The contract has to specify what are the causes of, let's say, death or a situation in which one is covered.

合约中必须指明,合约建立目的，比如说，死亡或者承保的是什么情况。

耶鲁公开课 - 金融市场课程节选

So I wasn't under a contract but let's come back and fulfill that promise anyway.

虽然我们没立下合同,但是我们以后会回来履行这个承诺的

耶鲁公开课 - 博弈论课程节选