To many persons the words “consciousness” and “mental process,” or “thought” are regarded as synonymous.  And, in fact, psychologists so held until quite recently.  But now it is generally accepted as a fact that mental processes are not limited to the field of consciousness, and it is now generally taught that the field of sub-consciousness (that is, “under” conscious) mentation, is of a much greater extent than that of conscious mentation.

Not only is it true that the mind can hold in consciousness but one fact at any one instant, and that, consequently, only a very small fraction of our knowledge can be in consciousness at any one moment, but it is also true that the consciousness plays but a very small part in the totality of mental processes, or mentation.  The mind is not conscious of the greater portion of its own activities—­Maudsley says that only ten per cent comes into the field of consciousness.  Taine has stated it in these words:  “Of the world which makes up our being, we only perceive the highest points—­the lighted up peaks of a continent whose lower levels remain in the shade.”

But it is not our intention to speak of this great subconscious region of the mind at this point, for we shall have much to do with it later on.  It is mentioned here in order to show that the enlargement or development of consciousness is not so much a matter of “growth” as it is an “unfoldment”—­not a new creation or enlargement from outside, but rather an unfoldment outward from within.

From the very beginning of Life—­among the Particles of Inorganic Substance, may be found traces of something like Sensation, and response thereto.  Writers have not cared to give to this phenomenon the name of “sensation,” or “sensibility,” as the terms savored too much of “senses,” and “sense-organs.”  But Modern Science has not hesitated to bestow the names so long withheld.  The most advanced scientific writers do not hesitate to state that in reaction, chemical response, etc., may be seen indications of rudimentary sensation.  Haeckel says:  “I cannot imagine the simplest chemical and physical process without attributing the movement of the material particles to unconscious sensation.  The idea of Chemical Affinity consists in the fact that the various chemical elements perceive the qualitative differences in other elements and experience ‘pleasure’ or ‘revulsion’ at contacts with them, and execute their specific movements on this ground.”  He also speaks of the sensitiveness of “plasm,” or the substance of “living bodies,” as being “only a superior degree of the general irritability of substance.”