BEFORE AFTER

The time expressions after, before and when are used to indicate when something happens in the past, present or future. Each is a subordinating conjunction which introduces a dependent clause and can be used at the beginning or in the middle of a sentence.

• I went to school after I had finished my homework.
• She takes the train when she travels to London.
• Mary finished the report before she made the presentation.

or

• After we have discussed the issue, we can make a decision.
• When we get up, we take a shower.
• Before we left, we visited our friends in Seattle.

After, before and when introduce a full clause and require a subject and verb. Therefore, the time expressions after, before and when introduce adverb clauses.

After

The action in the main clause occurs after what occurs in the time clause with after. Notice the use of tenses:

Future: What will happen after something occurs.

Time clause: present simple
Main clause: future

• We'll discuss the plans after he gives the presentation.
• Jack is going to propose to Jane after they have dinner on Friday!

Present: What always happens after something else occurs.

Time clause: present simple
Main clause: present simple

• Alison checks her mail after she gets home.
• David plays golf after he mows the lawn on Saturdays.

Past: What happened after something (had) occurred.

Time clause: past simple or past perfect
Main clause: past simple

• They ordered 100 units after Tom (had) approved the estimate.
• Mary purchased a new car after she (had) researched all her options.

Before

The action in the main clause happens before the action described in the time clause with 'before'. Notice the use of tenses:

Future: What will happen before something else occurs in the future.

Time clause: present simple
Main clause: future

• Before he completes the report, he will check all the facts.
• Jennifer will speak with Jack before she makes a decision.

Present: What happens before something else occurs on a regular basis.

Time clause: present simple
Main clause: present simple

• I take a shower before I go to work.
• Doug exercises every evening before he eats dinner.

Past: What (had) happened before something else occurred at a point of time in the past.

Time clause: past simple
Main clause: past simple or past perfect

• She had already eaten before he arrived for the meeting.
• They finished the discussion before he changed his mind.