Edouard Manet, "Luncheon on the Grass," 1862-63. Oil on canvas, 82" x 105."
The cut and paste space of this picture is famously a precursor to abstract painting; the people and objects are arranged according to the artist's desired locations, and the accuracy of the perspective is abandoned to that end. Greenberg considers Manet the first modernist painter for this reason. But even as the picture ushers in a modernist approach to painting, it predicts the post-modern collage and the disjuncture and discontinuity it implies.
As if that wasn't enough, the painting is also reverential to the past, and not in a glib or ironic way; Manet's well-known love of Velazquez is stamped all over the picture. But the most cursory inspection shows that it couldn't possibly be a Velazquez - the strangeness of the perspective is a dead giveaway. Velazquez himself had a similar relationship to Titian; not specifically in terms of the perspective, but in the more general sense of a strong family resemblance subverted by aspects which could have not shown up in the earlier artist's work.
Manet's enthusiasm for Velazquez was not that different than the reverence that 19th century French academic painters had for Raphael (Thomas Couture, Manet's one-time teacher, is a good example). What Manet did with that reverence was utterly different, though. Rather than show his admiration by being a copyist, he sifted out the things he could use, left out parts that seemed dated, and added things that were germane to his moment in time and his own purposes.
The contemporary painter, especially the contemporary abstract painter needs to consider this model. Classicism is definitely not the way to go right now - an overly orthodox approach seems to me an excellent way to hasten the notorious death of painting as opposed to postponing it. But at the same time it would be a mistake to throw out the baby with the bath water.
Abstraction and modernism are not indissoluble, and in the end, that's a good thing.