I was searching for something and I didn't find it. So I would say to my friend:
I searched for it but I didn't find it.
or
I've searched but haven't found it.
What is the difference between them?
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Sign up to join this communityTL/DR:
I haven't found it.
Implies you will keep looking, as in I haven't found it...yet.
I didn't find it.
Implies that you will not continue the search.
There are three aspects to consider, when it comes to the decision present perfect versus simple past.
I searched for something but I didn't find anything.
There are no signal words, the actions are completely finished and there is maybe a consequence to the present, i.e. you were not able to find your wallet, so you'll have to ask someone for money.
I have searched for something but I haven't found it.
There are no signal words, actions are finished, so perfect seems not the best choice.
Here is my proposal:
I searched for my keys in the morning, unfortunately I haven't found them yet.
In the first part of the sentence, you have signal word for the past tense (time) and in the second part for the present perfect (yet).
NOTE: I am neither a native speaker nor an expert - I am just trying to help!
To distinguish between past simple and present perfect simple tenses, you have to be aware about three important points here, which are :
For example: I phoned him 5 minutes ago. // I have just phoned him.
For example: I visited London last October. // I have been to London for some time (-> means that I went to London and I'm back now)
For example: I bought a car. (Just telling what I did it ) // I have bought a car ( I want to express what I did and expect your reflection on that).