tức là

The conjunction tức là is an incredibly common and versatile tool in Vietnamese, used to mean 'that is,' 'namely,' or 'in other words.' It serves three main functions:

• Clarification and Restatement: It links two equivalent concepts, clarifying the first one. (e.g., 'Tôi sẽ gặp bạn vào thứ Hai, tức là ngày mai.' - I will meet you on Monday, that is, tomorrow.) This is also commonly used to expand acronyms in formal speech or news (e.g., 'WHO, tức là Tổ chức Y tế Thế giới' - WHO, namely the World Health Organization).
• Logical Deduction: It introduces a conclusion based on a previous statement or situation. (e.g., 'Anh ấy không trả lời, tức là anh ấy không đồng ý.' - He didn't answer, which means he doesn't agree.)
• Logical Equivalence: It is used to express logical equivalence or deductions between steps in mathematics or logic (e.g., 'x là số chẵn, tức là x = 2k'). Note that it is not used to read an equals sign in a simple equation, which uses bằng.

In everyday conversation, you will frequently hear native speakers start a sentence with Tức là...? to check their understanding or prompt someone to get to the point, similar to saying 'So what you're saying is...?' or 'So you mean...?' in English. A highly common set phrase is Tức là sao? (What do you mean? / How so?), which is often used as a standalone question. Additionally, tức là is frequently used as a conversational filler in spoken Vietnamese (similar to 'I mean...' or 'Like...' in English) when a speaker pauses to gather their thoughts. It is also frequently paired with conditional statements, such as Nếu... tức là... (If... that means...), and appears in common collocations like Nói tóm lại, tức là... (In short, that is...) or Nói cách khác, tức là... (In other words, that is...).

Crucial Distinction: Learners often confuse tức là with nghĩa là (or its very common variant có nghĩa là, which literally means 'has the meaning of'). While they are sometimes interchangeable, native speakers strongly prefer nghĩa là for strict semantic definitions (like translating a vocabulary word) and tức là for logical deductions or identifying referents. For extra emphasis, speakers sometimes combine the two into the spoken form tức có nghĩa là... (which means...). Furthermore, while the native Vietnamese word tức functions as an adjective meaning 'angry,' the tức in tức là comes from a Sino-Vietnamese root (即) meaning 'namely,' 'exactly,' or 'promptly.' Combined with là (to be), it literally translates to 'namely is' or 'exactly is.' In formal or literary contexts, this tức is sometimes used alone as a short-form conjunction.