If you were asked to prove that two and two made four, you might find some difficulty, and yet you are quite sure of the fact.
 Arthur Conan Doyle, A Study in Scarlet (1887). copy citation

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Author Arthur Conan Doyle
Source A Study in Scarlet
Topic knowledge proof facts
Date 1887
Language English
Reference
Note
Weblink http://www.gutenberg.org/files/244/244-h/244-h.htm

Context

“You broke the thread of my thoughts; but perhaps it is as well. So you actually were not able to see that that man was a sergeant of Marines?»
«No, indeed.»
«It was easier to know it than to explain why I knew it. If you were asked to prove that two and two made four, you might find some difficulty, and yet you are quite sure of the fact. Even across the street I could see a great blue anchor tattooed on the back of the fellow's hand. That smacked of the sea. He had a military carriage, however, and regulation side whiskers. There we have the marine.” source

Meaning and analysis

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