In addition to dictionaries, many English grammars started to appear in the 18th Century, the best-known and most influential of which were Robert Lowth's “A Short Introduction to English Grammar” (1762) and Lindley Murray's “English Grammar” (1794). In fact, some 200 works on grammar and rhetoric were published between 1750 and 1800, and no less than 800 during the 19th Century. Most of these works, Lowth’s in particular, were extremely prescriptive, stating in no uncertain terms the “correct” way of using English. Lowth was the main source of such "correct" grammar rules as a double negative always yields a positive, never end a sentence with a preposition and never split an infinitive.