Flesch’s preference for standards based in usage rather than grammarians’ prescriptions reflected the Jeffersonian view of language change as progress, a view that had earlier taken on new life as professional American linguists and English-language educators gained influence. In 1908, Yale English professor Thomas Lounsbury published The Standard of Usage in English—which comprised essays he had written for Harper’s Magazine and expanded for this volume—in which he advocated following the usage of the best speakers rather than, as he writes in the fifth of the nine essays, “school mastering the speech.” In his A Comprehensive Guide to Good English, Columbia English professor George Philip Krapp included an appendix of grammatical rules listing right and wrong usages, but most of his guide is a dictionary of unfamiliar terms—colloquial, foreign, and classical words along with place-names. To spark reflection on language, Krapp combined observations on standard usages with exploration of the folkways of American speech, and among the entries are “skidoo,” “towards,” “em” (for “them”), “hep,” and “girl.”
As the 20th century progressed, more flexible, tolerant approaches to usage gained traction. Sterling Leonard examined and debunked many 18th-century attitudes about usage in The Doctrine of Correctness in English Usage, 1700–1800. Leonard’s next book was Current English Usage (published posthumously in 1932, a year after his death), in which he asked language experts—editors, authors, linguists, businesspeople, English and speech teachers—to categorize usages as “literary English,” “standard cultivated colloquial English,” or “vulgar English” (the jury disagreed in more than half the cases it considered). Albert Marckwardt and Fred Wolcott’s Facts about Current English Usage complemented Leonard’s study by discussing that work and by examining usage comments of reference works—primarily in the recently completed OED and in Webster’s New International Dictionary of the English Language (“Webster’s Second”), edited by William Allan Neilson and Thomas Knott—to classify usage in three categories: “established,” “disputed,” and “illiterate.”
Outside the profession of English teaching, H. L. Mencken was a strong advocate of colloquial usage. From its first edition in 1919 to the enlarged fourth edition with its two supplements, Mencken’s The American Language defended American usage against British criticism, promoted the vitality of slang, and chided advocates of what he called the “schoolmarm” tradition (Lounsbury’s “school master,” now feminized). The extensive List of Words and Phrases in this book provides access to scholarly and popular commentary on hundreds of expressions.
The Standard of Usage in English by 
American Language by