They talked about the real world that is outside, that is dirty,impure,profane versus academia, which is lofty,idealistic,sacred.

他们将外面的世界看成是现实，是肮脏的，不洁，被亵渎的，而学术界，则是崇高的，有理想的，神圣的。

哈佛公开课 - 幸福课课程节选

So with the problems, that is where you really will get your hands dirty and truly immerse yourself in this world of computer science and programming.

带着这些问题，你就能深入研究,这真的可以使你沉浸到计算机科学,和编程世界中。

哈佛公开课 - 计算机科学课程节选

Then they notice that their toilet is kind of dirty.

然后他们发现马桶脏了。

耶鲁公开课 - 心理学导论课程节选

You might say,the only way to explain the behavior is to say that at some level, he really does believe his hands are dirty, despite the fact that he says they're not.

唯一的解释也许就是，在某种程度上，他确实还是相信自己的手脏的，尽管他说它们不脏。

耶鲁公开课 - 死亡课程节选