I N A U G U R A T I O N O F P H I L O S O P H Y C O U R S E S 9 6 9 TRANSLATION Professor Einstein Lectures at the Opening of Classes at the Faculty of Philosophy and Letters Lecture Effects of the Theory of Relativity on the Concepts of Space and Time The sage immediately occupied the stage, and despite the fact that his first words were an apology for not being able to express himself as clearly as he could in his native lan- guage, began his lecture in French, expressing himself with uncommon precision to a most enthusiastic response by those in attendance. Positivism and Idealism Today, said the sage, I will speak of philosophical matters. When I do so in German, I'm almost overcome by fear, he went on. I will also discuss other entertaining, if not amusing, mathematical matters, concepts and conceptual systems related to reasoning. And we will find ourselves obliged to consider matters having to do with experience, as well. In our times, he explained, there are two schools of thought regarding such issues: one is Positiv- ism and the other is Idealism. In Positivism, of which the majority of physicists are adher- ents, knowledge is based on experience, and concepts and conceptual systems are reached through induction. In a word, in Positivism it is believed that Truth originates in experience. In Idealism, on the other hand, one assumes the existence of truths that predate science, truths that are necessary to know in order to do science. Such a conception characterizes the Kantian school. Unlike what occurs in Positivism, in Idealism it is impossible to know the origin of concepts. In Positivism, he continued, as is well recognized,we must forge conceptual systems on the basis of experiential facts that will be sufficient to give us an idea of the things we ob- serve. If we were to be asked what must be required of concepts, Dr. Einstein added, we would say that there must be a relationship between them and the things we observe, and this should happen in a univocal way, for otherwise those concepts would not lead us clearly and unmistakably toward knowledge of the things of the outside world, from which, fur- thermore, they must originate. Geometry Let us now move on to geometry, said the sage. Euclidean geometry is that of intuitive space, constructed on certain postulates. If the relationships between its concepts and nat- ural objects are not established, either consciously or subliminally, we would have a struc- ture made of words, but with no real content. These relationships may be expressed directly or indirectly. This property is accentuated with the progress of science.