The occurrence of a phoneme represents the occurrence of some member of its class of segments, each member being environmentally defined. Whenever the phoneme appears we can always tell from the environment which segment member of the phoneme would occur in that position (i.e. we can always pronounce phonemic writing). Conversely since complete overlapping is avoided […], whenever we are given a segment in an environment we can always tell in which phoneme it is included (i.e. we can always write phonemically whatever we hear).
- Harris (1951), Pag. 72