Pythagoras school also uses natural numbers to symbolize intangible things. For example, 1 stands for soul or reason (because it is the most basic number), "2" stands for opinion (because it is vacillating), "4" and "9" are justice (because they are the squares of the first even number "2" and the first odd number "3" respectively), and "5" is marriage (because Bi Bi. For example, they think that the number of celestial bodies should be 10 (perfection and harmony), so in order to meet the needs of harmony, they invented an imaginary celestial body-"to the earth" in addition to the nine celestial bodies they observed.