The separate articles here collected and selected are, partly lectures in exposition of philosophical theory, partly detailed psychological investigation and metaphysical research. The publication of the volume was in preparation when the war broke out and interrupted the work. The principle on which the articles are selected is indicated in the title, Mind-Energy. They are chosen by M. Bergson with the view of illustrating his concept that reality is fundamentally a spiritual activity. A second series is to follow illustrating his theory of philosophic method.

The subject title, Mind-Energy, will recall the title, Mind-Stuff, which W. K. Clifford in a lecture many years ago employed to denote a new theory of consciousness. Since that day a change almost amounting to a revolution has overtaken the general concept of the nature of physical reality. This is due to the development of the electro-magnetic theory of matter. In modern physics we may say that the old concept of stuff has been completely displaced by the new concept of radiant energy. An analogous change has gradually meanwhile pervaded the whole science of psychology. In recent years we have witnessed the opening up of a new and long-unsuspected realm of fact to scientific investigation, the unconscious mind. The very term seemed to the older philosophy to imply a latent contradiction, today it is a simple general description of recognized phenomena. Just as a dynamic concept of physical reality has replaced the older static concept in the mathematical sciences, and as this has long found expression in the term energy, so a dynamic concept of psychical reality has replaced the older concept of mind which identified it with awareness or consciousness, and the physical analogy suggests energy as the most expressive term for it. In affirming Mind-Energy the intention is not to include the activity of mind in the system of radiant energy which constitutes the science of physics.