Origins
The English word 'condition' entered the language in the fourteenth century from Old French 'condicion,' itself from Latin 'condiciō.' The etymology of the Latin word reveals a concept rooted in the practice of Roman contract law: 'condiciō' derives from 'condīcere,' meaning 'to talk together' or 'to agree upon terms,' a compound of 'con-' (together) and 'dīcere' (to say, to speak, to declare).
The PIE root behind 'dīcere' is *deyḱ-, meaning 'to show' or 'to point out.' This root was enormously productive across the Indo-European languages. In Latin, it generated 'dīcere' (to say — originally to point out with words), 'dictāre' (to dictate), 'indicāre' (to indicate, to point out), 'praedīcere' (to predict, to say beforehand), 'iūdex' (judge, from *yous-dik-, one who points out the law), and 'index' (one who points out). In Greek, the same root produced 'deiknynai' (to show) and 'díkē' (justice, custom — that which is pointed out as right). In Sanskrit, it gave 'diśati' (shows, points).
The semantic journey of 'condiciō' from 'talking together' to 'the state of things' is a striking case study in meaning change. In Roman legal language, 'condiciō' initially meant the terms that parties agreed upon — the conditions of a contract, the stipulations of a treaty. From 'agreed-upon terms,' it extended to 'the terms under which something exists' — that is, the circumstances or situation of a thing. From 'circumstances,' it extended further to 'the state or quality of a thing' — a person's health condition, the condition of a building.
Latin Roots
A complication in the word's history involves two distinct Latin words that merged in medieval usage. Latin 'condiciō' (from 'condīcere,' to agree) and 'conditiō' (from 'condere,' to found, to establish) were separate words with separate meanings, but scribes frequently confused their spellings. The English spelling 'condition' with a -t- reflects the influence of 'conditiō,' even though the word's meaning comes primarily from 'condiciō.' This orthographic merger is one of the many small accidents that shaped the English lexicon.
In medieval English, 'condition' often meant 'social rank' or 'station in life' — a person's 'condition' was their place in the social hierarchy. This sense survives in phrases like 'people of every condition' and in the adjective 'conditioned' as used in 'well-conditioned' (of good character or status). The sense of physical fitness ('in good condition,' 'out of condition') is a nineteenth-century development, reflecting the era's growing preoccupation with bodily health and athletic performance.
The logical and philosophical sense of 'condition' — a prerequisite that must be met — has been central to Western thought since the Scholastic period. Philosophers distinguish between 'necessary conditions' (without which something cannot be), 'sufficient conditions' (which guarantee something will be), and 'necessary and sufficient conditions' (which both require and guarantee). This technical vocabulary pervades not only philosophy but law, science, medicine, and computer programming ('conditional statements,' 'if-then conditions').
Later History
The verb 'to condition' adds another layer. Meaning originally 'to agree upon terms' and then 'to bring into proper condition,' it acquired its psychological sense from Ivan Pavlov's work in the early twentieth century. Pavlov's 'conditioned reflex' (a response trained through repeated association) gave English 'conditioning' in the behavioral sense — a use now so common that most speakers hear 'conditioning' and think of either psychology or hair care rather than contractual stipulation.
The adjective 'unconditional' — meaning without stipulations, absolute — first appeared in the seventeenth century and became a powerful political and philosophical term. 'Unconditional surrender,' 'unconditional love,' and 'unconditional rights' all leverage the word's legal origin: to be unconditional is to transcend the realm of negotiation and agreement, to exist beyond the bargaining table where 'condiciō' was born.