经验证据表明,一个言语集团中系统性最强、最能清楚地显示语言发展进程的音系是人们漫不经心交谈时用的音系,它有着最少的区别对立而有着最多的语境支持。如纽约市内无-r的那类言语,其收音向央滑动的长元音系统,在最正式的话语中可找到例词说明它有7个对立的成员:134 Empirical evidence shows that the phonological system that is the strongest system in the language group that most clearly shows the process of language development is the system of phonetics that people use when talking casually, with the least disagreement and the highest level of contextual support. For example, in New York City, there is no such thing as -r, and its radio voice moves to the center of the long vowel system. In the most formal discourse, it can be found that it has seven opposite members: 134