What are the different meanings of ''promise'' in past simple and present perfect? I think they are not different when translating to my language, but it must be different right? There are two examples 1. The college principal promised to look into the matter. 2.The government has promised a full investigation into the disaster.
There is not a lot of difference between the two tenses here, and they can be used pretty much interchangeably.
There is a slightly different feel between the two, but it is not a strong difference. Because the simple past is a past tense, it makes things sound a bit more final, while using the present perfect has a feeling that things are still somewhat unfinished or in progress. So:
The college principal promised to look into the matter.
This has the feel of "... and that was the end of the matter."
On the other hand:
The government has promised a full investigation into the disaster.
Has a feeling of "... but we're still waiting for the results of the investigation" (or possibly "... but that may not actually happen"). There is still some aspect of the promise that seems to be up in the air, a bit.
But as I said, this is not a strong distinction, and you may come across cases where people use one or the other without necessarily intending that specific interpretation.
It should also be noted that there's nothing special about the verb "promise" in this regard. The same is generally true for many/most verbs when using past vs present perfect.