复习资料（2.7）
7、Phone, phoneme, and allophone
语音（音素）、音位、音位变体
Phone can be simply defined as the speech sounds we use when speaking a language. A phone is a phonetic unit or segment. It does not necessarily distinguish meaning.
语音是语言学研究的单位，是一个个具体的声音。语音是一个语音单位或一个切分成分，它并不一定能区分意义。
Phonology is concerned with the speech sounds which distinguish meaning. The basic unit in phonology is called phoneme, it is a unit that is of distinctive value. But it is an abstract unit. A phoneme is not a sound, it is a collection of distinctive phonetic features.
音位是音系学研究的单位，是抽象的概念，每一个音位是一组语音特征的集合体，音位具有区别意义的作用。一个音位在语音上被具体体现为一个特定的语音（音素）。
按照惯例，音位被置于两斜线之间，如/p/ /t/，而语音被置于方括号内，如[p] [t].
The different phones which can represent a phoneme in different phonetic environments are called the allophones of that phoneme.
音位变体是一个音位在特定的语音环境里的具体体现，同一个音位在不同的语音环境里体现为不同的变体，也就是语音。