About SINCE

If John says "Ms JH has lived in Japan since 1987", shall I ask where Ms JH is living now? Or shall I suppose that Ms JH still lives in Japan, so I don't need to ask?

The sentence you quoted implies that JH still lives in Japan, because the verb was "has lived". If the verb were "had lived" that would say that JH
no longer lives in Japan:

They had been friends since birth (until he died).
They have been friends since birth (and still are).

Thank you D.

But how about the following one in dialogue? It seems Since and Present Perfect imply a finish or completion.

A: John's just been fired!
B: What! What a shame, he's worked here since 198

B is just speaking as though John still works there. Since and present prefect imply continuining action, never completion.

*continuing

The A/B sentences that TB posted are fine. Native speakers
don't follow all the rules all the time, and the A/B exchange is
one situation where the need for 'had' to be in the past
is more important than the rule that 'has' is not used for
completed actions. That is, B could not use the word
'had' because the firing was not, in his view, in the past.
The firing was in the present, because A said John
had _just_ been fired.

Consider:

A': John was fired two weeks ago.
B': What a shame. He worked here for 25 years.

Here, B' uses 'had' because the firing was in the past.
B' could not use the word 'has'.

From D:
> the rule that 'has' is not used for completed actions.
>

What does this mean? I don't understand at all.

Ex: He HAS been there.
Ex: He HAS worked in that factory.
Ex: She knows Japanese because she HAS lived in Japan.

HAS is used for completed action.

TS: The way I see it, the sentences in your last post
don't represent "completed actions," they describe how
something was at a particular moment in time. For whatever
reason, so long as the decription remains valid English uses
'has' and doesn't consider the action to be completed --
after all, if I have been in Japan I might go back.

The sentence

(1) He had arrived at the store two times.

is different than

(2) He has arrived at the store two times.

because the verb had in (1) tells me that I should view the
sentence (1) as being completed in the past. I don't
expect him to arrive again; instead, I expect something else
to happen.

In sentence (2) the verb has tells me I should imagine that
he is still going, and he might arrive again.

For example, I have seen two movies this month.
I might see more movies -- the action "seeing movies this month"
is not completed until the month is over.

Next month, I can't say "I have seen two movies last month"
because the action "seeing movies last month" is completed.
I can never see another movie last month. This is the rule I
alluded to in a previous post by saying " 'has' is not used
for completed actions."

If you don't see what I mean by "completed action" then it
might be better to forget about that description of the difference
between had and has, and find some other way to see how they
are used.

I am afraid I cannot wholly agree to you. The HAS examples I gave are completed actions. Or else, we don't have completed actions at all.

> (2) He has arrived at the store two times.
>
I think it means only that the action has completed two times. The explanation is normal and acceptable.

> (1) He had arrived at the store two times.
>
> I don't expect him to arrive again; instead,
> I expect something else to happen.
>
The expectation is not possible because it can be never realized, unless you know he has passed away. Even he has moved to another country, he will still return and visit the store. How can you expect one will not go to a store again, if he has been there for a few times? Completion cannot be judged by such standard.

>How can you expect one will not go to a store again, if he has been there >for a few times? Completion cannot be judged by such standard

And yet it is. English speakers will consistently say "I have been to the
store three times" as long as there is a possibility they might
return, and "I went to the store three times" if there is no possibilty they
will return. Moreover, they will expect other speakers to follow this rule --
they will interpret what they hear in light of this rule.

If you don't want to agree with me, that's fine. I am only
trying to describe the reasoning that native speakers use to
decide whether they can use has/have.

Thank you D. You and 'Someone' seem to make it quite clear that Present Perfect, especially with Since, denotes an unfinish. But after a man passed away, for another example, in many epitaphs they still use "He has lived here since 1976" to state the last place he lived. And the epitaphs could last for some few years. If so, the use of Since is not exactly as you describe it. It is also used for something completed.

Is there an explanation?

"He has lived here since 1976." could not be said about a dead person. It would have to be "had".

No, it is very frequent that we use HAS LIVED in obituraries:

Marcella L. Harris (nee Dial) ?83 of Avon Lake, formerly of Cleveland, passed away, Sunday, March 14 at Community Health Partners Hospital and Surgical Center, from complications of pneumonia. Mrs. Harris was born May 9, 1920 in Cleveland and HAS LIVED in Avon Lake since 1958.
http://www.buschfuneral.com/obits/obituary.html?obituaryid=2327
-----------
Mr. Durham was a native of Kentucky and came to Oklahoma at the time of the opening in 1889 and HAS LIVED in Payne county since then. 
http://myweb.cableone.net/4jdurham/durham/durhamaj.html
-----------
She later moved to Corinth, MS, and HAS LIVED in Memphis, TN since 1987.
http://home.att.net/~SGTAYLOR1/gascoigne/dwghartfordcur.html
-----------
He married Myrtle M. Perry on June 26, 1929 and she passed away on September 16, 2001. He HAS LIVED in Newton Falls since 1997 formerly of Huddy, Ky.
http://www.williamsondailynews.com/041016.html

I can claim as many examples as you want.

I don't think that obituaries are the best place to learn English --
they are often written by family members or by the staff of
the funeral home. It isn't surprising that people, in a time of
grief, use language that implies that the dead person isn't
really dead.

Some of the obituaries above seem to use "has lived"
to mean that the person lived in that place until death -- this
could be just to save space in the newspaper, where you
sometimes must pay by the word to publish an obituary.
In non-newspaper contexts, English does not allow you to
use the wrong tense to save space. In newspapers, space
is at a premium, so there are many "mistakes" like these which
are really only space-saving devices. Educated speakers know
not to write like the papers.