The fundamental concepts of my psychology have been set forth in the course of this book.

Helped by the perceptive translation of M. Cahen-Salabelle, the reader will not have failed to take note that this psychology does not rest on academic postulates, but on my experiences of man, in health and in sickness.

That is why it could not be confined to a study of the contents and functions of consciousness: it had to concern itself also with that part of the psyche we call the unconscious.

Everything we say about the unconscious should be taken with a grain of salt; we have only indirect evidence for its existence since it is not open to direct observations; whatever conceptions we form of it are but logical deductions from its effects.

These deductions possess only a hypothetical validity because it cannot be determined beforehand whether the nature of the unconscious can be adequately grasped by the conscious mind.

I have always endeavoured, therefore, to find a formulation which brings together in a logical relationship the greatest possible number of observed facts, or else, on the basis of my knowledge of a given psychic state, to predict its probable future development, which is also a method for proving the correctness of a given hypothesis.

Many a medical diagnosis, as we know, can hardly be proved right at the moment the doctor formulates it, and can be confirmed only when the disease takes its predicted course.

It is in this way that my views concerning the unconscious have little by little been built up.

It is my conviction that the investigation of the psyche is the science of the future.

Psychology is the youngest of the sciences and is only at the beginning of its development. 

It is, however, the science we need most.

Indeed, it is becoming ever more obvious that it is not famine, not earthquakes, not microbes, not cancer but man himself who is man’s greatest danger to man, for the simple reason that there is no adequate protection against psychic epidemics, which are infinitely more devastating than the worst of natural catastrophes.

The supreme danger which threatens individuals as veil as whole nations is a psychic danger.

Reason has proved itself completely powerless, precisely because its arguments have an effect only on the conscious mind and not on the unconscious.

The greatest danger of all comes from the masses, in whom the effects of the unconscious pile up cumulatively and the reasonableness of the conscious mind is stifled.

Every mass organization is a latent danger just as much as a heap of dynamite is.

It lets loose effects which no man wants and no man can stop.

It is therefore in the highest degree desirable that a knowledge of psychology should spread so that men can understand the source of the supreme dangers that threaten them.

Not by arming to the teeth, each for itself, can the nations defend themselves in the long run from the frightful catastrophes of modern war.

The heaping up of arms is itself a call to war.

Rather must they recognize those psychic conditions under which the unconscious bursts the dykes of consciousness and overwhelms it.

It is my hope that this book will help to throw light on this fundamental problem for mankind. ~Carl Jung, CW 18, Pages 589-590