What you said above is wrong. The movement allocation of sonatas is the result of the development of music history. It is a basically fixed writing mode. It is generally divided into three movements. There are also special cases. There is basically no movement between the three movements. Connected, the three movements are distributed in the order of fast-slow-fast, and there is a fixed pattern. Sonata is just a form of music, that is to say, you divide it into three movements, arranged in the order of fast-slow-fast (such as Allegro Allegro-- Andante - dance music) is called a sonata.

If you want to know more, it will be helpful to take a look at the evolution of European music genres and forms.