According to roman law, why is slavery legal?

According to Roman law, slaves that were freed (libertinus, in regard to his master libertus) became Roman citizens, but they had many fewer rights than Roman citizens that were born free (ingenuus).

Explanation:

productive most commonly means: achieving or producing a significant amount or result.

explanation:

productive can also mean:

these depend on how the word productive is used. most likely productive will mean   achieving or producing a significant amount or result.