The English copula becan be inflected in the past tense as was:
1a. He is a student. (Present tense)
2a. He was a student. (Past tense)
Such is not possible in Chinese, however, for two reasons. First, Chinese does not have tense, but only aspects, represented by aspect markers, such as le (perfective), guo (experiential), and zhe (continuative). Second, the Chinese copula shì cannot be used with aspect markers:
2. tā shì *le/*zhe/*guo xuéshēng
he be LE/ZHE/GUO student
Thus, the only way to express “he was a student” in Chinese is by context or adding additional words that clarify the context, as illustrated in (3-4).
3. tā yǐqián shì xuéshēng
he before be student
He was a student before.
4. nà shíhòu, tā shì xuéshēng
that time he be student
At that time, he was a student.
