Phonemic assimilation – post-alveolar place
If an alveolar plosive or fricative appears word-finally, and is followed immediately by the post-alveolar approximant /j/, it will assimilate this post-alveolar place of articulation as follows:
Consider the phrase:
|what you like||/wɒt ju laɪk/|
In a context such as this, the alveolar plosive /t/ at the end of the first word what is likely to assimilate the post-alveolar feature of the post-alveolar approximant /j/ that appears as the initial sound in the immediately following word you. It, therefore, becomes a post-alveolar affricate (assimilating the place of articulation of the /j/ whilst retaining its voicing and some of its plosive character):
|what you like||/wɒt ju laɪk/||→||[wɒʧ jə laɪkʰ]|
An additional possibility here, especially in rapidly articulated connected speech, is that the post-alveolar approximant /j/ may be omitted altogether, i.e.
|what you like||/wɒt ju laɪk/||→||[wɒʧ ə laɪkʰ]|
Further examples of this process include the following (the brackets around the (j) indicate that its inclusion is optional):
|what you said||/wɒt ju sɛd/||→||[wɒʧ (j)ə sɛd̥]|
|would you?||/wʊd ju/||→||[wʊʤ (j)ə↓]|
|this year||/ðɪs jɪə/||→||[ðɪʃ (j)ɪəː]|
|those years||/ðəʊz jɪəz/||→||[ðəʊːʒ (j)ɪəːz̥]|
We can state this rule as:
Word-final /t, d, s, z/ become post-alveolar before the post-alveolar approximant /j/, with possible disappearance of /j/.
In addition to the alveolar fricatives /s/ and /z/ becoming post-alveolar before /j/, they can also become post-alveolar before post-alveolar fricatives. However, recall that the voiced post-alveolar fricative /ʒ/ predominantly occurs between vowels and that there are very few words in English that have /ʒ/ in syllable-initial position. For the most part, therefore, /s/ and /z/ become post-alveolar when they occur before the voiceless post-alveolar fricative /ʃ/, which frequently occurs in syllable-initial position. This is summarized as follows:
|this shop||/ðɪs ʃɒp/||→||[ðɪʃ ʃɒpʰ]|
|those shoes||/ðəʊz ʃuz/||→||[ðəʊːʒ̊ ʃuːz̥]|
So, the complete rule for the assimilation of the alveolar fricatives to post-alveolars would be written as:
The following statement sums this up.
Word-final /s, z/ become post-alveolar before the voiceless post-alveolar fricative / ʃ/ and the post-alveolar approximant /j/, with possible disappearance of /j/.
 The substitution of the vowel /u/ in the word you with the neutral vowel [ə] is another example of vowel reduction which will be discussed later in this Section.
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