I was always taught that the most straightforward way to write American diphthongs is [aj] and [aw], and the "long" mid vowels as [e] and [o]. It's a simplification, but every representation is a simplification, and this is the appropriate level of detail for dictionary transcriptions, ESL texts and introductory linguistics.
Recently I've been seeing [ɑɪ ɑʊ ɛɪ] and [ɔʊ] popping up. This seems to reflect at least three different changes:
1. A shift from using [j w ɰ] to represent glides, to representing diphthongs as a series of vowel sounds.
2. A shift to greater detail in these representations.
3. A shift in the standard from somewhere close to my dialect (Hudson Valley) to ... someplace else.
When it was just on dictionary.com (credited to Random House and Collins) I thought it was just one editor's quirk, but it's in the ESL text I'm using this semester (Grant 2010), and now in the new edition of Yule's Study of Language (2010), and Language Files (2007). What gives? Does anyone know what's going on? Did this happen gradually by people copying each other, was it argued for in a paper, or was it decided by some LSA committee that I never heard about? Is that level of detail really necessary in dictionaries, ESL texts and introductory linguistics books, and how do we know that it is?
Most importantly, where in the US do people say [ɑɪ] and [ɑʊ] but pronounce their /o/s as [ɔʊ] and not [ɛʊ]? How did that place get to be the standard, and why didn't my fellow [ɑi] and [ɑu] speakers fight harder to get our pronunciation in there?
I hope someone out there can shed some light on this.
