Main trends in phoneme theory

Mentalist (Psychological) View
I.A. Baudouin de Courtenay, L.V. Shcherba, E.D. Sapir, A. Sommerfelt, N. Chomsky, M. Tatham
Phoneme – an ideal mental image
Exist in mind but not in reality
Speech sounds (allophones) are an imperfect and varying realization of a phoneme

De Saussure’s Theory
A phoneme is defined by its features which differ its acoustic image from other phonemes