Ancient metaphysics underwent many changes at the hands of medieval thinkers who brought it in line with the dominant religious and theological movements of their day.

The sciences which take socio-historical reality as their subject matter are seeking, more intensively than ever before, their systematic relations to one another and to their foundation.

From the perspective of mere representation, the external world always remains only a phenomenon.

The existence of inherent limits of experience in no way settles the question about the subordination of facts of the human world to our knowledge of matter.

A knowledge of the forces that rule society, of the causes that have produced its upheavals, and of society's resources for promoting healthy progress has become of vital concern to our civilization.

If we conceive all the changes in the physical world as reducible to the motion of atoms, motions generated by means of the fixed nuclear forces of those atoms, the whole of the world could thus be known by means of the natural sciences.

The individual always realizes only one of the possibilities in his development, which could always have taken a different turning whenever he had to make an important decision.