Taking 1+2 as an example, it is hard to see why the concept of 1 plus the concept of 2 equals the concept of 3, so intuition or experience is needed. For example, 1 apple plus 2 apples can be equal to 3 apples. However, we can see that this formula has the inevitability of "surpassing" experience, because even without intuition and experience, this formula is also valid. So this is an innate comprehensive judgment. And the straight line between two points in geometry is the shortest straight line. From the concept of straight line, we can't see the short, we can only rely on intuition, but this is generally effective (that is, it is accurate without experience and intuition). The difference between prior knowledge and prior knowledge is that prior knowledge must be innate, but prior knowledge is not necessarily prior, which is why I have answered prior for a long time. But the innate comprehensive knowledge is not a priori. Your question is divided into two levels: mathematics comes from experience, but why is it "innate"? What does Kant mean by "innate"? The answers to these two questions are in the preface and the first part "Transcendental Perception" of Critique of Pure Reason. Kant spent dozens of pages on these two issues. Personally, I feel that it is difficult to get a reliable answer to this question on Zhihu. Read a book. The following are the pure batch's answers to these two questions, and I will try to describe them briefly. For the second question, what does "congenital" mean? Knowledge independent of experience and all feelings and impressions is called innate knowledge. You may not be satisfied with this answer. Kant spent a long time explaining this sentence. For example, what knowledge belongs to innate knowledge and what belongs to empirical knowledge has long been left to the subject to explore in pure batches. For the first question, "Why is mathematics born?" First of all, Kant's mathematics in his time only included "algebra" and "geometry". This historical limitation has been broken today, but it is not important. There are only two elements in Kant's transcendental element theory, namely "time" and "space", that is to say, people's understanding of time and space is transcendental perceptual. People's transcendental perceptual knowledge of space makes geometry possible, and people's transcendental perceptual knowledge of time makes algebra possible (Kant's view: 1+ 1=2 makes the innate comprehensive judgment possible entirely because of people's intuitive understanding of the infinite passage of time).