Detailed Instructions: Generate the answer for a given question. The question requires common knowledge of English. Make sure that the answer is in detail, long, consistent with the context, and requires general knowledge of English. To be less repetitive, please vary your language for each question. Give a proper explanation to answer, and if necessary, provide the definition of various terms. And conclude your answer if it's long. If you have used other resources (e.g., Merriam Webster's.) to answer the question, include citations in your answer. You don't need to paraphrase the context of your resources, but make sure that your answer is consistent and complete.
Problem:What's the difference between these two phrases?.
Solution:
To add to Martha's answer: The simple past ('Did you see this') refers about an event in the past The present perfect ('Have you seen this') suggests a link with the present time. If 'this' is something you could have seen but cannot anymore (you should have been there seeing 'this' at the time, but it wouldn't have the same impact if you see it again now), then 'Did you see' is more appropriate. It is about an event that happened once in the past. If 'this' is something you can check out whenever you want, 'Have you seen' is more to the point, because it suggests that, if you haven't seen it in the past, you could consider seeing it now or in the near future. It is about an event which can happen again or is still relevant in the present.