I am confused by the tense in this sentence 「私は日本へ行く前に、中国のお土産を買った」


First, please look at this sentence:

> 私は日本へ行く前に、中国のお土産を買った。

Its English translation is:

> Before I will go to Japan, I bought some Chinese local goods.

which is very weird.

It is said that Japanese tense has relative tense which does not exist in
English.

Can you explain that for me?




> 私は日本へ行く前に、中国のお土産を買った。  
>  Before I will go to Japan, I bought some Chinese local goods.

The example sentence might be better translated this way:

  * "Before **going** to Japan, I bought some Chinese souvenirs." 

OP - "It is said that Japanese tense has relative tense which does not exist
in English."

Perhaps what is meant by "relative tense" is that the verbs in the two clauses
_do often need_ to agree in tense in English, but they _don't need_ to be in
the same form for Japanese, in fact that would be incorrect for this sentence.

However, the primary difference between 行く and 行った in Japanese is not a
difference of "tense"（時制）, it is a difference of "aspect"（相）. Aspect is
_affected_ by tense, but they are not always equivalent.

In other words,

  * **行く** describes an **_incomplete action_** (which may take place in the past, present, future or even habitually), but... 
  * **行った** describes a **_completed action_** (which may take place in the past, present or future)

If you look at the Japanese example sentence again with this viewpoint it
should make more sense.

> 私は日本へ **行く前に** 、中国の **お土産を買った** 。

  * **行く前に** - "before going" (not complete because 行く is describing a point "before" the action of "going" takes place) 
  * **お土産を買った** - "bought souvenirs" (complete because the speaker has already completed the action of buying)

These articles may be a good reference:

  * [http://www.ravco.jp/cat/view.php?cat_id=5173&PHPSESSID=803go89rdjn9hbqk4nn8qn3uc6](http://www.ravco.jp/cat/view.php?cat_id=5173&PHPSESSID=803go89rdjn9hbqk4nn8qn3uc6)

  * <http://repository.tufs.ac.jp/bitstream/10108/24091/1/acs073001.pdf>..  
(page 11, Section 3.2,「日本語の相」)

  * <http://www.tomojuku.com/blog/aspect/>

