Definition

1. Adverbial phrase:
   • Ought to, should have: Used to express that something was expected, proper, or logical to happen in the past but did not. It conveys a sense of missed opportunity, regret, or correction of an assumption.
   • Normally, by rights: Indicates what would be the normal, standard, or correct course of action or situation.

Usage Examples

• Expressing a missed expectation or regret: Đáng lẽ tôi nên học bài tối qua. (I ought to have studied last night.) Đáng lẽ cô ấy đã thắng cuộc thi. (She should have won the competition.)

• Correcting an assumption or stating the norm: Đáng lẽ anh phải là người đầu tiên đến. (Normally, you should be the first one to arrive.) Đáng lẽ trời phải mưa vào mùa này. (It should be raining this season by rights.)

Advanced Usage

• "Đáng lẽ ra": This is a more emphatic or formal variant with the same core meaning. Đáng lẽ ra chúng ta không nên đi con đường này. (We really ought not to have taken this road.)

• Used to introduce a hypothetical or contrary-to-fact past condition, often paired with a consequence clause using "đã" (would have). Đáng lẽ tôi đi sớm, tôi đã không bị lỡ tàu. (If I had left early, I wouldn't have missed the train. / I ought to have left early; then I wouldn't have missed the train.)

Variants and Related Words

• Lẽ ra: A slightly more conversational synonym for "đáng lẽ". (You should have known that.)
• Đáng nhẽ: A less common regional variant with the same meaning.
• Phải chi / Giá mà: Synonyms expressing wish or regret for an unrealized past condition ("If only..."). While similar in sentiment, they are conjunctions introducing a wish, whereas "đáng lẽ" is an adverbial phrase stating an obligation or norm. (If only I had more time.)

Synonyms

• Nên: should, ought to. ("Nên" is more direct for present/future advice; "đáng lẽ" implies the advised action is already in the past.)
• Phải: must, have to. ("Phải" indicates necessity or strong obligation.)

Related Phrases

• Đáng lẽ... thì đã...: A common correlative structure for contrasting what should have been with what actually happened or would have happened. (I ought to have bought a used car; then I would have saved money.)

Related Idioms

• Biết thế... đáng lẽ...: An expression of regret meaning "Had I known... I would have..." (Had I known, I ought to have stayed home.)

1. Ought to, normally