To me, all art is abstract on many levels. Formally it's all abstraction in varying degrees. A friend of mine once said that his favorite abstract painter was Andrew Wyeth. That's a great observation, especially if you've ever noticed the elegance of those compositions and the expression in those free-flowing lines. Our egos get trapped in illusionism, though. Abstraction connects us to our universal psychic energy, while illusionism connects us to the ground. There's value in a balance of both, I think. Trees have accomplished that. People, not so much. In our effort to be like trees, we try to build glass towers into the sky, like Nimrod (or a nimrod).