Read this sentence from a news story about whether vegetable oils can really lower your cholesterol as much as people say they can:
We’re often told to substitute saturated animal fats for healthier vegetable oils…. (link: http://www.care2.com/causes/are-those-healthy-heart-vegetable-oils-really-good-for-you.html#ixzz2l1nTJIft. This sentence was brought to my attention in a posting to the American Dialect Society email list made by Larry Horn.)
You might be thinking I’m going to comment on the use of healthier instead of more healthful, but I’m not! Healthier is just fine, and you can find out more about that usage question here or in my book 101 Troublesome Words You’ll Master in No Time. [Amazon, Barnes & Noble, Indiebound] Oops; I guess I did comment on healthier after all, but what I actually want to talk about is the verb substitute.
Back to the sentence with substitute:
We’re often told to substitute saturated animal fats for healthier vegetable oils
Now here’s another sentence with substitute, which I got from the Corpus of Contemporary American English:
If every American substituted something meatless for one chicken dish every week, it would save as much carbon dioxide as taking 500,000 cars off the road.
Did you hear the difference? In substitute saturated animal fats for healthier vegetable oils, the verb substitute has the pattern “substitute OLD for NEW”: saturated animal fats for healthier vegetable oils. In substitute something meatless for one chicken dish, the verb substitute has the pattern “substitute NEW for OLD”: something meatless for one chicken dish. What’s going on here? Which one is right?