We know they can't sign a legal agreement, but let's take that off the table.

我们都知道不能签署违法合同,那就只能私底下签协议了

耶鲁公开课 - 博弈论课程节选

Well if you have a slave, that slave can't actually sign contracts.

如果你有一个奴隶，但法律规定奴隶不能签署合同。

耶鲁公开课 - 新约课程节选