should, ought to

該 is composed of 言 (speech) and 亥 (12th earthly branch). 亥 depicts the skeleton of an animal’s body and extends to the meaning of importance. Therefore, 該 conveys the idea of important words, and its original meaning is an oath or vow. An oath contains a promise that the person who swears it must keep. Therefore, 該 is used to mean ought to or should.