Tenses in English Grammar

Grammars evolve through usage and also due to separations of the human population. With the advent of written representations, formal rules about language usage tend to appear also. Formal grammars are codifications of usage that are developed by repeated documentation over time, and by observation as well. As the rules become established and developed, the prescriptive concept of grammatical correctness can arise. This often creates a discrepancy between contemporary usage and that which has been accepted, over time, as being correct. Linguists tend to believe that prescriptive grammars do not have any justification beyond their authors' aesthetic tastes; however, prescriptions are considered in sociolinguistics as part of the explanation for why some people say "I didn't do nothing", some say "I didn't do anything", and some say one or the other depending on social context.