Allophonic assimilation – dentalization
To reiterate, assimilation occurs when one sound is altered owing to the influence of a neighboring segment. In the previous example we saw how alveolars may be dentalized across a word boundary when followed immediately by a dental sound. A further example should serve to consolidate this concept:
|hot thing||/hɒt θɪŋ/|
In the phrase hot thing the word boundary occurs between the first word hot and the immediately following word thing. The first word hot ends with the alveolar sound /t/. This sound, therefore, precedes the word boundary. The first sound following the word boundary is the dental consonant /θ/ in the word thing. The alveolar sound before the word boundary is, consequently, dentalized in anticipation of the upcoming dental sound that occurs immediately after the word boundary, i.e.
|hot thing||/hɒt θɪŋ/||→||[hɒt̪ θɪ̃ŋ]|
Note that in this example the dentalized [t̪] is produced without aspiration as it is unreleased. That is to say, the oral cavity is occluded to create the stop consonant but there is no audible release in the plosive phase of its production. Unreleased plosives are marked in IPA with the diacritic [ ̚], i.e.
|hot thing||/hɒt θɪŋ/||→||[hɒt̪̚ θɪ̃ŋ]|
Further examples of dentalization across word boundaries include the following.
|hit this||/hɪt ðɪs/||→||[hɪt̪̚ ðɪs]|
|ten things||/tɛn θɪŋz/||→||[tɛ̃n̪ θɪ̃ŋz̥]|
|tell that||/tɛl ðæt/||→||[tɛl̪ ðæʔ]|
In summary, we see that as well as dentalization occurring within words, this process can also operate in connected speech across word boundaries. The above examples demonstrate how alveolars before a word boundary are dentalized if the initial sound of the next word is a dental. Under these circumstances, the alveolar assimilates the place of articulation of the dental. We can summarize this into a rule about dentalization across word boundaries:
The brown vertical line represents a word boundary and the rule is read as:
‘If the sound in word-final position of the word preceding the word boundary is an alveolar /t, d, n, s, z, l/ and if the sound in word-initial position in the word immediately following the word boundary is a dental /θ, ð/ then the alveolar is dentalized.’
Some further examples should make this clear:
|can they?||/kæn ðeɪ/||→||[k̟ʰæ̃n̪ ðeɪː]|
|this thing||/ðɪs θɪŋ/||→||[ðɪs̪ θɪ̃ŋ]|
|those things||/ðəʊz θɪŋz/||→||[ðəʊːz̪̊ θɪ̃ŋz̥]|
|all those||/ɔɫ ðəʊz/||→||[ɔːɫ̪ ðəʊːz̥]|
Each instance is an example of allophonic assimilation because the newly assimilated sound is an allophone of the transformed phoneme. This process of allophonic assimilation can be summarized in the following statement.
Word-final alveolars are dentalized before dental fricatives.
As well as dentalization, the assimilatory process of labialization can also occur across word boundaries.