Over the centuries man's idea of what constitutes science has undergone profound changes. Ancient thinkers generally assumed that the power of reason was in itself sufficient to unravel all the secrets of nature with only a minimum of ference to actual facts. This type of philosophical reasoning did, in fact, reach some important conclusions as, for example, the atomic theory of Democritus and the heliocentirc astronomy or Seleucus. Early philosophers also reasined that ultimately a world state with equal opportunity would be necessary to satisfy the demands of justice