Present perfect or past simple? (have seen / saw)

Rules

• Rule 1: Finished time → past simple

  If the sentence has a finished time like yesterday, last week, in 2020, two days ago, when I was…, use the past simple.

  Pattern: subject + past form + finished time

  Example: We played chess yesterday.

  Example: She was born in 2015.

• Rule 2: No time / experience → present perfect

  For life experiences (ever, never) or when we don't say when, use the present perfect.

  Pattern: subject + have / has + past participle

  Example: Have you ever ridden a horse?

  Example: I have never tried snails.

• Rule 3: Result now → present perfect

  If the result of a past action matters now, use the present perfect: just, already, yet. (In everyday American English, the past simple is also common with these words: *I just ate. / Did you finish yet?*)

  Example: I have lost my pen. Can I borrow yours?

  Example: The bus has just left.

• Rule 4: Unfinished time → present perfect

  With time periods that aren't over yet, like today, this week, this year, so far, use the present perfect. (In everyday American English you may also hear the past simple with *today* or *this week*, but so far always takes the present perfect.)

  Example: I have drunk four glasses of water today.

  Example: We have learned a lot this year.

Common mistakes

• I have seen him yesterday. → I saw him yesterday.

  yesterday → past simple.

• When have you arrived? → When did you arrive?

  When questions → past simple.

• I have finished it two hours ago. → I finished it two hours ago.

  ago → past simple.