Main Difference: Ago and Before are two words that have the same meaning, but these words cannot be used interchangeably. The main difference between Ago and Before exists in their usages. Ago is used to indicate some unknown time before the present while before is used after an expression of time that counts back from a past moment.
Ago – Meaning and Usage
Ago is an adverb meaning ‘before the present or earlier’. Ago is always used with a specific time period. The sentences that use ago are generally written in the simple past tense.
I went to Berlin six years ago.
He called you five minutes ago.
It happened a long time ago.
She went to school with me 15 years ago.
Before – Meaning and Usage
Before can be used as a preposition, conjunction and an adverb. It can be used after an expression of time that counts back from a past moment. Such sentences are generally in past perfect tense. For example,
When I called her last year, she said that they had shifted to Mumbai 6 years before.
By the time they arrived, I had already finished dinner.
Before can be also used without an expression of time to mean any time before now. Here a specific time is not given. For example, in the sentence, “I have seen her before.” Before refers to an unknown time period and does not define when. Similarly,
I have never been there before.
She said that she had never seen this man before.
In addition to this meaning related to time, before could also mean, ‘in front of’ and ‘in preference to’.
She stood before the mirror and admired her dress. (Before=in front of)
I would die before revealing that secret. (Before=rather than)
Difference Between Ago and Before
Ago is an adverb.
Before is an adverb, preposition and conjunction.
Ago is generally used with Simple Past.
Before is often used with past perfect tense.
Specific Time Period
Ago is used with a specific time period.
Before is not used with a specific time period.
Ago always counts back from the present time.
Before counts back from a past point.