Reason was a logical method of decision making. As the Twelfth Doctor told Bill Potts to remember, "Passion fights, but reason wins." He suggested that diplomacy and tact were greater tools towards solving a problem than anger and outrage. (TV: Thin Ice)

Borusa wrote a paper on the topic of reason, which the Doctor had read. When Rodan told her that it suggested the Fourth Doctor was a traitor, Leela replied that "reason [was] a liar". (TV: The Invasion of Time)

The Twelfth Doctor suggested more than once that instead of steering the TARDIS, he had to reason with it, (TV: Smile) "unsuccessfully most of the time". (TV: Thin Ice)

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