"Since" marks the STARTING POINT of something that remains active until the present; "ago" indicates a distance in time toward the PAST from the present.
SINCE: indicates the STARTING POINT of a situation or action that CONTINUES until the present (or until a reference moment). "I have worked here since 2019" = I started in 2019 and I am still here (the situation remains active). SINCE typically goes with PRESENT PERFECT or PAST PERFECT: "She has been here since Monday" / "He had been waiting since noon." SINCE can introduce a date ("since 2020"), an event ("since the merger"), or a clause ("since she arrived"). IMPORTANT: SINCE marks a POINT IN TIME, not a duration. For durations use FOR: "I have worked here FOR five years" (duration of 5 years) vs "since 2019" (starting point).
She has been the head of the department since the previous director retired two years ago — the transition was seamless.
The company has been listed on the stock exchange since 2018 and has grown its market capitalization by nearly 400 percent since then.
Since the new performance management system was introduced, employee satisfaction scores have improved consistently quarter over quarter.
AGO: time adverb indicating that something happened in the PAST, at a specific distance in time BEFORE THE PRESENT. "Two years ago" = two years before now. "I moved here three months ago" = I moved three months before the current moment. AGO always looks toward the PAST from the present and always expresses DISTANCE: how far back. AGO typically goes with the SIMPLE PAST: "She called an hour ago." NEVER with present perfect: "She has called an hour ago" = INCORRECT. Structure: AMOUNT OF TIME + AGO: "five minutes ago", "two weeks ago", "three years ago."
She joined the company three years ago and has since been promoted twice, most recently to regional director.
The technology that felt innovative just a decade ago now seems almost quaint compared to the current capabilities of AI systems.
We submitted the application six weeks ago and have not received any confirmation or acknowledgment from the licensing authority.
Common mistake
The two classic errors: (1) "I moved here since three years" = INCORRECT. SINCE marks a POINT IN TIME ("since 2021"), not a duration ("three years"). For duration use FOR: "I have lived here FOR three years." (2) "She called me since an hour ago" = INCORRECT. SINCE and AGO do not combine. "She called me AN HOUR AGO" (simple past + ago). Or: "She has been calling since noon" (present perfect + since + point). (3) "She has arrived two hours ago" = INCORRECT. AGO goes with SIMPLE PAST, never with present perfect: "She ARRIVED two hours ago." (4) "I know him since five years" = DOUBLE ERROR: neither "know" nor "five years" work with since. Correct: "I have known him FOR five years" / "since 2019."
Trick to remember it
THE RULE OF THREE: AGO goes with SIMPLE PAST. SINCE goes with PRESENT PERFECT (or PAST PERFECT). FOR goes with PRESENT PERFECT (or PAST PERFECT) for durations. Diagnostic question: are you talking about WHEN something happened (point in the past)? = AGO + simple past. Are you talking about the STARTING POINT of something still active? = SINCE + present perfect. Are you talking about HOW LONG something has lasted? = FOR + present perfect. "She left THREE HOURS AGO" (when she left, past point). "She has been away SINCE this morning" (when she started being away, still active). "She has been away FOR three hours" (how long she has been away, duration).
Quick rule
Since = starting POINT until now (+ present perfect). Ago = distance to PAST from now (+ simple past). For = total DURATION (+ present perfect). "Since 2020" (when it started). "Two years ago" (when it happened). "For two years" (how long).
Did you know?
The word "ago" is one of the oldest terms in English still in active use. It comes from the Old English "agan" meaning "to pass" (as in passing time). In Early Modern English (14th-16th centuries), "ago" was still used in expressions like "long ago past" (a long time ago). Interestingly, in Shakespeare's English, "ago" was frequently replaced by "since" or "past" with the same meaning, and the modern distinction between the three words was much less systematic. The grammaticalization of AGO as an exclusive adverb of DISTANCE TO THE PAST (always with simple past) is a regularization that occurred gradually between the 17th and 19th centuries and is today one of the most uniform rules in modern English.
Exercise 1 · Pick the right one
The company has been operating in the Latin American market _____ it acquired a regional distributor in 2017.
Exercise 2 · Pick the right one
I submitted my application for the grant more than three months _____ and have not received any response from the committee.
Exercise 3 · Form the word
Since = starting POINT until now (+ present perfect). Ago = distance to PAST from now (+ simple past). For = total DURATION (+ present perfect). "Since 2020" (when it started). "Two years ago" (when it happened). "For two years" (how long).
The two classic errors: (1) "I moved here since three years" = INCORRECT. SINCE marks a POINT IN TIME ("since 2021"), not a duration ("three years"). For duration use FOR: "I have lived here FOR three years." (2) "She called me since an hour ago" = INCORRECT. SINCE and AGO do not combine. "She called me AN HOUR AGO" (simple past + ago). Or: "She has been calling since noon" (present perfect + since + point). (3) "She has arrived two hours ago" = INCORRECT. AGO goes with SIMPLE PAST, never with present perfect: "She ARRIVED two hours ago." (4) "I know him since five years" = DOUBLE ERROR: neither "know" nor "five years" work with since. Correct: "I have known him FOR five years" / "since 2019."
THE RULE OF THREE: AGO goes with SIMPLE PAST. SINCE goes with PRESENT PERFECT (or PAST PERFECT). FOR goes with PRESENT PERFECT (or PAST PERFECT) for durations. Diagnostic question: are you talking about WHEN something happened (point in the past)? = AGO + simple past. Are you talking about the STARTING POINT of something still active? = SINCE + present perfect. Are you talking about HOW LONG something has lasted? = FOR + present perfect. "She left THREE HOURS AGO" (when she left, past point). "She has been away SINCE this morning" (when she started being away, still active). "She has been away FOR three hours" (how long she has been away, duration).
Bryan López
Founder of SpeakUP Academy