Theory of forms
Platonic idealism also explains that it is impossible for us to perceive these forms through our senses, like our sense of hearing or sense of seeing. The only way we can truly understand a form is through the use of logic and mathematics. Through mathematics, we have discovered the form of the triangle: a polygon with 3 sides. However we will never be able to truly see with our eyes such a triangle. Even if we tried to draw it on a whiteboard with a ruler, it's lines will never be perfectly straight and two-dimensional.