Which 1919 book by H. L. Mencken studies English as used in the United States?

The 1919 book by H. L. Mencken that studies English as used in the United States is The American Language.

Mencken’s full title was The American Language: An Inquiry into the Development of English in the United States. The book examined American vocabulary, pronunciation, slang, names, and expressions, treating them as evidence of a developing national variety rather than simply as errors against British standards.

Mencken drew inspiration from American speech, including language he heard in Baltimore and Washington, and from writers such as Mark Twain. He challenged prescriptive critics who condemned “Americanisms,” arguing that living languages change through everyday use rather than remaining fixed by schoolbooks.

The work became unusually successful for a reference book and was revised several times. A fourth, expanded edition appeared in 1936, followed by substantial supplements in 1945 and 1948. It is often confused with general usage manuals such as Modern English Usage, but Mencken’s subject was specifically the historical development of English in the United States.