History of Chinese Scoring
It is believed that the original scoring method in China (perhaps around 500 B.C. ?) simply counts the number of stones remained on the board. Therefore people would not pass but keep playing until no more living stones could be added on the board. Generally (except seki etc.), all of one's own territory would be filled up except for the two eyes required to keep each group alive.
The scoring system changed later for the sake of convenenice. According to "Dun Huang Qi Jing" (dated around A.D. 500, one of the oldest Go documents found), the rule of scoring at that time was: First, both players should have played the same number of stones. Next, remove dead stones. Then (make a new word, "Land") was defined as,
"a place where you can put in a living stone".
Your score was your Land minus your dead stones (which looks like Japanese rules, and indeed Go was introduced to Japan at around A.D. 800). But the important difference is that the two basic eye-spaces for each group did not score (without two eyes the group is dead !). This was implemented by imposing a two point group tax on the territory of each independent living group. In other words, the two points that are the eyes required for life don't count for the score. The resulting score was expected to be equivalent to the original case.
During Ming Dynasty (around A.D. 1400), the scoring method changed again to count Land plus living stones (the "unfilled stone counting"). Reason for the change is unknown (from the documents). The group tax was still implementing in order to keep the resulting score equivalent to the original case.
At around 1950s Chinese replaced "Land" by "Territory" (which is the set of empty intersections enclosed by stones of same color). The final score is then different from before. The modern Chinese rule emerged in this way.
See Ancient Chinese Rules And Philosophy for more context.
Bill: There is also speculation that the earliest form of go was scored by counting prisoners. Curiously, prisoner scoring with no passes and stone scoring are almost equivalent, as is territory scoring with a group tax.
reason:Reason for the change is:under original rules,it is easy to do,if someone steal another's stones,a trick,he will win.So,changed.