之所以

zhī suǒ yǐzhisuoyi

1. (after a noun N and before a predicate P) the reason why N P
2. Example: 我之所以討厭他|我之所以讨厌他[wo3 zhi1 suo3 yi3 tao3 yan4 ta1] "the reason why I dislike him (is ...)"

Study it in Yanamino