Inductive and deductive reasoning

Integrating insights from philosophy, psychology, and neuroscience

Authored by: Vinod Goel , Randall Waechter

The Routledge International Handbook of Thinking and Reasoning

Print publication date:  November  2017
Online publication date:  November  2017

Print ISBN: 9781138849303
eBook ISBN: 9781315725697
Adobe ISBN:


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Reasoning is the process of evaluating given information and reaching conclusions that are not explicitly stated. Here is literature’s most celebrated reasoner (Arthur Conan Doyle’s Sherlock Holmes) impressing his friend Watson (in “A Scandal in Bohemia”):

Then he stood before the fire, and looked me over in his singular introspective fashion.

“Wedlock suits you,” he remarked… . “And in practice again, I observe. You did not tell me that you intended to go into harness.”

“Then how do you know?”

“I see it, I deduce it. How do I know that you have been getting yourself very wet lately, and that you have a most clumsy and careless servant girl?”

“It is simplicity itself,” said he; “my eyes tell me that on the inside of your left shoe, just where the firelight strikes it, the leather is scored by six almost parallel cuts. Obviously they have been caused by someone who has very carelessly scraped round the edges of the sole in order to remove crusted mud from it. Hence, you see, my double deduction that you had been out in vile weather, and that you had a particularly malignant boot-slicking specimen of the London slavery. As to your practice, if a gentleman walks into my room, smelling of iodoform, with a black mark of nitrate of silver upon his right fore-finger, and a bulge on the side of his top-hat to show where he has secreted his stethoscope, I must be dull indeed if I do not pronounce him to be an active member of the medical profession.”

(Doyle, 1892) More mundane examples include the following: upon being told that George is a bachelor, one automatically infers that George is not married. Or upon learning that Linda will not come to our barbecue if it rains on Saturday, and noting that it is indeed raining on Saturday, we do not set a place for her. While not as impressive as Holmes’ conclusions, they emerge in a straightforward way from the provided information, and have a certainty lacking in Holmes’ inferences.

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