Some people say the words "pin" and "pen" differently, but other people say them the same way. When they do, it's called a "pin/pen" merger.
Anne suspects that this merger is a Southern thing, and she’s right! Although dialect features can be associated with race, gender, class, or other demographic traits, some of the best-known features are associated with particular geographic regions. According to the “Atlas of North American English,” by William Labov, Sharon Ash, and Charles Boberg, the “pin/pen” merger is a feature of the English spoken in the southern United States. Furthermore, just as Anne observed, the vowel that these speakers use in words such as “pin” and “pen” really is in between a short I and a short E. The “Atlas of North American English” even has a graph showing the measurable acoustic difference between the ordinary short I and short E vowels and the merged vowel.
Another vowel merger in American English is much more widespread than the “pin/pen” merger. It’s known as the “cot/caught” merger. In dialects with this merger, the word “caught” [kɔt], the past tense of “catch,” has the same vowel as “cot" [kɑt], the kind of uncomfortable bed you might have slept on at summer camp.
Now in my dialect, the vowels in “cot” and “caught” are still distinct. Did they sound different to you when I said them just now? They did to me. In the word “cot,” as in “Squiggly tossed and turned so much that he fell out of his cot,” I used the short O vowel, in phonics terminology. As for “caught,” as in “Aardvark caught Fenster red-handed,” I used a vowel that doesn’t have an easily pronounceable name in the phonics system. It’s sometimes written as an O with a pointed symbol called a circumflex over it. For most speakers with the “cot/caught" merger, both words have a short O sound.
It’s actually somewhat surprising that my dialect doesn’t have the “cot/caught” merger, because I grew up in Seattle, and according to the “Atlas of North American English,” the “cot/caught” merger’s territory covers the western United States. I won’t try to solve that mystery today. The “cot/caught” merger is also prevalent in Canada, New England, and a swath of land stretching from western Pennsylvania south through West Virginia and into Kentucky.
Not only does the “cot/caught” merger cover more geographic area than the “pin/pen” merger; it also covers more phonetic area. Whereas the “pin/pen” merger happens only before nasal consonants, the “cot/caught” merger takes places in a much wider variety of phonetic environments. This opens up many more possibilities for confusion between speakers who do have the merger and those who don’t. For example, it just so happens that Squiggly’s dialect—but not Aardvark’s—has the “cot/caught” merger, and they can tell you a funny story about this one time when Squiggly was talking about a male acquaintance named Don, but Aardvark thought he was talking about a mutual female friend named Dawn. It took about 10 minutes before they got that straightened out. And then there was the time that Aardvark was complaining about a stocker in their local supermarket. Eventually, Squiggly realized that Aardvark was talking about an employee who puts merchandise on the shelves—he stocks the shelves—but only after he’d told Aardvark that he should have called the police about this stalker. Then Aardvark was like, “Why would I do that? I don’t like how he always puts the chocolate-covered ants on the highest shelf, but it’s not a crime!”
You can see how it can cause confusion when words sound alike.
Even with ambiguities like “cot” and “caught,” “Don” and “Dawn,” and “stocker” and “stalker,” there are a few words where even speakers with the “cot/caught” merger distinguish between the two vowels. In particular, the interjection “ah,” which you might utter as you relax into a comfortable bed, still sounds different from “aw,” which you might say when looking at pictures of your friend’s newborn baby.