How to say "Why I started studying Japanese"


I have a Japanese assignment that requires me to write about anything I want.
I decided that I wanted to write about why I want to learn Japanese. I think
the title should be "Why I want to study Japanese"; would 私は日本語を勉強したい理由 work?
I am not sure if I am using 理由 correctly here.




> 「私 **は** 日本語を勉強したい理由」

This is a nice try, but the 「は」 needs to be replaced by a 「が」. 「は」 is not an
option here. Why not?

That is because 「私 **が** 日本語を勉強したい」 is a relative clause that modifies 「理由」,
correct?

**Inside if-clauses and relative clauses, the subject/topic marker is always
「が」**.

We say:

「ジョーンズさん **が** 買った車はBMWです。」

「あなた **が** 日本に行くなら、私もいっしょに行きたい。」

The 「が」 in either sentence cannot be replaced by a 「は」. I might even add that
this particular mistake in the particle choice sounds more serious to us
native speakers than you might think.

Finally, you are using 「理由」 correctly.

