Substitute or replace?

A few years ago I’d have wondered why this is even a question. At the time (let’s say, ten years ago or thereabouts) I had yet to see them used the way I do now, with what is to me alarming regularity.

I even checked Garner’s Modern American Usage (3^rd Edition) to see if there was an entry with a language-change index rating. There is not.

Then I pulled out my dog-eared Merriam-Webster Dictionary of English Usage (copyright 1989, a full 20 years earlier than Garner’s 3^rd), and lo. An entry. At the time I purchased this book, I had never encountered the usage discussed.

And I should probably tell you what that usage is, shouldn’t I. I get so discombobulated when I see it, I have trouble being clear. It makes me verklempt, I tell you.

I love to cook. I’ve loved to cook for decades now. And I’m well-versed in the usage of the words “substitute” (to put something in place of something else) and “replace” (to take something out and put something else in its place). Or at least I thought I was. Now, I’m no longer sure of myself.  When I read an instruction like “Substitute soy milk for milk to make this vegan-friendly,” I’m pretty sure I’m supposed to leave the milk out and put the soy milk in. Vegans and milk don’t mix well from what I understand. However, sometimes I see this instead: “Substitute milk for soy milk to make it dairy-free.” In the vernacular: WAIT WUT? How in HELL does putting MILK into something render it dairy-free? Milk IS dairy, right? RIGHT?

For a few years I tore my hair out at my day job, which at the time was proofing and copy-editing social media posts and tweets for a national supermarket chain and its subsidiaries. I lost count of the times the confusing usage appeared in recipe blog posts, and every time I clarified it.

Now, I see that in my beat-up copy of MWDEU there’s an entry about this very thing from 20 years ago. It never occurred to me to look at the time, because 20 years ago I’d never seen it “in the wild” as we say. Today, though, I looked. The light dawned a bit late, I guess. Anyway . . .

The key lies in the prepositions. To “substitute X for Y” something means “to use X instead of Y.” To “substitute X with Y” means “to use Y instead of X.”

And the problem is, people in general don’t seem to understand that difference. Prepositions bedevil folks. But come on. Use your head. Which thing do you WANT the cook to use? Is it that difficult to make sure you say what you mean?

Why not just use “replace” if that’s what you mean? “Replace milk with soy milk to make this vegan-friendly.” No one will be confused by that, will they? “Substitute milk for soy milk to make this vegan-friendly” is not the same thing. Not even close. You’re telling people to USE MILK when you say that. “Substitute for” means “Use this thing I’m telling you right here.” I have yet to find an explanation of why people stopped saying “replace” and started using “substitute.” It’s confusing and often incorrectly written with “for.”  We say “replace with,” never “replace for.” If the sense you’re after is “replace,” either use “substitute with” or, better yet, just say “replace with” and be done.

(I should probably thank Grant Barrett of A Way with Words for inspiring this post with a RT earlier today on Twitter, pointing out this very situation of using “substitute for” instead of “substitute with” [or replace, for cryin’ out loud] and thereby creating confusion.)