1 6 2 D O C . 1 5 6 O N B A S I C C O N C E P T S O F P H Y S I C S 156. “On the Basic Concepts of Physics and Their Most Recent Transformation”[1] [Berlin, before 18 March 1928][2] Even though the world of our sensory perceptions reveals to us directly only vague interrelationships, and even though our actions appear to us to be completely free, i.e., not subject to objective natural laws, we still feel a need to regard all that occurs as necessarily & completely subject to regular laws (causal). This need is certainly a product of the intellectual experience that we have accumulated over the history of cultural development. Primitive peoples, in contrast, seek to reduce all events analogously to the effects of our own free will to the will of invisible spirits. The postulate of a strictly causal order of nature is thus by no means a given of the human psyche, but the result of a long process of mental adaptation. Trust in the perfect conformity to natural laws is based on the (at least modest) successes that have been achieved by human research in their conceptual mastery of natural events. This trust thus is by no means absolute in character. Even today, many object intuitively to the claim of an ineluctable causality. It is not easy for us to accept our own free decisions as being conditional on a strictly causal natural order, and to relinquish the belief in the spontaneity of our actions. The notion that “we can indeed do what we want, but we are forced to want what we must” is a bitter pill for human pride to swallow. And yet—who could deny that the majority of educated people in recent centuries has swallowed that pill & digested it com- pletely? In spite of being convinced that we could not master the practical details of life without the fiction of our free will, there is no serious threat from the phys- iological-psychological side that would oppose the doctrine of universal causality. In particular, empirical evidence for the effects of internally secreted substances on our psychological reactions, of hypnosis & of certain poisons on our psychological reactions have practically silenced opposition from that side. Today, the belief in an ineluctable causality is under threat from precisely those people to whom it originally appeared as a first & impeccable guide, that is, the rep- resentatives of physics.[3] In order to understand this tendency, which deserves the undivided interest of all thoughtful persons, we must consider the previous devel- opment of the fundamental concepts of physics from a bird’s-eye view. Science makes the attempt to understand the relationships between our sensory experiences, i.e., to propose logical constructions of concepts that make those re- lationships appear as logical consequences. The choice of such concepts & logical construction rules is intrinsically free. The justification for such free choice lies in its results alone, that is, that they can successfully explain the observed relation- ships. [p. 1] [p. 2]