Prescriptivism and Descriptivism

Prescriptivism:

'The attitude or belief that one variety of language is superior to others and should be promotes as such.'
Prescriptivist's believe that there are rules that define how language should be used and that mistakes are created by these rules (spelling, grammar, etc.) being broken. Prescriptive rules include:

• Don't end a sentence with a prepositions
• Don't split infinitives
• Don't use the passive voice
• Don't use the pronoun 'I' in object position

Prescriptivists:
Robert Yates Jim Kenkel

Descriptivism:

'A nonjudgmental approach to language that focuses on how it is actually spoken and written.'

Descriptivists:

Steven Pinker
David Crystal

Steven Pinker on Descriptivism vs Prescriptivism:

'According to the sadly standard dichotomy, prescriptivists believe that certain usages are inherently correct and others inherently incorrect, and that to promote correct forms is to uphold truth, morality, excellence, and a respect for the best of our civilization. To indulge incorrect ones, meanwhile, is to encourage relativism, vulgar populism, and the dumbing down of literate culture.

Descriptivists, according to this scheme, believe that norms of correctness are arbitrary shibboleths of the ruling class, designed to keep the masses in their place. Language is an organic product of human creativity, and the people should be given the freedom to write however they please.'