Why do mathematical Platonists consider numbers to be independent of human minds?

Mathematical Platonists consider numbers to be independent of human minds because they define numbers as abstract objects. According to this view, these objects are entirely nonmental, nonphysical, and nonspatiotemporal, meaning they exist outside of space, time, and human consciousness.123

Platonists argue that having a mental idea of a number—such as the number 4—does not make that number a mere mental construct. They draw an analogy to the Moon: just as people have ideas of the Moon in their minds without the Moon itself being a mental idea, numbers are real, objective entities that exist independently of human thought.12

Because these objects are nonphysical and exist outside the physical universe, they are considered unchanging and eternal. Consequently, Platonists view mathematics not as a human invention, but as the study of these objective, abstract structures, much like how astronomers study the solar system as an existing, external reality.12