rationalisatio

Latin ratio meant calculation, reason, account, or plan. The verb rationalizare — to give reason to, to explain — was a late Latin formation. In early modern English, 'rationalize' meant to make rational, to bring into conformity with reason. 19th-century industrial management used 'rationalization' for reorganizing production methods on scientific principles — making the factory rational.

Ernest Jones, Freud's biographer and colleague, introduced 'rationalization' as a psychological defense mechanism in 1908. He observed that people routinely constructed plausible logical justifications for actions and beliefs that were actually driven by unconscious motives. The rationalization came after the decision — a logical veneer applied to an emotional or instinctive act.

Later psychological research validated and complicated Jones's observation. Jonathan Haidt's 'social intuitionist model' (2001) proposed that moral judgments are made intuitively and instantly, with reasoning added afterward — a process of 'post hoc rationalization.' The brain makes the decision; the reasoning faculty explains it. The explanation is sincere but comes after the fact.

Today rationalization appears in behavioral economics (the post-hoc reasons people give for consumer choices), moral psychology (the justifications for already-chosen positions), and clinical psychology (the defense against recognizing unacceptable motivations). The Latin ratio — the careful accounting — turns out to be often deployed in service of conclusions already reached.