The well known phrase “Elementary, my dear Watson”, was never actually said by the Sherlock Holmes character in any of Sir Arthur Conan Doyle’s written works. “Elementary,” and “…my dear Watson.” both do appear near the beginning of The Crooked Man (1893), it is the “…my dear Watson” that appears first, and “Elementary”is the succinct reply to Watson’s exclamation a few lines of dialogue later. This is the closest these four immortal words ever appear together in the work.
The first documented occurrence of this quote appears in the P. G. Wodehouse novel, “Psmith, Journalist”, which was serialized in The Captain magazine (1909-10) then published in book form (1915) and contains the following dialog:
“That’s right,” said Billy Windsor. “Of course.”
“Elementary, my dear Watson, elementary,” murmured Psmith.
It also appears at the very end of the 1929 film, The Return of Sherlock Holmes, the first Sherlock Holmes sound film. The phrase might owe its household familiarity to its use in Edith Meiser’s scripts for The New Adventures of Sherlock Holmes radio series, broadcast from 1939 to 1947. (wiki-quotes, wikipedia, toonpool.com -image)