Some pairs of words are like Ashley and Mary-Kate Olsen.
Let me explain.
The Olsens were the youngest cast members of Full House, a popular TV series that had its original run from 1987 to 1995. They played just one character, the daughter of a widowed sportscaster.
The girls were cast jointly for the same role because at age nine months they looked very much the same.
They’re not identical (monozygotic) twins, but it was difficult to tell these non-identical (dizygotic) twins apart.
English has many pairs of words that are like the Olsen twins: not identical, but oh-so-close in appearance. So close that writers and editors must be careful not to let the wrong one slip into publication.
For example: then and than. Use the latter for comparisons (“Susan is taller than Doug”).
Or how about home and hone? Properly speaking, one “homes in on” a target. One does not, as I saw recently in a headline, “hone in on” it.
Similarly, reign is often confused with rein. To limit or control something is to “rein it in,” as if that thing is a horse responding to tugs on a rein. If I had a nickel for every time I saw a mistaken “reign in” … well, I’d have a lot of nickels.
Then there’s the confusion between complement (to complete or go well with another thing) and compliment (to express praise or admiration). And discreet (showing discernment; careful) and discrete (distinct or separate).
I’ll give you one last pair: peak (a mountain’s summit) and peek (a quick glance). I’ve confused the two once or twice.
All these pairs have nearly identical shapes on the page or screen, so you may not notice on a quick glance that you’ve typed the wrong word. Using the wrong word can hurt the clarity of your message.
It’s important to remember that spell-check won’t necessarily catch mix-ups of these and other non-identical twins. A good editor will, though.
Well, almost always. Pobody’s nerfect.