History of Western Philosophy - Bertrand Russell [79]
The philosopher who is to be a guardian must, according to Plato, return into the cave, and live among those who have never seen the sun of truth. It would seem that God Himself, if He wishes to amend His creation, must do likewise; a Christian Platonist might so interpret the Incarnation. But it remains completely impossible to explain why God was not content with the world of ideas. The philosopher finds the cave in existence, and is actuated by benevolence in returning to it; but the Creator, if He created everything, might, one would think, have avoided the cave altogether.
Perhaps this difficulty arises only from the Christian notion of a Creator, and is not chargeable to Plato, who says that God did not create everything, but only what is good. The multiplicity of the sensible world, on this view, would have some other source than God. And the ideas would, perhaps, be not so much created by God as constituents of His essence. The apparent pluralism involved in the multiplicity of ideas would thus not be ultimate. Ultimately there is only God, or the Good, to whom the ideas are adjectival. This, at any rate, is a possible interpretation of Plato.
Plato proceeds to an interesting sketch of the education proper to a young man who is to be a guardian. We saw that the young man is selected for this honour on the ground of a combination of intellectual and moral qualities; he must be just and gentle, fond of learning, with a good memory and a harmonious mind. The young man who has been chosen for these merits will spend the years from twenty to thirty on the four Pythagorean studies: arithmetic, geometry (plane and solid), astronomy, and harmony. These studies are not to be pursued in any utilitarian spirit, but in order to prepare his mind for the vision of eternal things. In astronomy, for example, he is not to trouble himself too much about the actual heavenly bodies, but rather with the mathematics of the motion of ideal heavenly bodies. This may sound absurd to modern ears, but strange to say, it proved to be a fruitful point of view in connection with empirical astronomy. The way this came about is curious, and worth considering.
The apparent motions of the planets, until they have been very profoundly analysed, appear to be irregular and complicated, and not at all such as a Pythagorean Creator would have chosen. It was obvious to every Greek that the heavens ought to exemplify mathematical beauty, which would only be the case if the planets moved in circles. This would be especially evident to Plato, owing to his emphasis on the good. The problem thus arose: is there any hypothesis which will reduce the apparent disorderliness of planetary motions to order and beauty and simplicity? If there is, the idea of the good will justify us in asserting this hypothesis. Aristarchus of Samos found such a hypothesis: that all the planets, including the earth, go round the sun in circles. This view was rejected for two thousand years, partly on the authority of Aristotle, who attributes a rather similar hypothesis to 'the Pythagoreans' (De Coelo, 293 a). It was revived by Copernicus, and its success might seem to justify Plato's aesthetic bias in astronomy. Unfortunately, however, Kepler discovered that the planets move in ellipses, not in circles, with the sun at a focus, not at the centre; then Newton discovered that they do not move even in exact ellipses. And so the geometrical simplicity sought by Plato, and apparently found by Aristarchus of Samos, proved in the end illusory.
This piece of scientific history illustrates a general maxim: that any hypothesis, however absurd, may be useful in science, if it enables a discoverer to conceive things in a new way; but that, when it has served this purpose by luck, it is likely to become an obstacle to further advance. The belief in the good as the key to the scientific understanding of the world was useful, at a certain stage, in astronomy, but at