之所以

zhīsuǒyǐ
  1. (after a noun N and before a predicate P) the reason why N P
  2. Example: 我之所以讨厌他 wǒzhīsuǒyǐtǎoyàntā "the reason why I dislike him (is ...)"

CEDICT

Entry Composition

1 之 zhī
  1. (possessive particle, literary equivalent of 的 de)
  2. him
  3. her
  4. it
2 所以 suǒyǐ
  1. therefore
  2. as a result
  3. so
  4. the reason why