Since human beings have known the quantity of things, knowing that there are not only qualitative differences, but also quantitative differences, people have begun to express the quantity of things. For example, for 1 sheep+1 sheep, or 1 stone+1 stone and so on. The number obtained is represented by 2.
Of course, you can also use other symbols to represent quantities, such as two in Chinese, two in Arabic, or two in English, and so on. As for why 1+ 1 is not 3 or something else? Because 3 is used to represent quantities greater than 1+ 1.
Axiom is the conclusion that people generalize or define the world on the basis of their own understanding, and it is directly accepted by human beings without computational reasoning.
The problem of 1+ 1 in number theory discussed by many people upstairs is not the same as the problem of 1+ 1=2 in mathematics.
The problem of 1+ 1 in number theory refers to Goldbach's conjecture: "Any even number greater than 4 can be expressed by the sum of two odd prime numbers." In mathematics, people use 1+ 1 to represent the sum of two odd prime numbers, so some people use 1+2 to represent the sum of the products of one odd prime number and the other two odd prime numbers (for example, 22=7+3*5).
This expression is sometimes mistaken for "Mathematicians are proving 1+ 1=?" 1+2=? "Yes.
Mathematicians have proved the problem of 1+2, but we haven't completely proved the problem of 1+ 1 until now, although many mathematicians will work hard for it all their lives. It is estimated that there is still a long way to go to completely prove 1+ 1.
As mentioned above, "the problem of 1+ 1=2 in mathematics" is not a problem.