How many vowels are there in Lhasa Tibetan?

Lhasa Tibetan is described in a number of independent research traditions which give different accounts of its phonology. To what extent do these discrepancies reflect real dialectal or idiolectal differences? To what extent do they reflect different analyses of the same system? In this paper, we examine one aspect of Lhasa Tibetan phonology on which different descriptions show substantial discrepancies: vowels. Different descriptions of Lhasa Tibetan transcribe from 8 to more than 16 vowel qualities, ascribing to them different degrees of phonemicity. A detailed comparison of the transcription systems shows that all reflect the same underlying system of 12 vowel sounds, which agrees with the transcription conventions of the Seattle Tibetanists. The discrepancies among the systems mostly concern four vowels, namely ɔ, ə, ɪ and ʊ. These vowels, which started as allophonic variants of other vowels, later appear in a set of words which cannot be explained as allophony, and hence are unambiguous phonemes in contemporary Lhasa Tibetan.