I always knew, from my studies of Japanese, that the number two is 二 (èr). I am not sure about the actual etymology, but looking at the character, it's understandable why it represents the number "2".
Recently, I discovered that there is another character that represents the same number. That character is 两 (liăng).
According to my textbook:
- 二 is used when telling or writing a "meaningless" number, such as a telephone number, a zip code, etc;
- 两 is used together with nouns, such as in "two students" = 两个学生.
Is this correct in current Mandarin? If so, does this mean that 二个学生 is just plain wrong or that Chinese people would give me a weird look if I said it?
Are there other situations in which the use differs or is it interchangeable? I found a site, nciku.com, where there are notes about it, but it says what I already know more or less, so I am asking if there is something else.
Lastly, what's the etymology, if available, for 两?