposed to carry on the same function, whereas a substitute might bring something new.
    – Lawrence
    Commented Dec 10, 2017 at 23:56
  • I for one, was lost in the sophistry of that, Phil. What's left unsaid in The mechanic had to substitute a generic steering wheel for the Bentley's, please?. Are you suggesting that should mean the same as The mechanic had to replace the Bentley's with a generic steering wheel, or what, please? Commented Dec 12, 2017 at 22:16
  • @RobbieGoodwin We may be talking past each other here a bit. But the contention that those two sentences ought to be identical isn't mine, but rather how I interpret John Lawler's statement. To me, they aren't the same, and the first isn't really possible without changing some of the other words. I can not use substitute to mean 'remove the Bentley steering wheel and install a substitute steering wheel". I can use replace for that.
    – Phil Sweet
    Commented Dec 13, 2017 at 1:35
  • thanks Phil and don't you think the only point is whether those sentences are identical or interchangeable or even equivalent? What else matters, please? Commented Dec 13, 2017 at 23:37


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