Holmesian deduction Sherlock Holmes

poster 1900 play sherlock holmes conan doyle , actor william gillette

holmes s primary intellectual detection method abductive reasoning. holmesian deduction consists of observation-based inferences, such study of cigar ashes. drop of water , writes, logician infer possibility of atlantic or niagara without having seen or heard of 1 or other .

in scandal in bohemia , holmes deduces watson had gotten wet lately , had clumsy , careless servant girl . when watson asks how holmes knows this, detective answers:

it simplicity itself ... eyes tell me on inside of left shoe, firelight strikes it, leather scored 6 parallel cuts. have been caused has carelessly scraped round edges of sole in order remove crusted mud it. hence, see, double deduction had been out in vile weather, , had particularly malignant boot-slitting specimen of london slavey.

in first holmes story, study in scarlet, dr. watson compares holmes c. auguste dupin, edgar allan poe s fictional detective, employed similar methodology. holmes replies: in opinion, dupin inferior fellow... had analytical genius, no doubt; no means such phenomenon poe appears imagine . alluding episode in murders in rue morgue , dupin deduces friend thinking despite having walked in silence quarter of hour, holmes remarks: trick of breaking in on friend s thoughts apropos remark... showy , superficial . nevertheless, holmes later performs same trick on watson in adventure of cardboard box .

deductive reasoning allows holmes learn stranger s occupation, such retired marine sergeant in study in scarlet; ship s-carpenter-turned-pawnbroker in red-headed league , , billiard-marker , retired artillery non-commissioned officer in adventure of greek interpreter . studying inanimate objects, makes deductions owners (watson s pocket watch in sign of 4 , hat, pipe, , walking stick in other stories). detective s guiding principle, says in sign of 4 , elsewhere in stories, is: when have eliminated impossible, whatever remains, improbable, must truth .

conan doyle paint holmes fallible (this being central theme of adventure of yellow face ).