First of all what do we see
What does a person or painter see first in the object he focuses on?
Does he see the shape?
Other form elements: Color, mass, texture, chiaroscuro, stain-line ..?
Which?
It sees two-dimensional shape.
Subsequently, the third dimension, space, that is, the massiveness of the object; he sees it.
In order to understand the discourse, we would like to give an example of geometric shape, cylinder.
When we focus on a white vertical cylinder with its short sides in the horizontal direction, we focus on it; we see the rectangular shape of the cylinder.
This is what we will see first.
It's a hollow rectangle! We see a two-dimensional hollow geometric shape.
A little later: We will notice that the shape - the shape, that is, the two dimensional surface, is defined to the depth. That is the depth of the third dimension; the ultimate seeing of the shades of light that does this and the CYLINDER itself!