Diphthongs

The three diphthongs of American English, /aɪ, aʊ, ɔɪ/, given in figure 1, can appear in all word positions, are all stressed on the first vowel, and all end in a high vowel. While the end points are pretty well established across the varieties of American English, the first element of these diphthongs may show considerable variation.

• /aɪ/: The most common beginning point for this diphthong is [a], but it may shift to a more back [ɑ]. In the southern USA, /aɪ/ becomes [ɑ:] or [a:] if not followed by a voiceless consonant (e.g. buy [bɑ:], miles [mɑ:lz]). In southern Philadelphia and parts of New York City, one hears [Λɪ] instead. In the mid land and South, it is often reduced to a monophthong before /ɹ̣/ (e.g. fire [faɹ̣]).

• /ɔɪ/: For this diphthong, the starting point is back lower-mid, and the tongue glides from /ɔ/ toward /ɪ/. The lips are slightly rounded for the first element and neutral for the second. In Pennsylvania, Maryland, and Delaware, /ɔɪ/ sometimes approximates to [oɪ]. In AAVE and in the South, we normally get a monophthongized [ɔ:] (e.g. oil [ɔ:l], foil [fɔ:l], boil [bɔ:l]). In Outer Banks islands off the coast of North Carolina, [aɪ] may be found, thus making toid and tide homophonous.

• /aʊ/: The starting point for this diphthong is normally not as front as that of /aɪ/, but not as back as that of /ɑ/, although the latter may be the case across the North from New England through the Great Lakes, and on into Minnesota. In the South, [aʊ] and [æʊ] (fronting and raising of the nucleus) are common, while in Nebraska and Iowa [æʊ] predominates. Raising the nucleus is typical in Canada (e.g. out [əʊt]). In Virginia and to some extent in northern New England, Wisconsin, and Minnesota, the allophone [Λʊ] is found before voiceless consonants (e.g. house [hΛʊs], out [Λʊt]). Along the southern coastal area, [aɪ] may be found, making down and dine homophonous [daɪn]. Monopthongization of this diphthong is found in Pittsburgh (e.g. down [da:n]).

Besides these diphthongs, in non-rhotic varieties (eastern New England, New York City, lower South), the targets with V + /ɹ̣/ turn into centering diphthongs. Thus, we have the following correspondences:

In the case of [ɑɹ̣], we get a prolonged [ɑ:] rather than [ɑə] (e.g. car [kɑ:]). The remaining three diphthongs show the following centralizations:

As we have seen, there is considerable variation in the vowels and diphthongs of American English. Most of these differences deal with the following two well-known chain shifts: Northern Cities Shift and Southern Shift. These shifts are systematic changes in vowel systems with a rotation of the entire system. That is, when a sound shifts to the place of another sound, the latter sound shifts as well in order to ensure that the two sounds remain distinct enough to convey meaning differences. The two chain shifts that are underway in American English are described below.

Northern Cities Shift is seen in western New England, New York State, northern Pennsylvania, northern Ohio, Illinois, Michigan, and Wisconsin. A more advanced form of this shift is mainly concentrated in the larger metropolitan areas (Syracuse, Buffalo, Cleveland, Toledo, Detroit, Chicago, Madison). This shift, which is a clockwise rotation, is shown in figure 2.

Six vowels, /ɔ, ɑ, æ, ε, ɪ, Λ/, are affected. The low vowels /æ/ and /ɑ/ are moved forward and/or raised, and the others are moved backward and/or lowered. /ɔ/ in thought moves down and starts to sound like the /ɑ/ of father. The /ɑ/, in turn, moves toward /æ/, thus lock starts to sound like lack. The /æ/ in man is raised and fronted to [iə] and the word sounds like [miən]. The two non-low lax front vowels /ε/ and /ɪ/ undergo a move backward (and also lower in the latter); thus, bet starts to sound like but. Finally, /Λ/ moves backward to /ɔ/, making shut sound like shot.

Southern Shift is found throughout the southern states, the Mid-Atlantic states, and the southern mountain states. This shift, besides monophthongizing /aɪ/ (e.g. five [faɪv] → [fa:v]), affects the following six vowels: /i, ɪ, e, ε, u, o/.

It rotates them as follows: front lax vowels /ɪ, ε, æ/ move upward (e.g. him [hɪm] → [him]; bed [bεd] → [bɪd]; can’t [kænt] → [kεnt]), and front tense vowels /i/ and /e/ are lowered and centralized (e.g. beet [bit] → [bɪt]; bait [bet] → [bεt]). Finally, the back tense rounded vowels /u/ and /o/ move forward (e.g. boot [but] → [bʉt]; boat [bot] → [bΛt]). Also observed are the raising of /ɔɹ̣/ to /oɹ̣/ (e.g. born [bɔɹ̣n] → [boɹ̣n]) and /ɑɹ̣/ to /ɔɹ̣/ (e.g. barn [bɑɹ̣n] → [bɔɹ̣n]). These are summarized in figure 3.