Phonemes and Allophones in Speech Analysis
W. F. Twaddell · The Journal of the Acoustical Society of America · 1952
Phonemes are quite abstract units. The criteria for establishing them are primarily distributional and articulatory, not acoustic. A unit intermediate between a single speech-event-segment and a phoneme is the allophone. An allophone is a statistical average, with constant, identifiable acoustic characterization. For many purposes of engineering, psychology, pedagogy, and information theory, the allophone may be a more suitable unit than the phoneme.