Francesco Albani's Galatea in Her Shell Wagon, above left, is emblematic of classicism, which seeks an idealized standard of perfect beauty. Guercino's Saint Luke, on the right, is an example of naturalism, which aims for a faithful portrayal of the real world.
With her perfectly proportioned face and body, Galatea floats above the water—a model of ideal beauty. Classicism rested on two premises: that the classical art of ancient Greece and Rome (plus the High Renaissance) set the standard for all future achievement, and that the representation of the real world can be improved by eliminating everything irregular, transitory, and inconsequential—creating an idealized portrayal of nature not as it is, but as it should be.
Saint Luke, on the other hand, is presented to us as real person, lost in thought at his workbench with wrinkled forehead, his paintbrushes and palette in hand. Artists following naturalism cultivated such convincing visual effects that correspond as closely as possible to the experience of the viewer. The goal was to copy nature faithfully, whether it seems ugly or beautiful.