Isn't the distinction between friend and enemy ? based on a kind of knowledge, on a perception of ? who is your friend and who is your enemy?

朋友与敌人之间的差别,不是根据知识吗，或是你对,谁是朋友或敌人的看法？

耶鲁公开课 - 政治哲学导论课程节选

One says, aim at your enemy and fire like this.

一种是,直接瞄准敌人,像这样射击

耶鲁公开课 - 基础物理课程节选

What he means, for instance, in this case is well, talking to yourself is self-reinforcing or giving bad news to an enemy is reinforcing because it makes your enemy feel bad.

比如在这个例子中，他的意思其实是，自言自语是种自我强化行为,而向敌人散布坏消息也是一种强化,因为这样做可以使敌人感到不快。

耶鲁公开课 - 心理学导论课程节选

Then it lands on your foot, because assuming the cannon is at zero height, the cannonball certainly comes out towards the enemy, but has no time of flight.

然后它就会落在你的脚边,因为假设大炮的高度为 0,炮弹笔直地出膛打向敌人,却没有时间飞行

耶鲁公开课 - 基础物理课程节选