còn ... thì ...

The pattern còn ... thì ... is an essential tool for comparing and contrasting in Vietnamese.

Structure:
[Context/Clause 1], còn + [New Topic] + (thì) + [Comment].

Key Nuances:

• Topic Shifting: It acts as a conjunction meaning 'as for' or 'whereas', signaling a shift in attention to a new topic. Do not confuse it with the adverb còn meaning 'still', or the verb meaning 'to remain' or 'to have left' (e.g., 'Tôi chỉ còn 50 ngàn').
• Types of Topics: The new topic introduced by còn does not have to be a person or pronoun. It can also be a time phrase, a place, or an object (e.g., 'Hôm nay tôi rảnh, còn ngày mai thì bận' - Today I am free, whereas tomorrow I am busy).
• The Role of 'thì': Learners often first encounter thì meaning 'then' in the nếu ... thì ... pattern. Here, however, it functions purely as a topic marker to highlight the new subject. Crucially, thì is completely optional. The word còn alone works perfectly fine to mean 'whereas' (e.g., 'Tôi thích trà, còn anh ấy thích cà phê'). In everyday speech, thì is heavily used as a natural filler, but it is often omitted in concise formal writing.
• Cross-Sentence Usage: While often used to connect clauses in a single sentence, còn frequently starts a brand-new sentence, especially in dialogue to reply to someone else's statement. For example, Person A: 'Tôi uống trà.' / Person B: 'Còn tôi thì uống cà phê.'
• Versus 'Nhưng' (But): While nhưng expresses a direct contradiction or unexpected result, còn is used for neutral contrast or parallel comparison between different subjects (e.g., 'I like tea, whereas he likes coffee'). Crucially, when used to mean 'whereas', còn generally requires different subjects/topics. You cannot use it to contrast two traits of the same subject in this way (e.g., 'He is rich, còn he is unhappy' is incorrect; you must use nhưng), unless the sub-topic shifts (e.g., 'Anh ấy rất giỏi Toán, còn Tiếng Anh thì dở' - He is very good at Math, whereas his English is bad).
• Bouncing Questions Back: A highly common conversational application is the set phrase Còn [Topic] thì sao? (And how about [Topic]?). This is used to bounce a question back to someone or ask for their situation. For example: 'Tôi khỏe. Còn bạn thì sao?' (I am well. And how about you?). In casual speech, it is incredibly common to drop 'thì sao' entirely and just ask 'Còn [Topic]?' (e.g., 'Tôi khỏe. Còn bạn?').
• Chaining in a List: Còn is frequently used to introduce the final item in a list of contrasting subjects, functioning similarly to 'and/whereas' at the end of a list (e.g., 'Lan uống trà, Nam uống nước trái cây, còn tôi thì uống cà phê.').
• Not 'Là' (To be): Because thì often appears before adjectives where English uses 'is/are', learners sometimes confuse it with a verb. Remember that thì connects the topic to its comment, unlike the verb là. Crucially, thì does not replace là when the comment is a noun; they can be used together (e.g., 'Tôi là sinh viên, còn anh ấy thì là giáo viên.').

This pattern is extremely frequent and perfectly natural in both highly formal contexts and casual everyday speech.