Phonetic patterns allow for intelligibility tolerance because

The emergence of a standard dialect produces the phenomenon known as ‘accent’ which is quite different from dialect. In the process of learning a foreign language, it is normal to transfer the patterns of an indigenous language to those of a foreign language. With time, however, those of form and most of orthography and phonology gradually get eliminated. This is because these can easily be identified and corrected. They are easy to correct because they do not involve patterns of muscular movement. It is necessary to correct them because otherwise, they could seriously impair intelligibility.

With phonetic patterns, on the other hand, there is a great deal of intelligibility tolerance because muscular patterns are involved thus making correction difficult when observed. Besides, phonetic patterns do not impair intelligibility much. Hence the transference of phonetic habits from one language to another is both easier to tolerate and more difficult to avoid than transference at the lexico-grammatical level. It follows that a speaker who is learning a second dialect does so with an accent since the muscles of his speech organs would have crystallised in response to the phonetics of his native language which he learnt first. The speaker therefore speaks the second dialect with the phonetic features of his native dialect. The learning of a standard language is simply the learning of a second dialect- that which has been standardised.

Members of a language community control at least two dialects and use both dialects in different situations. In the rural areas, the native dialect is used in most situations since there is less movement. Therefore, rural dwellers tend to be parochial and maintain the homogeneity of their dialect. In the urban community, on the other hand, there is more demand on the standard dialect than on the rural one. This is because people from different regions converge here. In order to ensure mutual intelligibility resulting from the pressure of communication, a great deal of demand is made on the standard dialect which now becomes the lingua franca amongst them.