Grammar is mainly about structure and usage, and we may be stretching usage a bit here to include diction, or word choice. However, words mistaken for one another bedevil much writing and are more than worthy of discussion here.
It's all spell check's fault. Well, not really, but spell check can be a very deceptive friend. Although it will catch misspellings, it will not catch misuse, and many a "than" for "then" or "their" for "there" or "they're" has flown by the unwary keyboarder.
But what we're talking about here are genuinely confusing words. Do people who make mistakes get their "just desserts" or "just deserts"? Do I "hone in" on this problem or "home in" on it?
Well, one often gets what one deserves, and it's not always ice cream, alas. It's "deserts," and not in the sense of the Sahara desert, but in a rather archaic gerundial form of "deserve" as "desert," akin to "deal" and "dealt."
Let's home in on a real issue: is it "hone in on" or "home in on"? Personally, this misusage bothers me to no end. I never used to hear this, and all of a sudden, it's everywhere! Well, some research turned up an unexpected delight amind the manure of mangled diction in the form of a new term: It turns out "hone in on" is an eggcorn, as the wonderful World Wide Words site points out.
Home is correct; the word refers to the radio beacons pilots used to guide their planes back to home base in World War II. But "hone" has quickly taken over! Especially since one of its earliest citations: George Bush used it in an 1980 speech, and it's spread like wildfire. It's an eggcorn!
Wanna know what an eggcorn is? Home in on this column, next week!