Everything upstairs makes sense. What is said on the third floor is read directly from the book, and it can only be regarded as perceptual knowledge if it is accepted without the verification of its own thinking. There are too many personal emotional factors in the process of thinking, and it is also perceptual knowledge if it is not objective enough.

For example: 1+ 1=2, if someone teaches you this way, you will remember it and use it in the future, then this understanding is perceptual.

Then one day a mathematician told you that 1+ 1 is not equal to 2, and you learned from him how to prove that 1+ 1 is not equal to 2 mathematically. You know the principle, so when you see 1+ 1 in the future, you will say that it is not equal to 2. You think you are rational because you understand the reasons behind it. But this is actually perceptual knowledge.

Real rational understanding should be combined with objective reality and can change with the change of objective conditions, rather than sticking to one's own opinions. 1+ 1 equals 2 when it needs to be equal to 2. When you need to wait, you must be able to prove that it is not equal to 2. This shows that you have a rational understanding of it.