The Mandarin Chinese expression for “ought to” or “should” is yīng gāi. It consists of two characters: 應 (yīng) in this context means “ought to” and 該 (gāi) means “should” or “ought to.”

Yīng gāi is sometimes shortened to gāi.
Examples of Ying Gai
 
    Nǐ yīng gāi xué gāng qín.
    你應該學鋼琴.
    你应该学钢琴.
    You should learn how to play the piano.

    Wǒ gāi zǒu le.
    我該走了｡
    我该走了｡
    I should be going.