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• In general, the past simple is used to refer to periods of time or moments which are finished. The present perfect is used to refer to periods of time which continue up to the present.
✓ The nineteenth century saw many technological advances, such as the camera and the electric light bulb.
✓ There have been many technological advances in recent years, the most important being the spread of the Internet.
• The past simple is used to refer to events at a specific time in the past. The present perfect is used when the specific time something happened isn't important or relevant, or when the present result of a past event is important.
✓ I sent my first e-mail six months ago.
✓ Have you ever sent an e-mail before?
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