I wanted to say: there is a pen. Hence, I said

> ペンはある

But my girlfriend said to me that one has to say:

> ペンがある。

But she can't explain to me why, and I don't understand.

Do you have an explanation?  
Thanks in advance!
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2016-05-21T21:56:46.577
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2020-12-30T11:18:32.830
2020-12-30T11:18:32.830
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question
particles subjects
Why can't I use は with ある?
I feel that the distinctions between は and が are one of the hardest parts to
learn about the Japanese language, so I'll try to keep things mostly focused
on this example.

> ペンはある

Here "は” marks ”ペン" as a "topic", rather a "subject", but what that really
translates into is a feeling of:

> There _is_ a pen (but there isn't a ....)

This is because that "は" also is commonly used to indicate that what follows
it applies to the thing before the は, but _not_ to something else which may or
may not be directly stated.

Here is an example where the thing that doesn't apply is directly stated:

> ペンはあるけど、鉛筆はない

In fact は tends to be used more frequently with negative verbs (hence the は
part of ではない). So if you are saying "the pen isn't there", this would be
completely natural:

> ペンはない

However, if there was a situation where someone was panicking and somebody
asked them "What is wrong?" (どうしたの？), they could very well reply using が
instead:

> ペンがないよ！

This is because が strongly emphasizes the subject, and is generally used when
there was some uncertainty about a subject which is being clarified.
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2016-05-22T03:00:16.277
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2016-05-22T03:00:16.277
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answer
That would be 「ペン **が** ある。」 100% of the time.

「ペン **が** ある。」 (= "There is a pen.") is a statement about 'what is there' or
'what the speaker has just found at a particular location". It is **_not_** a
statement that gives some kind of description about either pens in general or
a particular pen.

If you desire to make a further statement about the pen **_after_** you have
found it and said 「ペン **が** ある。」, you can use 「 **は** 」 as in 「そのペン **は**
とても[長]{なが}い。」= "The pen is very long." and such .

「ペン **は** ある。」, as a stand-alone statement, sounds **_far more weird_** to us
Japanese-speakers than you could probably imagine at this stage. You could
look like you were trying a make a profound philosophical statement about pens
in general. I call that the power of particles - "POP" for short. Learning
Japanese means learning POP.

If you go outside of your house and find a dog right in front of you, you will
say 「イヌ **が** いる。」. If you said 「イヌ **は** いる。」 instead, people would wonder if
you were OK because you would look as if you were making a metaphysical
statement about dogs and the universe outside of your front door on your way
to Burger King.
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2016-05-25T06:21:05.373
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2016-05-25T06:21:05.373
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answer