Prescriptive

In linguistics, prescriptive means laying down or prescribing rules of the language rather describing them. For example, a descriptive linguist working in English will try to describe the usage, distribution, and history of "ain't" and "h-dropping" neutrally, without judging them against other forms. A prescriptivist (one who is prescriptive) will often judge that they are inferior and recommend that they be avoided.

See also:

• Fowler's Modern English Usage
• "Politics and the English Language"
• Pleonasm
• Logorrhoea