I just wonder if there's any rule or good role of thumb when the tone of the 2nd character changes to neutral.
I thought maybe repetition like 熱鬧 rènao, 糊涂 hútu, or 姐姐 jiějie but then there's 浪漫 làngmàn, 處理 chǔlǐ or 僅僅 jǐnjǐn.
Then, why does 維護 wéihù keep the 4th tone while 聰明 cōngming, 凉快 liángkuai, 清楚 qīngchu, and 糧食 liángshi change to 5th?
And qù and lái are most confusing:
Thanks for any ideas,