on condition that only if

I told my captors I'd cooperate on the condition that I would only post the truth - if they wanted me to post anything false or withhold anything true, they'd have to kill me first.

我告诉那些绑架我的人，我愿意与人合作，但我只写事实的真相，如果有谁试图让我写任何虚假的事情，那得先杀了我。

We are so unfortunate that we can only take pleasure in a thing on condition of being annoyed if it turn out ill, as a thousand things can do, and do every hour.

我们是如此不幸，以至于只有在某件事难以处理、令人烦恼的情况下，才能得到快乐，成千上万的事情都是这样，我们时时都有事情可做。