# Imaginary
## Overview
**Imaginary** means existing only in the mind — not real, not actual. The word operates across everyday language ('an imaginary friend'), literature ('an imaginary world'), and mathematics ('imaginary numbers'), with the mathematical sense carrying a history of its own.
## Etymology
From Latin *imaginarius* ('of images, existing in imagination'), from *imago* (genitive *imaginis*) meaning 'image, likeness, representation, copy.' The Latin noun is likely related to *imitari* ('to copy, imitate'), both possibly from PIE **\*h₂eym-** ('copy, image').
## Roman Imagines
In Roman culture, *imagines* (plural of *imago*) were wax portrait masks of deceased ancestors, kept in wooden cabinets in the atrium of aristocratic homes. During funeral processions, living relatives wore these masks, literally embodying the dead. The right to display *imagines* (*ius imaginum*) was a marker of noble status — only families whose members had held high office possessed them.
This practice gives the word *imago* a concreteness that its English descendants have largely lost. An image was first a physical object — a mask, a portrait, a likeness cast in wax or painted on wood — before it became a mental picture.
## From Physical to Mental
The semantic expansion from 'physical likeness' to 'mental picture' occurred in Latin itself. Cicero used *imago* for both portrait and mental impression. By the time English borrowed the vocabulary in the 14th century, the abstract sense was well established. English **image** can mean a photograph, a
**Imagination** — the faculty of forming mental images — enters English in the same period, carrying the full philosophical weight of medieval and Renaissance debates about whether imagined things have any reality.
## Imaginary Numbers
René Descartes introduced the term *imaginaire* ('imaginary') in his *La Géométrie* (1637) to describe numbers involving the square root of negative quantities. He meant it dismissively — these numbers seemed to him fictional, impossible, mere artifacts of algebraic manipulation.
Leonhard Euler formalized the notation in the 18th century, assigning the symbol *i* to √(-1). Over the following centuries, imaginary numbers proved indispensable in mathematics, physics, and engineering. They are essential for describing wave behavior, alternating electrical current, quantum mechanical states, and signal processing. The 'imaginary' label persists as a historical artifact — a reminder
## The Imago/Imitari Connection
Latin *imago* ('image') and *imitari* ('to imitate') are likely from the same PIE source. The connection is semantic as well as etymological: an image is a copy, and to imitate is to produce a copy. English inherits both branches: **image/imagine/imaginary** from *imago*, and **imitate/imitation** from *imitari*.
## Related Forms
The word family includes **image** (noun), **imagine** (verb), **imagination** (the faculty), **imaginative** (possessing imagination), **imaginary** (not real), and **imagery** (images collectively, especially in literature). The psychological term **imago** (an idealized mental image of a parent, coined by Jung) borrows the Latin word directly.