normative grammar
Definition -
(1) Grammatical rules proposed as a fixed standard to which language use must conform.
(2) A treatise setting out such rules.

1. A person who promotes this is called a normative grammarian.

Example -
In his A Short Introduction to English Grammar (1762), Robert Lowth strongly advises writers to avoid ending sentences with prepositions. According to Lowth:

"This is an Idiom which our language is strongly inclined to [sic]; it prevails in common conversation, and suits very well with the familiar style in writing; but the placing of the Preposition before the Relative is more graceful, as well as more perspicuous; and agrees much better with the solemn and elevated Style."

Oxford English Dictionary -
The term's first citation is from 1901:
"Normative or didactic grammar sets up a certain standard as correct."
(H. Oertel Lect. on Study of Lang. ii. 87)

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