この哲学書は難解で、なかなか読み進められない。
This philosophy book is so difficult to understand that I can hardly get through it.
教授は難解な理論をわかりやすく説明してくれた。
The professor explained the abstruse theory in a way that was easy to follow.
彼の詩は難解だが、熱心な読者が多い。
His poetry is obscure, but it has many devoted readers.
契約書は難解な法律用語で書かれていた。
The contract was written in hard-to-understand legal terminology.