Definition

1. Interrogative adverb:

   • Why: Used to ask for the reason, cause, or purpose behind an action, situation, or event.
   • For what reason: Used to inquire about the motivation or explanation for something.

2. Conjunction (in indirect questions):

   • Why / The reason why: Used to introduce a clause that explains a cause or reason, often following verbs like "know," "understand," or "wonder."

Usage Examples

• Interrogative adverb:

  • Tại sao bạn đến muộn? (Why are you late?)
  • Cô ấy hỏi tại sao trời mưa. (She asked why it is raining.)

• Conjunction:

  • Tôi không hiểu tại sao anh ấy buồn. (I don't understand why he is sad.)
  • Đó là lý do tại sao cô ấy rời đi. (That is the reason why she left.)

Advanced Usage

• "Tại sao không?": Why not? (Used to make a suggestion or express agreement).

  • Chúng ta đi xem phim nhé? – Tại sao không? (Shall we go see a movie? – Why not?)

• "Tại sao lại...?": Why on earth...? (Adds emphasis, often expressing surprise or frustration).

  • Tại sao lại có chuyện này? (Why on earth did this happen?)

Variants and Related Words

• Vì sao (interrogative phrase): Why, for what reason. (A more literary or formal synonym).

  • Vì sao bạn nghĩ vậy? (Why do you think so?)

• Sao (interrogative word): Why, how come. (A common, colloquial shortening of "tại sao").

  • Sao hôm nay yên tĩnh thế? (Why is it so quiet today?)

Synonyms

• Why: For what cause or reason.
• How come: Informal for asking the reason.
• For what reason: More formal phrasing.

Related Idioms and Phrases

• Biết tại sao: To know the reason why.

  • Tôi muốn biết tại sao. (I want to know why.)

• Tại sao chứ?: Why, though? (Used to challenge or seek further clarification on a reason just given).

  • Anh không thích? Tại sao chứ? (You don't like it? Why, though?)

adv, noun

1. why, the reason why
   • tại sao lại như thế?
     why is that?