In general, there are different usages for “二” and “兩” in noun, adjective, verb and adverb aspects. “二” has a different level of gradation in meaning than “兩”, such as the sequence of the events and the priority.
The Chinese learners are confused about the usage of “第二年” and “兩年”. As both “二“ and “兩“ presented before 年 which means year, they may consider both usages may be the same. However, it conveys a totally different meaning. “第二年” only shows the time point of an event and represents the spoken time which is equal to “In the second year” in English. Nevertheless, “兩年” is related to “two years” which brings out the continuity and duration of the event. It will be used to illustrate the previous activities and the current situation. To conclude, the difference is that “第二年” implies the individual has been doing such event or activity for a year while “兩年” implies the individual has been doing such event or activity for two years already and he/she is about to continue such event or activity for the third year.
We also found that “二” is used to represent in the form of numbers such as data. Examples are: “第二名選手” “第二位” “第二次來香港”. Therefore, “二” can act as an adjective to modify the noun, events or sequence. Besides, “二” itself belongs to a morpheme which can be a word itself or it can be used with quantifiers to form a word. It is related to the example above:五月二號, 他住在二樓.
As for the second usage, “二” also acts as a noun to show the numeral and the example is “二千萬二百二十二點零二”. However, amendments need to be made when the situation refers to writing a check-in Chinese. In English, its numeral value is twenty-two million and two hundred and twenty-two point two. Chinese numerals are required. Therefore, the written form in the check will be “貳千萬貳百貳十貳點零貳”, instead of Arabic numerals, Chinese numerals can avoid the problem of being amended easily by others and taking wrong numeral values. In addition, all decimal points are expressed in “二”, which “兩” is not accepted, such as “0.2”, “15.2”, also named “零點二”, “十五點二”.
“兩” always appears in the form of collocations with quantifiers (量詞) as suffixes. It can be applied individually and also be considered as lexis instead of morphemes. In terms of usage, numeral quantifiers are always formed with “兩” and eventually structured as numeral-classifier structures. Example: 班上總共有兩個人沒交功課。More examples are “請問幾多位？兩位，謝謝。” “兩對筷子，唔該。”. Furthermore, “兩” also named “両”, which is also a kind of quantifier for measurement. It is a unit that has been continued from East-Asian and existed long before the Han Dynasty. It is widely applied in different regions such as Vietnam, Japan and the Korean Peninsula. 1 gram “1斤” is equivalent to 16 tael “16兩”. It is commonly used in the measurement of jewellery in Hong Kong and Macau. And the Chinese idiom “半斤八兩” is also derived from that, which represents the value of “half a gram, equivalent to 8 taels” for literal understanding in English.
There is a special case in which both “兩” and “二” can be used for the measurement, examples are 兩克白糖、二十三厘米、兩茶匙. While expressing figures smaller than ten, we will use “兩” to indicate the meaning of two in the example of “明天的温度是兩度”. Yet, if we describe the number over twenty, we may use “二十” which the above example “明天的温度是二十二度”.
Apart from the above daily usage of “二” and“兩”, we can observe that there are different usage in Chinese idioms and expressions.
There are lots of idioms or classical Chinese that related to “二”, for example, “左傳 僖公十五年：「必報德，有死無二。」”; “君命無二”；”貴賤無二”. The above expressions are embedded with “二”, which means change. In this case, “二” can be used as a verb in old Chinese.
While “兩” can act as an adverb to express the meaning of both sides, each other or mutually in the literary language used in old Chinese. For instance, “兩敗俱傷”, “模棱兩可”, “三國志˙卷十˙魏書˙荀攸傳：「今兄弟遘惡，此勢不兩全。」” .