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.
A listener named Anne wrote in with this question:
Have you written anything about the way some people pronounce short E and short I the same? For example, my husband says “pin” [P-I-N] and “pen” [P-E-N] the same way (sort of like a combination of how each is supposed to sound separately), and it fascinates me that he says he can’t hear a difference when I say them differently. I now ask my husband to spell words for me to avoid having any more misunderstandings. He thinks I’m crazy. I grew up in Minnesota and think it’s a Southern thing.
Anne has stumbled into the world of dialects—versions of a single language that have differences in pronunciation of certain sounds, in vocabulary, and even in rules of grammar. The variation that’s tripping up Anne and her husband is an example of something called a vowel merger, which happens when people who speak a dialect stop making a distinction between two vowels. This particular merger is well-known to dialectologists, who call it the “pin/pen” merger. That’s right: They named it after the same pair of words that Anne is asking about, probably because those are the most common words where this merging of two vowels causes confusion.
This merger turns other pairs of words into homophones, too, but usually the meanings are different enough that context clears up any confusion. For example, speakers who have the “pin/pen” merger will also have identical pronunciations for “bin,” as in the container, and “Ben,” the shortened version of the name “Benjamin,” but really, how many situations can there be where you just don’t know if someone is talking about, say, a recycling bin or some guy named Ben? The same goes for “him” the masculine singular pronoun, and “hem,” as in “Aardvark needs to hem his tuxedo because the legs are too long.”
But the “pin/pen” merger doesn’t completely level the distinction between short I and short E. It happens only before a nasal consonant—that is, an /m/ or an /n/. Speakers with the “pin/pen” merger will still hear the difference between words like “pit” and “pet,” “fill” and “fell,” and “miss” and “mess.”