两 + Measure word vs 二 (naming/counting the number)
二 (èr) vs 两 (liǎng) — counting a number vs quantifying things
两 (liǎng) and 二 (èr) both mean 'two', but they aren't interchangeable. Use 两 right before a measure word when you're counting a quantity of things: 两个人 (two people), 两本书 (two books), 两天 (two days). Use 二 when you're naming or reciting the number itself — sequential counting (一, 二, 三...), phone numbers, page numbers, floor numbers, math, and inside compound numbers like 二十 (20) or 二百 (200). The deciding question: am I counting 'how many things' (→两 + measure word), or just stating/reading the number or label 'two' (→二)? One exception worth memorizing: even though floor/room numbers look like quantities, they're really labels, so they take 二 (二楼, not 两楼).
Examples
- 我有两个妹妹。wǒ yǒu liǎng ge mèi mei
I have two younger sisters.
- 他住在二楼。tā zhù zài èr lóu
He lives on the second floor.
- 我买了两本书，一本二十块，一本二十二块。wǒ mǎi le liǎng běn shū, yì běn èr shí kuài, yì běn èr shí èr kuài
I bought two books, one for 20 yuan, one for 22 yuan.
Common mistake
✗ Wrong: 我住在两楼。
✓ Right: 我住在二楼。
Floor numbers name the ordinal number itself (like a label), so use 二, not 两 — 二楼 (2nd floor), not 两楼. 两 only appears directly before a measure word counting a quantity of things.
Practice this pattern
Fill in the missing character:
我有＿个妹妹。
I have two younger sisters.