In my experience a painting is not made with colours and paint at all. I don't know what a painting is; who knows what sets off even the desire to paint? It might be things, thoughts, a memory, sensations, which have nothing to do directly with painting itself. They can come from anything and anywhere, a trifle, some detail observed, wondered about and, naturally from the previous painting. The painting is not on a surface, but on a plane which is imagined. It moves in a mind. It is not there physically at all. It is an illusion, a piece of magic, so what you see is not what you see.... There is Leonardo da Vinci's famous statement that painting is a thing of the mind. I think that's right. I think that the idea of the pleasure of the eye is not merely limited, it isn't even possible. Everything means something. Anything in life or in art, any mark you make has meaning and the only question is, 'what kind of meaning?'
-- Philip Guston, from "Philip Guston Talking" (lecture given at the University of Minnestoa, March 1978)Guston here is talking about the idea of painting, rather than the existence of some physical materials on a canvas that make a beautiful image. That is the true nature of painting -- it is formed in the mind. The witness to beauty and the sublime connection we may feel with a certain painting is about the mind's connection to that idea -- it's not a visual connection but an emotional connection that makes a painting visually compelling. The meaning behind the painting is what makes the painting, especially when we are talking about abstract painting. A painter's philosophy made manifest is what abstract painting is all about. A painting is a living thing, it "moves in a mind."