ratiocination

Edgar Allan Poe is said to have called the 1841 story The Murders in the Rue Morgue his first "tale of ratiocination." Many today agree with his assessment and consider that Poe classic to be the world's first detective story. Poe didn't actually use "ratiocination" in Rue Morgue, but the term does appear three times in its 1842 sequel, The Mystery of Marie Roget. In Marie Roget, the author proved his reasoning ability ("ratiocination" traces to "ratio," Latin for reason or "computation"). The second tale is based on an actual murder, and as the case unfolded after the publication of Poe's work, it became clear that his fictional detective had done an amazing job of reasoning through the crime.