A characteristic of scientific inquiry, distinguishing it from man's earlier ways of solving the riddles of the world, is that it admits as instruments of knowledge exclusively those activities of the human soul over which we have full control because they take place in the full light of consciousness. This also explains why there has been no science, in the true sense of the word, prior to the beginning of the era commonly called 'modern' - that is, before the fifteenth century. For the consciousness on which man's scientific striving is based is itself an outcome of human evolution.