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'Ago' measures time from the present moment backward; 'before' expresses time relative to another reference point.
Side-by-side comparison
"Ago" always counts backward from the moment you are speaking. Use it with the simple past and after the time expression: "two years ago", "ten minutes ago".
She graduated three years ago and has been working in marketing since then.
The project started six months ago but has already exceeded expectations.
I called him two hours ago but he has not called back yet.
"Before" does not start from the present: it expresses that something happened before another moment or event. That reference point can be in the past, present, or future.
She had never lived alone before moving to the city for her new job.
He read every page of the contract carefully before signing it.
The team had finished the presentation the night before the client meeting.
Common mistake
The most common mistake: "I have seen him two days ago" is wrong because "ago" always goes with simple past, never with present perfect. Correct: "I saw him two days ago".
Trick to remember it
- •"Ago" measures time counting backward from now (always simple past).
- •"Before" shows something happened earlier than another past event: "She had left before I arrived".
Quick rule
- •"Ago" = from now backward, simple past only.
- •"Before" = before any reference point, often with past perfect.
Did you know?
"Ago" comes from the past participle of Old English "agan" (to pass, to go by). In earlier English the form was "two years agone", a variant that survived in 19th-century poetry ("O years agone!". Poe). "Agone" gradually disappeared from everyday speech, leaving behind "ago" as the modern standard form.
Practise what you learned
Exercise 1 · Pick the right one
She arrived three days _____ . She's been resting at the hotel since then.
Exercise 2 · Pick the right one
She had finished cooking _____ her husband got home.
Exercise 3 · Form the word
Related word pairs
'During' goes with named periods; 'for' goes with measured time durations.
"Since" marks the specific point when something started; "for" indicates how long something has lasted.
'Since' marks the starting point of something active until the present; 'ago' indicates distance into the past from now.
'Because' introduces the main cause or a new reason; 'since' and 'as' introduce secondary or already-known reasons.
Bryan López
Founder of SpeakUP Academy