1. If you had been born two hundred years ago,you would have had about one chance in eight of living to be one year old....
  2. In those days about seven out of eight babies died before reaching their first birthday.

I couldn't understand how to use ago and before in a sentence. Do they use alternately or any other way?


Ago measures a length of time into the past from now (the present).

At ten o'clock, an hour ago was nine o'clock. A year ago is (approximately) 365 days previously.

In quoted speech ago is used to refer to a length of time prior to the speech: In 2010 he said, "I gave up smoking three years ago."

Before marks a period prior to a particular point/day/year in history or an event/period.

Before means prior to/earlier than a time/date or an event.

Unlike ago, before does not usually relate to now

Before can refer to the past (*before he died) or to the future (before she arrives). It is always tied to a particular time or event.


In X ago, X must always be a period of time and the word will always follow the period of time.

I went two weeks ago.

In before X, X must refer to an event, or at least have a verb in it.

I went before the great flood happened.

I went before two weeks passed by.

  • Unless you say "Abraham lived before Noah". No verb there.
    – WS2
    May 5 '17 at 11:31
  • @WS2, that's an example of conversational elision. The real statement is "Abraham lived before Noah lived" or "Abraham lived before Noah did."
    – LawrenceC
    May 5 '17 at 12:08
  • So how about "Abraham lived before the time of Noah"? Or how about "Abraham Lincoln lived before 1900*?
    – WS2
    May 5 '17 at 12:53
  • I would argue that those are events - or points of time, not really meant per se as periods of time. "The time of Noah" and "before 1900" are expressions that are trying to relate the event to a (historical) point in time, the duration or period of time they also mean is secondary.
    – LawrenceC
    May 5 '17 at 13:05

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