As for the strange capabilities of Present Perfect, many grammar writers would not use one stone to kill the two birds:
Ex1: He has lived in Japan in the past five years. (a continuity)
Ex2: He has lived in Japan in the past. (a finish)
They would explain the tense separately in a few directions, as in:
Oh, of course, they will not tell you clearly, there are contrarieties in their items of Uses. :?
However, if you point out that Use#1 and Use#2 are not compatible, then they will admit, yes, they are aware of that. "The tense is very useful, isn't it?", they would join you.
However, I am afraid they themselves even don't know, Use#1 has unknowingly confused with use of Simple Present. Actually, Use#1 is the use of Simple Present:
Ex: Jack lives in Japan.
== Though in Simple Present, the living started in the past and are still continuing.
:idea: That is, Jack couldn't just live there only by the moment we speak or write. He must have started the living in the past, and are still continuing up to now.
Unknowingly or secretly, grammar writers borrow the definition of Simple Present to define Present Perfect, so that it looks like to have a difference from Simple Past. It has passed most people.
As for Use#2, again unknowingly or secretly, it is the use of Simple Past and can explain all Simple Past structures that don't carry a known time:
Ex: He lived in Japan.
Ex: She met him in the park.
In dealing with Present Perfect now, grammar writers are quite safe and self-contented, for usually students cannot see through the magic. Since writers have collected explanations and definitions prepared for both present and past time, what kind of Time situation Present Perfect cannot explain?
The tense can even stay with the Past Family, specific past time adverbials. As for the Past Family, including "since 1987", clearly telling the Time, they clarify the myth that Present Perfect is an Aspect which is not about Time/Tense. Actually, Present Perfect is a tense, which tells the time.
The exact reason why we have a hard time in explaining Present Perfect is that the tense seems able to express any Time. In fact, it does.
:idea: Present Perfect has a dual function, expressing either present or past. It then functions as either Simple Present or Simple Past. And this is why I have promised that, whatever you say to Present Perfect, can be said word for word again to either Simple Present or Simple Past.
Most people know we have a difficulty to tell Simple Past apart from Present Perfect. People admit this, in various forums or discussions.
But few people know there is another difficulty: to tell a difference between the use of Simple Present and Present Perfect. As the latter difficulty is known to few persons, in various forums, readers thought it was easy to prove me wrong. They just couldn't. Whatever they say to Simple Present can be word for word said again to another tense.
Ironically, when we bring the two difficulties together side by side, there is the answer emerging, a simple answer to the three tenses: Simple Past, Present Perfect, and Simple Present. In various forums readers eventually agreed, after looking at the simple answer, that it is nonsensical not to put the three tenses together for contrast.
Ex1: He has lived in Japan in the past five years. (a continuity)
Ex2: He has lived in Japan in the past. (a finish)
They would explain the tense separately in a few directions, as in:
My reply: Here Use#1 can explain my Ex1, and Use#2 my Ex2.Use 1: Actions which started in the past and are still continuing
Use 2: Actions which happened at some unknown time in the past
Use 3: Actions which happened in the past, but have an effect in the present
http://web2.uvcs.uvic.ca/elc/studyzone/330/grammar/upperf.htm
Oh, of course, they will not tell you clearly, there are contrarieties in their items of Uses. :?
However, if you point out that Use#1 and Use#2 are not compatible, then they will admit, yes, they are aware of that. "The tense is very useful, isn't it?", they would join you.
However, I am afraid they themselves even don't know, Use#1 has unknowingly confused with use of Simple Present. Actually, Use#1 is the use of Simple Present:
Ex: Jack lives in Japan.
== Though in Simple Present, the living started in the past and are still continuing.
:idea: That is, Jack couldn't just live there only by the moment we speak or write. He must have started the living in the past, and are still continuing up to now.
Unknowingly or secretly, grammar writers borrow the definition of Simple Present to define Present Perfect, so that it looks like to have a difference from Simple Past. It has passed most people.
As for Use#2, again unknowingly or secretly, it is the use of Simple Past and can explain all Simple Past structures that don't carry a known time:
Ex: He lived in Japan.
Ex: She met him in the park.
In dealing with Present Perfect now, grammar writers are quite safe and self-contented, for usually students cannot see through the magic. Since writers have collected explanations and definitions prepared for both present and past time, what kind of Time situation Present Perfect cannot explain?
The tense can even stay with the Past Family, specific past time adverbials. As for the Past Family, including "since 1987", clearly telling the Time, they clarify the myth that Present Perfect is an Aspect which is not about Time/Tense. Actually, Present Perfect is a tense, which tells the time.
The exact reason why we have a hard time in explaining Present Perfect is that the tense seems able to express any Time. In fact, it does.
:idea: Present Perfect has a dual function, expressing either present or past. It then functions as either Simple Present or Simple Past. And this is why I have promised that, whatever you say to Present Perfect, can be said word for word again to either Simple Present or Simple Past.
Most people know we have a difficulty to tell Simple Past apart from Present Perfect. People admit this, in various forums or discussions.
But few people know there is another difficulty: to tell a difference between the use of Simple Present and Present Perfect. As the latter difficulty is known to few persons, in various forums, readers thought it was easy to prove me wrong. They just couldn't. Whatever they say to Simple Present can be word for word said again to another tense.
Ironically, when we bring the two difficulties together side by side, there is the answer emerging, a simple answer to the three tenses: Simple Past, Present Perfect, and Simple Present. In various forums readers eventually agreed, after looking at the simple answer, that it is nonsensical not to put the three tenses together for contrast.