We have been discussing this matter with a friend of mine who is an English teacher. On some examples, we both have been confused. Some of those examples are the followings;
Atatürk (died1938) has founded the Turkish Republic .
Present perfect tense(ppt) is used because The republic's been continuing to exist.
Atatürk founded the Turkish Republic .
Past simple(ps) is used because the action of founding completed (in 1923)
2) He has come (he is here)
He came (He is not here)
He came (He's here, ps is used here because the act of coming is completed and what's continuing for him is "to be here"-an other verb)
3)This one is my friend's explanation for a third example.
I lost my wallet (I know that my wallet is lost-I still don't have it)
I've lost my wallet (I have just noticed that my wallet is lost-I still don't have it)
I usually good at using ppt when it comes to experiences, specified time and continuing periods. It is also easy in tests when the tips such as yet, since, for, etc. are given. What confuses my mind about ppt is mainly focused on the continuing effect of a verb that completed in the past as it is given in the examples. I'll be grateful if you help me clarifying my mind.
Thanks for your replies in advance.