He says he believes it is necessary to let North Korea know having nuclear programs will prove to be a bigger disadvantage than not having them.

VOA: standard.2009.05.26

It's not necessary to do that, but it can be quite convenient.

虽然没有必要这样做，但是这样做是很方便的。

麻省理工公开课 - 热力学与动力学课程节选

We've extrapolated that people have property rights and so whether or not it would be a good thing or a nice thing or even a necessary thing for the survival of some people, we don't see that that justifies the violation of the right that we've logically extrapolated.

我们已经推出人们有财产权,所以，就算是为了做好事，做善事,甚至是为了让某些人活下去而必须做的事，那也是不能证明，侵犯这些推定的权利,就是正当的。

耶鲁公开课 - 公正课程节选