IT WOULD be folly for you to approach this subject, about which there exists such wide-spread confusion of thought, without a prior study of basic principles. You cannot discriminate intelligently among these different conclusions without first formulating in your own mind the rules by which you are to be guided in arriving at a decision.

You must put every theory of the subconscious, or, in more scientific language, every conception of the subconscious, to the test of conformity with the methods of science. To do this you must first frame your test.

It is universally recognized that no theory or conception can be regarded as truly scientific or justifiable unless it contains certain well-defined elements.

The thing to do now, therefore, is to find out what elements must enter into a conception of the subconscious before that conception can be regarded as truly scientific.

You can then put these elements together into a conceptual model, and by this model as a standard of truth you may test the various theories of the subconscious.

The words "science" and "scientific" are commonly regarded as having a much more restricted meaning than rightfully belongs to them. Men talk of "the sciences," having in mind only mathematics, chemistry, physics, those sciences which have to do with the phenomena of matter.

As a matter of fact, any branch of classified human knowledge is a science, the term being just as applicable to one department of the classified facts of human experience as to another. Mathematics is no more truly scientific than history. The historian, if he pursues his researches in a scientific manner, is bound by the same rules as is the mathematician.

That which distinguishes science on the one hand from speculation, from religious philosophy on the other, is not the nature of its facts, but the method used in their investigation.

Whatever the problem may be, whether it arises in the study of chemistry or astronomy or language or history, whether it relates to mind or matter, actual experience must furnish the only elements that may scientifically be employed in its solution.

Science deals solely with the facts of human experience. These facts it submits to the two basic processes of Classification and Generalization.

The scientist classifies all the facts relating to his problem into sequences. That is to say, he groups together as evidence all of the known instances in which one event, "B," follows upon another, "A." From such a collection of sequences, the investigator deduces a general principle.

And if this general principle is properly accredited - that is to say, if in a vast number of instances "B" invariably follows upon "A," and the utmost research has failed to reveal a single instance in which "B" does not follow upon "A" - then this principle is recognized as a Scientific Law.

Now, these generalizations or laws are not expressed in terms of actual things. They contain no reference to physical realities that anyone ever actually heard or felt or saw.

They are written in the broadest form possible.

They are written in symbolic terms, representing the essential character of things - that is to say, in terms not of things, but of qualities of things. The terms in which such laws are expressed stand for purely abstract conceptions.

Take, for example, the law of gravity, "any particle attracts any other particle," a "particle" being defined as an infinitely small portion of matter. Or consider the modern scientific theory that every atom is composed of "electrons," each revolving in its own tiny orbit about a central point. Now, New-ton, who framed the law of gravity, never saw a "particle," nor has any man ever seen or otherwise had sensory knowledge of an "electron." The "electron" and "particle" are, in other words, imaginary things, abstract ideas, theoretical conclusions, arrived air by reducing sensory experiences to their essential qualities.

The ether, of whose "waves" and "vibrations" physics has so much to say, is of precisely similar character. In a way, it actually does violence to all our experiential knowledge of physical things, for it is imagined as having neither weight nor friction.

So, too, the "points" and "lines" of geometry are imagined as being without substance and as occupying no space.

In other words, the "particle," the "ether," the "line," the "point," are none of them concrete realities.

Like the letters of algebra, they are merely symbolic terms employed by the scientist in the solution of his problem. They are physical facts reduced to their theoretical or conceptual essence and are therefore technically known as concepts.

The value of the whole system lies in the fact that by it we are enabled to deduce from the facts of experience laws of such general application that we may apply them to the widest possible variety of appropriate facts, and in this way predict future events.

Now, what may constitute the essence of a given fact of experience depends altogether upon the point of view of the investigator. It depends upon the purpose or subject of the investigation.

The essential factor for one may be of no consequence to another. The petal of a rose to a geometrician is an irregular solid bounded by curved surfaces. To the chemist it is an aggregate of atoms. To neither is it a living thing of fragrant beauty.

In other words, the same fact may be differently conceived according to the point of view. Each investigator sees that element only which is pertinent to his own scientific aim. The concept of one may be just as valuable as the concept of another. Each is of value only in its own field of research.

In an earlier volume we pointed out that all our knowledge comes to us through the senses. The senses are our only means of communication with the outer world. All experience is sensory experience. All the facts of experience are in the last analysis merely sense-impressions.

Sense-impressions are the sole material of modern science. No scientific man, whatever his subject, considers that he is dealing with "things in themselves." He is perfectly aware that sense-impressions are the only realities, the only things of which he has or can have direct knowledge, and that the world for him as for everyone else is a mental world.

What, then, do scientists, psychologists and physicists mean when they speak of material or physical things as distinguished from mental, when they distinguish between mind and matter?

The answer is this: The psychologist and the physicist have entirely different scientific conceptions. They look at the world from two different points of view.

Each selects from his facts those elements and adopts those conceptions that are suited to his needs. The physicist is writing a story of the world of experience in terms of motion and structure. The psychologist is writing the story of the world of experience in terms of ideas, emotions and impulses.

Consequently, when you come to devise mental concepts and enunciate mental laws, you must confine yourself to mental terms. You must not invade, for example, the field of physiology. You must not frame your laws in terms drawn from the dissecting-room. You must not try to get down to the essential qualities of brain and nerve tissue.

When you find that the awakening of an idea in memory brings with it certain muscular activities, you must conceive them as resulting not from the potential physical energy in the nucleus of a brain cell, but from the potential mental energy of an idea.