Perhaps the most famous quotation attributed to Doyle's
character, Sherlock Holmes, is "Elementary, my Dear Watson." The
Oxford Dictionary of Quotations, Fourth Edition, 1992, p. 256,
states that the quotation "is not found in any book by Conan
Doyle, although a review of the film The Return of Sherlock Holmes
in the New York Times 19 October 1929. p. 22, states: 'In the final
scene Dr Watson is there with his "Amazing, Holmes," and Holmes
comes forth with his "Elementary, my dear Watson, elementary."'
Here are a few other quotations which ARE in Doyle's books:
'Excellent,' I cried. 'Elementary,' said he. (The Memoirs of
Sherlock Holmes (1894), 'The Crooked Man.')
You see, but you do not observe. (The Adventures of Sherlock
Holmes (1892) 'The Red-Headed League.')
How often have I said to you that when you have eliminated the
impossible, whatever remains, however improbable, must be the
truth? (The Sign of Four (1890) ch. 6)
It is a capital mistake to theorize before you have all the
evidence. It biases the judgment. (A Study in Scarlet (1888) ch.
3)
Where there is no imagination, there is no horror. (A Study in
Scarlet (1888) ch. 5)
Mediocrity knows nothing higher than itself, but talent
instantly recognises genius. (The Valley of Fear (1915) ch.1)