To understand philosophy, we must first understand the problems faced by philosophers. The background of Kant's question is like this. Mechanical materialism prevailed at that time. Everyone thinks that people are machines without soul and subjective initiative. People's thinking consciousness is determined by the hormones secreted. This idea leads to moral collapse. Because I kill people out of anger. Angry because the hormones in my body have nothing to do with me. This is unbearable for Kant. He believes that the concept that mechanical materialism interprets the world as completely determined by rational theorems leads to this moral concept. He wants to prove that reason and law cannot explain all phenomena, but to prove this, he must show that reason is not omnipotent. If reason is not omnipotent, then hormone determinism derived from reason is untenable. Criticism of pure reason is to prove that reason is not omnipotent. The specific method is this. Kant proved that reason needs materials, and the acquisition of materials needs human innate ability. Then he summed up the class 12, saying that this class 12 is the basis of cognition. Simply put, the blind can't reason with colors, and the deaf can't deduce sounds. So Kant's famous saying: Reason legislates for nature, which means that we can only know what our body functions allow us to know. The dimension of nature is infinite, while the dimension of human cognition is only 12, so reason can only know what is within this dimension 12, thus demonstrating that reason is not omnipotent, but has boundaries.