1)Present perfect: to talk about an action completed in the past but it's effects are still in the present. #Eg. I have passed the test.(you could see the test results yesterday, but passing can be a present state) 2) past perfect:A tense which represents actions that occurred before other actions in the past. #eg. We had a good time before he got drunk and mess everything. 3) present perfect continuous: an action started in the present past and will continue #eg. I have been working hard on this paper.(I started working a while ago and will continue to work) 4) past perfect continuous: an action started in the past and continued up to a certain time in the past. #eg. We had been studying for an hour.( We studied from 00:00 to 00:60 minutes__ now we stopped studying)