1. 二 is used as an ordinal number indicates the sequence.
第二(dì èr) the second，
二楼(èr lóu) the second floor.
2. “二” is used generally when counting in numbers, or performing mathematical functions, such as a fraction, or a decimal，“二” is used instead of “两”.
1、2、3、4…… 一、二、三、四…… (yī, èr, sān, sì)
1/2(èr fēn zhī yī) 二分之一;
2/3(sān fēn zhī èr) 三分之二
0.2(líng diǎn èr) 零点二；
2.4(èr diǎn sì) 二点四
1. When you want to say “two of” something, 两is used in front of measure words to express a quantity. This is similar in English to saying “a pair” of something, but it is used in Chinese to express having “two of” almost anything.
两个小时(liǎng gè xiǎo shí) two hours;
两天(liǎng tiān) two days;
两个星期(liǎng gè xīng qī) two weeks;
两个月(liǎng gè yuè) two months.
两双手(liǎng shuāngshǒu) two pairs of hands
两本书(liǎng běn shū) two books
There is one potentially confusing example about time.
Instead of saying 二点(èr diǎn) to express 2 o`clock, the correct way to express this is actually 两点(liǎng diǎn) 2 o’clock – you can think of it literally as a quantity of “two points on the clock.”
2. When you want to approximate a number, you can use “两”and either “一” or “三” together in succession.
一两天(yī liǎng tiān) One or two days.
这个词我们学了两三次了. (Zhè ge cí wǒ men xué le liǎng sān cì le.)
We’ve studied this word two or three times.
每个人要花两三百块钱。 (Měi gè rén yào huā liǎng sān bǎi kuài qián.) Everyone needs to spend two to three hundred RMB.
3. Only “两” can be used to refer to paired kinship, such as “兄弟(xiōngdì) brothers” “姐妹(jiěmèi) sisters” “兄妹(xiōngmèi) elder brother and younger sister” “姐弟(jiě dì) elder sister and younger brother” “夫妻(fūqī) husband and wife”.
NOTE that when talking about parents, we don’t say “两父母”.
他们两姐弟关系不好。(Tāmen liǎng jiě dì guānxì bù hǎo.) The relationship between the elder sister and younger brother is not good.
这两夫妻又吵架了。(Zhè liǎng fūqī yòu chǎojiàle.) This couple quarrelled again.
4. “两” is also often employed on its own to indicate a generally small quantity, whereas “二” cannot be used in this way.
怎么就来了这么两个人?(Zěn me jiù lái le zhè me liǎng gè rén?)
Why there are just so few people come?
In the multi-digit numbers, use 二，not 两 for tens place and ones place, as 22(二十二).
Before the百(hundred)’s place, either 两 or 二 can be used, as in 200(二百/两百).
When used before the “千”(qiān, thousand)、“万”(wàn, ten thousand) or “亿”(yì, hundred million) places, “两” is much more frequently used.
Before “traditional” units for capacity or weight (尺(chǐ)/亩(mǔ)/升(shēng)…), both 两 and 二 can usually be used.
二尺/两尺(èr chǐ /liǎng chǐ)；two feet
二亩/两亩(èr mǔ /liǎng mǔ)；two mu
二升/两升(èr shēng /liǎng shēng). Two liters
However, before the “new” units for capacity and weight, typically 两，is used.
两吨 (liǎng dūn) two ton
两公里 (liǎng gōnglǐ) two kilometers
Note that两 also means “1/20 of a kilogram”, so to make this distinction clear, two “1/20 kilo” is represented as 二两 (èr liǎng ), not 两两 (liǎng liǎng).
“俩(liǎ)” means “两个”, and is more commonly used as a colloquial term in northern China.
我们俩(我们两个, the two of us),
俩苹果(两个苹果, two apples).
贰 (also pronounced èr) is used to represent the number 2 on items like cheques to prevent forgery.
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