agēns

Agent comes from the Latin agēns (doing, acting), the present participle of agere (to do, to drive, to lead). The word entered English in the late fifteenth century from Medieval Latin agēns, initially meaning 'one who acts on behalf of another.' The legal, commercial, and diplomatic meanings appeared almost simultaneously — an agent was anyone authorized to act in someone else's name.

The Latin root agere generated one of the largest word families in English. Agenda (things to be done). Agile (able to move). Agitate (to drive into motion). Navigate (to drive a ship). Mitigate (to make mild). Prodigal (driving forth wealth). Cogent (driving together into a point). The word agent is the most direct descendant — the person who does.

The word's range expanded in the twentieth century. Intelligence agents (spies). Chemical agents (substances that cause reactions). Literary agents (people who sell manuscripts). Real estate agents (people who sell houses). Travel agents (people who arrange journeys). In each case, the core meaning persists: an agent causes something to happen that would not happen without them.

The philosophical meaning — agency, the capacity to act — emerged in the twentieth century. 'She has agency' means she has the power to make choices and take actions. The Latin root that meant 'to drive a chariot' became the word for human autonomy. The distance between driving a horse and driving your own destiny is bridged by a single verb.