ince the former doc- trine about the proper way to form conceptions, to the effect that agreement with antecedent properties determines the value or validity of ideas, was the doctrine common to all philosophic schools except the pragmatic one of Peirce the logical and philosophical transformation thus affected may be said to be more far-reaching than even the extraordinary de- velopment in the content of natural science which resulted. It is not too much to say that whatever should be future develop- ments in discoveries about light, or that even if the details of the Einstein theory of relativity should be some time dis- credited, agenuine revolution, and one which will not go back- ward, has been effected in the theory of the origin, nature and test of scientific ideas.