Before as an adverb
Before, as an adverb, means already, in the past and similar ideas.
- I have seen that film before.
Before can also mean at any time before the past moment that we are talking about. In this case a past perfect tense is used.
- She realized that she had seen him before.
We also use before after a time expression to count back from a past moment. A past perfect tense is normally used. Note that to count back from the present, we use ago, not before.
Before as a conjunction
The conjunction before is used to join one clause to another. Before and its clause can come either before or after the other clause.
- I will die before I surrender.
- Before I surrender, I will die. (Note the comma in the second structure.)
Tenses in before clauses
In a clause with before, we use a present tense to refer to the future.
- I will telephone you before I come. (NOT — before I will come.)
To emphasise the idea of completion, we often use present and past perfect tenses in before-clauses.
- You can’t go to bed before you have finished your homework.
In a formal style, we often use the structure before -ing.
- Please put out all lights before leaving the office.
Before as a preposition
The preposition before is normally used to refer to time.
- I must get home before nine o’clock.
Note that before can refer to place in a few cases:
a) to talk about the order in which people or things come in queues, lists etc.
- Your name comes before mine on the list.
b) to mean in the presence of
- He was brought before the judge.