1 · The story
In this lesson: Meet the root act (do, drive), spot its variant ag, and read 8 everyday words through it.
The story
The root act comes from Latin agere, one of the busiest verbs in the entire language. Agere meant "to do, to drive, to set in motion" — the same word a Roman farmer used for driving cattle, a general for leading an army, and a lawyer for pleading a case. Latin verbs leave behind two stems: the present stem (ag-, seen in agere) and the past-participle stem (act-, from actus, "done, driven"). English inherited both, and act- became the more visible of the two.
From actus came the simplest words first: act (a thing done, or to do something) and action (the doing itself). Add a suffix and you get the people and qualities: an actor acts, an activist acts on convictions, activity is the state of acting, and to activate is to make something start acting.
The real power of act shows up when prefixes give the action a direction:
- re- (back) + act → react: act back at something — a response
- inter- (between) + act → interact: act between each other
- counter- (against) + act → counteract: act against, to cancel out
- en- (make) + act → enact: make something into action — pass a law
- trans- (across) + act → transaction: business carried across between two parties
- retro- (backward) + active → retroactive: an action reaching backward in time
One member hides its origin completely: exact comes from ex- (out) + agere — literally "to drive out" or "weigh out." A Roman tax collector exacted payment by driving it out of you, and to weigh something out precisely is to be exact. The "precise" meaning and the "demand forcibly" meaning are two faces of the same act of driving something out to the exact amount.
Notice the pattern: act stays constant as the core idea of doing, and the prefix tells you which way the doing points — back (react), between (interact), against (counteract), or out (exact). The twin stem ag- (agent, agenda, agile) carries the same verb in its present form; the two are really one Latin word wearing two coats.
2 · The family
Focus words· 8
act + -ive (tending to act) + -ity (state) = the state of acting, or a thing one does. Two everyday senses split from this: countable 'an activity' (a pursuit) and uncountable 'activity' (busyness).
The club offers activities for all ages.
There was a lot of activity in the office before the deadline.
From actual ('existing in act/fact') + -ly. Originally 'in deed,' it now flags the real state of things — often to correct an assumption ('Actually, it's free').
I thought it was hard, but it was actually quite easy.
Actually, the meeting starts at three, not two.
act (do, drive) + -ive (tending to) = 'tending to do, full of doing.' A person who keeps doing things is active (energetic); a system that is doing its job right now is active (operating); someone who acts rather than waits is active (taking initiative). In grammar, the active voice is the one where the subject does the action — 'The dog bit the man,' not 'The man was bitten.'
He stays active by cycling to work every day.
Your account is still active, so you can log in anytime.
In active and activity, the root act means…
act (do, perform) + -or (one who does) = literally 'one who acts.' On stage that means someone who performs a part; in everyday and formal use it keeps the plain sense of 'one who acts' — any party that takes action, such as a 'key actor in the negotiations.'
She is a talented actor who has won several major awards.
Each country is an actor on the international stage.
re- (back) + act (do) = to act back. Something happens to you, and you act back at it — that's a reaction. The chemistry sense is the same image made literal: two substances act on each other and change.
re- (back) + act = to act back. Whatever hits you, you act back at it — that's a reaction. The word lives a double life: in everyday English it's emotional or social (react to bad news), while in chemistry it's literal (two substances react). Both come from the same image: something pushes, and something pushes back.
How did she react when you told her the news?
Don't react so strongly to every little criticism.
ex- (out) + agere/actus (drive, weigh) = 'to drive out, weigh out.' A Roman tax collector exacted payment by driving it out of you — hence the verb 'demand forcibly.' To weigh something out to the precise amount gave the adjective: exact, accurate to the last grain. The 'precise' and 'demand' meanings are two faces of one act of driving out.
exact is a surprise member of the act family — most people never connect 'precise' with 'driving out.' But both senses come from ex- + agere: to drive something out to the exact measure. The accountant's 'exact figure' and the tyrant who 'exacts tribute' are doing the same Latin action.
The surprise member. exact = ex- (out) + agere (drive) = 'to drive out, weigh out.' A Roman tax man 'exacted' money by driving it out of you (the verb: to demand forcibly). Weighing something out to the precise amount gave the adjective: exact, accurate to the last grain. Same act of driving-out, two meanings.
Can you tell me the exact time of the meeting?
These are his exact words.
re- (back) + act (do) → "do something back in response." Which word is it?
ag (drive/do) + -ent (one who) = the doer, the active party. An agent is whoever or whatever does the acting: a person acting for you (real-estate agent), a person acting secretly (secret agent), or a substance that makes something happen (cleaning agent). The thread is always 'the active cause.'
Her agent negotiated the book deal.
He turned out to be a foreign agent.
agent + -cy (state/office) = the office of an agent, or the power of acting. Two senses: the organization that acts for you (travel agency), and the philosophical 'agency' — your capacity to act for yourself.
She works for an advertising agency.
The reform gave workers more agency over their schedules.
Extended family · 40 words
See the root page for the full family.
Coach note
act and ag are the same root in two spellings — ag shows up before -ent/-ency, as in agent and agency. When you see either, think "someone is doing something."
Related Roots
3 · The quiz
Practice
What does the root act mean?