It has been suggested that there is not really a contrast between ə and Λ, since a only occurs in weak syllables and no minimal pairs can be found to show a clear contrast between ə and Λ in unstressed syllables (although there have been some ingenious attempts). This has resulted in a proposal that the phoneme symbol ə should be used for representing any occurrence of ə or Λ, so that 'cup' (which is usually stressed) would be transcribed 'kəp and 'upper' (with stress on the initial syllable) as 'əpə. This new ə phoneme would thus have two allophones, one being ɔ and the other Λ; the stress mark would indicate the Λ allophone and in weak syllables with no stress it would be more likely that the ə allophone would be pronounced.

Other phonologists have suggested that ə is an allophone of several other vowels; for example, compare the middle two syllables in the words 'economy' ɪ'kɒnəmi and 'economic' i:kə'nɒmɪk - it appears that when the stress moves away from the syllable containing ɒ the vowel becomes ə. Similarly, compare 'Germanic' ʤз:'mænɪk with 'German' ' ʤз:mən - when the stress is taken away from the syllable mæn, the vowel weakens to ə. Many similar examples could be constructed with other vowels; some possibilities may be suggested by the list of words, to show the different spellings that can be pronounced with ə. The conclusion that could be drawn from this argument is that a is not a phoneme of English, but is an allophone of several different vowel phonemes when those phonemes occur in an unstressed syllable. The argument is in some ways quite an attractive one, but since it leads to a rather complex and abstract phonemic analysis it is not adopted for this course.