Reality is the most difficult thing for the human mind to grasp. This vital knowledge comes only from observation and experiment and the effort these require is repugnant to us. It is easier to read the papers, listen to the radio and go to the movies. Most people are incapable of close contact with themselves, with each other or, indeed, with anything at all. They are the victims of their education and their habits. Their only intellectual formation has been acquired by cramming far examinations. In the artificial life of the factory and the office, they have never looked reality in the face. They ignore the beauty of the virgin snow, the noonday hush on the still cornfields, the anguish of the sick in lonely farmhouses. They are incapable of observing exactly what happens in and about them. Yet the reality we need so desperately to know is not made up of notions picked up from books and newspapers but the immediate data of observation and experience. These data can only be used in the form of abstractions which remain very close to the concrete: as simple concepts belonging to the class of operational concepts we have mentioned before. Such concepts are as necessary to the conduct of life as to the progress of science. They are the only instruments which permit the mind to find its way in the real world with the certainty of instinct.

Reality has several aspects. They are created either by the technique employed in the analysis of phenomena or by the scale on which these observations are made. The techniques which reveal our spiritual activities, though far less precise, are just as important as those designed to analyze organic ones. Everything we know about the universe and about ourselves derives from two distinct sciences: that of the inorganic world where physics and chemistry overlap and that of life which includes psychology and sociology as well as anatomy, physiology and genetics. Whether we discover in man a material structure, physiological activities or intellectual and moral ones, depends on whether we are using the technique of anatomy, physiology or psychology. The most direct of all analytical techniques is introspection. The examination of the self by the self brings us face to face with something different from anything which has existed since the beginning of the universe; with an event which has never happened before and can never happen again. We come up against that thing at once fixed and changing, mysterious and familiar, material and spiritual, which is our-self. The vision of this unique being, arrived at by introspection, constitutes for us the most certain and least variable aspect of reality. Such observations are always made from the same point of view since the observer is himself the object observed. They are made direct, with no apparatus to increase or dimmish the clearness of vision. Although no microscope or telescope exists to explore our own consciousness, the habit of self-examination sharpens our insight. We gain a progressively profounder knowledge of the characteristics and particular trends of our own personality. All other aspects of reality, whether of our own bodies or of anything else in the physical world, can only be observed at second hand and at different and variable levels. The aspect of the same object varies according to the standpoint of the observer. The Statue of Liberty illuminating the world in New York harbor loses all significance if one sees it from too near or too far. Seen from its foot, it appears an almost shapeless mass of bronze. If one flies several hundred feet above it, both statue and island become a mere meaningless dot on the water. The skin of the face, seen by the painter, differs profoundly from what the anatomist sees when he examines it through a microscope. An observation made from a given point of view is neither more nor less true than that made from another. The idea of the blood which we derive from physicochemistry is not better than the one we derive from histology. One expresses the molecular aspect of the blood and the other the cellular. From the human point of view, blood is simply the red liquid which runs out when we cut ourselves. The ideas derived from observations on one plane are not always applicable on another. The principles of Euclid are true as regards the surface of the earth but not in the totality of the universe which appears to be non-Euclidean. The laws of pure mechanics do not apply to the interatomic world. A concept is only valid on the level from which it was derived.

Of what kind of reality, then, do we so urgently need knowledge to conduct our lives? Of reality on our own level, such as it presents itself to our ordinary experience. For us, the real aspect of a poplar tree is what we perceive when we walk in its shade, not what we see from an airplane high above its summit. Our cosmic universe is far closer to that of our ancestors who lived when the Gothic cathedrals were still white than to that of Planck, Einstein or Broglie. For us it is still true that the sun goes round the earth and that the earth is the center of the universe. What is real from our point of view are the joys and sorrows of daily life and human beings in all the circumstances of their passage through this world. Lovers walking in the moonlight, the mother smiling at her child, the peasant harnessing his oxen, the clerk scraping a living at his desk, the baby we once were and the corpse we shall one day be . . . these are real for us. Yet reality from our point of view stretches beyond the physical continuum, beyond the four dimensions of space and time into that immaterial world poets and saints have revealed to us. A hero's sacrifice has a beauty as vivid as that of sunrise on snowy mountains. Grace illuminates the face of one chosen by God with an interior light as real as that of dawn. Since, in fact, the world of matter is inseparable from that of spirit, we must learn to understand both. The laws we need above all to know are not those of the stellar or the interatomic universe but the fundamental tendencies of things as they are revealed to us on our own level by observation and experience. These constitute the aspect of reality which is essential for us to bear in mind in every circumstance of our lives.