Can any one tell me how to teach the difference between past simple and present perfect?
Say for example:
"I went" and "I have gone"
Thanks in advance
The past simple tense is used for actions and events that are contained entirely within the past, with no connection to the present. The present perfect tense is used for actions and events that occurred in the past but are still strongly linked in some way to the present. This link can be temporal (events and actions continuing up to the present or ending only very recently) or otherwise (past influences that have present consequences).
The current tendency, especially in American English, is to greatly narrow the scope of the perfect tenses. Past events are usually referred to with the past simple unless their link to the present (temporal or otherwise) is very strong. The British will often say "have you eaten breakfast today?" but Americans will often say "did you eat breakfast today?" The difference is not one of grammar but of mental perspective on the events in question; Americans consider breakfast to already be in a detached past, whereas the British have a larger scope for recent events.
"The present perfect tense is used for actions and events that occurred in the past but are still strongly linked in some way to the present."
Except when talking about a one-time event action that cannot be repeated -- cf. the "Did you watch the program?" vs. "Have you done your homework" discussion. (In both cases, the speaker is interested in present consequences.)
Thank you Tom and Maxmanic
Cannot be repeated ... or wouldn't normally be repeated. You might have taped the programme or it might even be broadcast over and over again (like on BBC World). You might have done your homework but got it wrong (with misquotes or miscalculations) or the teacher might have thought it was too messy or insufficient. But besides finicky details like these I haven't got much more to add.
"Did you watch the program?" implies a specific time in the past, even though it isn't stated; such a specification normally requires a past simple tense. It implies "Did you watch the program [last night]?"