Professor Gordy has well said on this point: "The mind must either be _that which_ thinks, feels, and wills, or it must be the thoughts, feelings, and acts of will of which we are conscious--mental facts, in one word. But what can we know about _that which_ thinks, feels, and wills, and what can we find out about it? Where is it? You will probably say, in the brain. But, if you are speaking literally, if you say that it is in the brain, as a pencil is in the pocket, then you must mean that it takes up room, that it occupies space, and that would make it very much like a material thing. In truth, the more carefully you consider it, the more plainly you will see what thinking men have known for a long time--that we do not know and cannot learn anything about the thing which thinks, and feels, and wills. It is beyond the range of human knowledge. The books which define psychology as the science of mind have not a word to say about that which thinks, and feels, and wills. They are entirely taken up with these thoughts and feelings and acts of the will,--mental facts, in a word,--trying to tell us what they are, and to arrange them in classes, and tell us the circumstances or conditions under which they exist. It seems to me that it would be better to define psychology as _the science of the experiences, phenomena, or facts of the mind, soul, or self--of mental facts, in a word_." In view of the facts of the case, and following the example of the best of the modern authorities, in this book we shall leave the consideration of the question of the ultimate nature of mind to the metaphysicians, and shall confine ourselves to the _mental facts_, the laws governing them, and the best methods of governing and using them in "the business of life." The classification and method of development to be followed in this book is as follows:-- I. The mechanism of mental states, _i.e._, the brain, nervous system, sense organs, etc. II. The fact of Consciousness and its planes. III. Mental processes or faculties, _i.e._, (1) Sensation and Perception; (2) Representation, or Imagination and Memory; (3) Feeling or Emotion; (4) Intellect, or Reason and Understanding; (5) Will or Volition. Mental states depend upon the physical mechanism for manifestation, whatever may be the ultimate nature of mind. Mental states, whatever their special character, will be found to fit into one of the above five general classes of mental activities. CHAPTER II. The Mechanism of Mental States.