Origins
The word 'conversion' derives from Old French 'conversion,' from Latin 'conversiΕ' (a turning aroundβββββββββββββββββββββββββββββββββββββββββββββββββββββββββββββββ, a revolving, a transformation), the noun form of 'convertere' (to turn around, to transform completely). The Latin verb compounds 'con-' (an intensive prefix meaning together or completely) with 'vertere' (to turn), from Proto-Indo-European *wert- (to turn). A conversion is, at its etymological core, a complete turning β a reversal of direction, a transformation from one state to another.
Latin 'vertere' (to turn) is one of the most productive roots in the English language, generating a vast family of words that all involve some form of turning. 'Revert' is to turn back. 'Invert' is to turn inward or upside down. 'Divert' is to turn aside. 'Subvert' is to turn from below β to undermine. 'Pervert' is to turn thoroughly wrong. 'Avert' is to turn away. 'Introvert' is someone turned inward. 'Extrovert' is someone turned outward. 'Versatile' means able to turn readily from one thing to another. 'Verse' is a turning β a line of poetry that turns at the end, like a plow turning at the end of a furrow (Latin 'versus,' a furrow, a line of writing). 'Version' is a turning of a text β a different form of the same work. 'Vertebra' is a bone that turns β the jointed segments of the spine that allow the body to bend and rotate.
In Classical Latin, 'conversiΕ' was primarily physical: the turning of a wheel, the revolution of a celestial body, the about-face of a marching soldier. But early Christian writers transformed the word into one of the most powerful concepts in Western religious thought. 'ConversiΕ' became the soul's turning β the moment when a person turns away from sin and toward God. St. Augustine's Confessions (c. 397 CE) describes his own 'conversiΕ' as a dramatic turning point: the moment in the garden when he heard the voice saying 'tolle lege' (take and read) and turned from his former life to Christianity.
Development
This religious sense dominated the word for over a millennium. To convert was to turn to the true faith; conversion was the turning itself. Forced conversions β of Jews and Muslims in medieval Spain, of indigenous peoples in the Americas β were justified by the theology that any turning to the true God was good, regardless of the circumstances. The violence embedded in the history of 'conversion' is inseparable from the word's spiritual meaning.
The secular senses of 'conversion' expanded steadily from the seventeenth century onward. Currency conversion (turning one form of money into another), unit conversion (turning one measurement into another), and industrial conversion (turning raw materials into finished products) all preserve the turning metaphor. In football, a conversion is the play that 'turns' a touchdown into additional points. In real estate, a conversion turns a building from one use to another (warehouse to apartments). In psychology, conversion disorder is a condition where emotional distress 'turns into' physical symptoms β the body expresses what the mind cannot.
The digital age introduced conversion rate β the percentage of website visitors who 'turn' from browsers into buyers. This marketing term brings the word full circle: like the medieval missionary, the modern marketer seeks to produce conversions β to turn the uncommitted into the committed, the indifferent into the engaged.