However, the "correction" of English grammar was not a large subject of formal study until the 18th century. Poet John Dryden remarked that the grammar in use in his day (second half of the 1600s) was an improvement over the usage of William Shakespeare. Dryden was himself the first to promulgate the rule that a sentence must not end with a preposition. Samuel Johnson's 1755 dictionary contributed to the standardization of English spelling. More influentially, the first of a long line of prescriptionist usage commentators, Robert Lowth, published "A Short Introduction to English Grammar" in 1762. Lowth's grammar is the source of many of the prescriptive shibboleths that are studied in schools and was the first of a long line of usage commentators to judge the language in addition to describing it. For example, the following footnote from his grammar is, in turn, descriptive and prescriptive: ""Whose" is by some authors made the Possessive Case of "which", and applied to things as well as persons; I think, improperly."