The Art of Language Invention:

In the early 1900s, the language of America was becoming colloquial English-the language of the businessman, manager, and professional. Since college and high school education were far from universal, many people turned to correspondence education-that era's distance learning-to learn the art of speaking and writing. By the 1920s and 1930s, thousands of Americans were sending coupons from newspapers and magazines to order Sherwin Cody's 100% Self-correcting Course in the English Language, a patented mail-order course in English that was taken by over 150,000 people.