Likewise, a principle of cooperation is to be presupposed as the basis of conversation. Contextual or shared knowledge among co-speakers makes it possible to derive implicatures. The definition of what standard English is meant to be is somewhat problematic. Languages, the author emphasizes, are not static objects, but fluctuate according to several variables. Therefore standard English is often considered the set of correct pronunciation, grammatical, and lexical choices.
Someone regards standard English as the most efficient and convenient variety for any occasion.
The criterion used to verify whether two varieties are the same language or not is the mutual intelligibility of their speakers. Hence phonological, grammatical, and lexical variations are of no consequence provided that people understand each other. This does not necessarily mean that each variety has the same social repute. Some sociolects are in fact viewed more favorably than others because of the cultural background they presuppose. It is here that Andrews comes back to some historical-linguistic considerations and explains the composite nature of American English vocabulary, noticing that changes are often driven by cultural attitudes and fashion more than by real needs.