3.3 Discovering phonemes

　 A rule of thumb to tell segments that are separate phonemes from segments that are allophones is to observe their distribution. The phonetic context (what sound precedes and what sound follows) in which a sound appears in speech is called its environment. The distribution of sounds falls into three types, each of which is the basis for judging whether the sounds distinguish meaning.

　3.3.1 Contrastive distribution
　3.3.2 Complimentary distribution
　3.3.3 Free Variation
　3.3.4 The discovery procedure