庄子与惠子游于濠梁之上。庄子曰:“鲦鱼出游从容,是鱼之乐也。”惠子曰:“子非鱼,安知鱼之乐?”庄子曰:“子非我,安知我不知鱼之乐?”惠子曰:“我非子,固不知子矣;子固非鱼也,子之不知鱼之乐,全矣!”庄子曰:“请循其本。子曰‘汝安知鱼乐’云者,既已知吾知之而问我。我知之濠上也。[1]
A rough translation:
A: Wow, look at the way the fishes are swimming! They must be happy!
B: You are not the fishes, how do you know that they are happy?
A: You are not me, how do you know that I don't know that I know that the fishes are happy?
B: I am not you, so I can't understand you; but you aren't the fishes, so you can't tell if they are happy or not. That makes sense.
A: Let's go back to the original premise. You are asking me "How do you know that they are happy", implying that you know that I know that they are happy. As to how I know, I know it because I am looking at the fishes right here and right now.
This is an excerpt from an actual Chinese classic, and it is written into the textbook. Happy or sad, this excerpt isn't meant to teach how semantical K's work.