Such progress is a question of time. Atheism in a psychological sense began with the beginning of physical science. Pure Theism, in its early form of polytheism, saw in all natural movements and forces the expression of a personal power or powers, analogous to man; and its gods were and are simply magnified projections of humanity. Thus the sun, moon, and planets, the winds, the thunder, the lightning, the rivers, the fountains, the seas, were all figured as ruled and moved by personal deities. As soon, however, as astronomy made certain the perfectly regular movements of the sun and stars, Theism was to that extent logically limited, and Atheism to that extent logically possible. Astronomy was strictly godless in so far as it showed the universe to move by undeviating law. Of course this perception is but a small part of human consciousness and daily life; and the habit of theising, so to speak, easily overrode the habit of atheising. But every advance in exact knowledge of Nature, and in the capacity for exact thought, tended to encourage the atheistic view, and to discredit the theistic. Hence the spread of Atheism and Agnosticism among the Greeks in their progressive and scientific period. It needed the constant reform and modification of theistic doctrine, and later the complete arrest of all scientific thought, to keep the theistic view of things in power and place. And there had to be a revival of science and exact thinking before there could again be talk of Atheism.