Aesthetics, which was not used as a term until after the 1750s, has been a matter of thoughtful discussion and disagreement for many centuries. The Greek philosopher Plato could, in fact, be considered the true originator of aesthetics because he spoke a great deal about the nature of beauty in several of his dialogues. For Plato, true beauty was an ideal beyond human perception; like truth and goodness, it was eternal. Beauty that was visible could not be absolutely beautiful, he believed, because it was subject to change, growth and decay. Beauty such as this was, in his judgement, merely an imitation of real beauty. For all that Plato said about beauty, his writings never give a precise definition of it. The Greek artists and artisans knew how they wanted to present beauty in such masterpieces as the Parthenon in Athens and the statue of Helios in Rhodes. They demanded proportion and harmony, in accordance with their principle of moderation: nothing too much or too little. But examples do not create definitions. During the late Middle Ages, St Thomas Aquinas tried to define beauty as “something pleasant to behold”. In imitation of the Greeks, he noted that, “Beauty consists in due proportion, for the senses delight in things duly proportioned.”