Intervocalic alveolar flapping

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"Flapping" redirects here. For other uses of the term, see Flap.

Intervocalic alveolar flapping (more accurately 'tapping', see below) is a phonological process found in many dialects of English, especially North American English, by which prevocalic (preceding a vowel) /t/ and /d/ surface as the alveolar tap [ɾ] after sonorants other than /ŋ/, /m/, and (in some environments) /l/.

after vowel: butter
after r: barter
after l: faculty (but not immediately post-tonic: alter --> al[tʰ]er, not *al[ɾ]er)

The term "flap" is often used as a synonym for the term "tap", but the two can be distinguished phonetically. A flap involves a rapid movement of the tongue tip from a retracted vertical position to a (more or less) horizontal position, during which the tongue tip brushes the alveolar ridge. A tap involves a rapid backwards and forwards movement of the tongue tip. The sound referred to here is the alveolar tap [ɾ], not the flap [ɽ], and hence "tapping" is the correct term from a phonetic point of view (see also Flap consonant). The term "flapping" is, however, ingrained in much of the phonological literature, so it is retained here.^[1] However, no languages are known to contrast taps and flaps in the first place.

Flapping/tapping is a specific type of lenition, specifically intervocalic weakening. For people with the merger these following words sound the same or almost the same:

betting/bedding
boating/boding
coating/coding
grater/grader
hearty/hardy
kitty/kiddie
liter/leader
latter/ladder
matter/madder
metal/medal
Patty/Paddy
rater/raider
shutter/shudder
waiter/wader

For most (but not all) speakers the merger does not occur when an intervocalic /t/ or /d/ is followed by a syllabic 'n', so written and ridden remain distinct. A non-negligible number of speakers (including pockets in the Boston area) lack the rule that glottalizes t and d before syllabic n, and therefore flap/tap /t/ and /d/ in this environment. Pairs like potent : impotent, with the former having a preglottalized unreleased t or a glottal stop (but not a flap/tap) and the latter having either an aspirated t or a flap/tap, suggest that the level of stress on the preceding vowel may play a role in the applicability of glottalization and flapping/tapping before syllabic n. Some speakers in the Pacific Northwest turn /t/ into a flap but not /d/, so "writer" and "rider" remain distinct even though the long "i" is pronounced the same in both words.

Flapping/tapping does not occur in most dialects when the /t/ or /d/ immediately precedes a stressed vowel, as in retail, but can flap/tap in this environment when it spans a word boundary, as in "got it" --> [gɑɾɪt], and when a word boundary is embedded within a word, as in "buttinsky". Australian English also flaps/taps word-internally before a stressed vowel in words like "fourteen".

In many accents, such words as riding and writing continue to be distinguished by the preceding vowel: though the consonant distinction is neutralized, the underlying voice distinction continues to select the allophone of the /aɪ/ phoneme preceding it. Thus for many North Americans, riding is [ɹɑɪɾɪŋ] while writing is [ɹɐɪɾɪŋ]. Vowel duration may also be different, with a longer vowel before tap realisations of /d/ than before tap realisations of /t/. At the phonetic level, the contrast between /t/ and /d/ may be maintained by these non-local cues, though as the cues are quite subtle, they may not be acquired/perceived by others. A merger of /t, d/ can then be said to have occurred.

The cluster [nt] can also be flapped/tapped; the IPA symbol for a nasal tap is [ɾ̃]. As a result, in quick speech, words like winner and winter can become homophonous. Flapping/tapping does not occur for most speakers in words like 'carpenter' and 'ninety', which instead surface with [d].^[2]

A similar process also occurs in other languages, such as Western Apache (and other Southern Athabaskan languages). In Western Apache, intervocalic /t/ similarly is realized as [ɾ] in intervocalic position. This process occurs even over word boundaries. However, tapping is blocked when /t/ is the initial consonant of a stem (in other words tapping occurs only when /t/ is stem-internal or in a prefix). Unlike English, tapping is not affected by suprasegmentals (in other words stress or tone).