R-deletion and Schwa Insertion

In non-rhotic varieties of English, the /r/ is deleted after a vowel. However, many non-rhotic varieties of English such as Received Pronunciation also insert a schwa. This only occurs after the high front, mid front and high back lax vowels.

In words such as car and fork, English dialects such as Received Pronunciation delete the /r/ and lengthen the vowel. This is known as compensatory lengthening. However, in words with high tense vowels such as here and tour, the /r/ is deleted, the vowel becomes lax, and a schwa is inserted. With words such as there, the vowel is lax, and as a result, vowel laxing does not apply.

The schwa is inserted after three vowels which are close to the schwa with respect to tongue height and tongue backness. The lax vowels are closer to the schwa than the tense vowels. In addition, they do not lengthen. It appears that the insertion of the schwa replaces the deleted /r/.

Here is an analysis of the words here, there and tour in dialects of English with schwa insertion:

UR /hir/
r-deletion hi
schwa insertion hiɘ                 
vowel laxing hIɘ
PR [hIɘ]

UR /ðɛr/
 r-deletion ðɛ
schwa insertion ðɛɘ
vowel laxing
PR [ðɛɘ]

UR /tur/
r-deletion tu
schwa insertion tuɘ
vowel laxing tʊɘ
PR [tʊɘ]

The rules of r-deletion and schwa insertion need to be ordered. R-deletion is necessary because it is the trigger for schwa insertion. It is also necessary to apply schwa insertion before vowel laxing because lax vowels do not occur word-finally.

Non-rhotic varieties of English have compensatory lengthening after the loss of post-vocalic /r/. However, many non-rhotic varieties have schwa insertion after the high front, mid front and high back vowels. These vowels are close to the schwa in both vowel height and backness. In addition to schwa insertion, the tense vowels become lax. The lax vowels are closer to the schwa in both backness and height than are the tense vowels.