Here is a mystery. I received a message from Stefani O’daniel today that contained this complaint:
“Please tell me if I am right or wrong. I hate didn’t pronounced [diddent], not [didnt], wouldn’t pronounced [wooddent] not [woodnt], and couldn’t pronounced [kooddent] not [koodnt]. Which is right?”
“I’ve heard these words pronounced this way for the past 30 years now and iits irritating. I was told the words are pronounced this way because that is the correct pronunciation.”
I became aware of my students using these pronunciations in the 80s. Where it came from, I cannot say but I’m very suspicious of California, Valley Speak, so to speak.
N in the English language now can be pronounced as a vowel when occurring between consonants. The schwa (UH or on this website [ê]) has disappeared from the language before N between consonants. The tongue does not move between the D and the N in these words.
The T [t] is disappearing, too, in rapid speech. So the pronunciation of these words are reduced in fast speech to didn, wouldn, couldn. Now, we approaching the point where there is very little to distinguish did from didn’t, etc.
I suspect the pronunciation that so irritates you is spreading because it more clearly distinguishes the negative forms of these words from the positive. Also, it is possible that some young speakers of English don’t realize that these words are contractions involvingi not.
There is no right or wrong about this; it is normal cross-generational language change. It annoys me, too, but even more annoying is the misspelling it encourages: didn’t spelled diddent occurs 150,000 times on the Web.