Original nature decides this in part. Man is so constituted by nature that certain stimuli produce feelings of satisfaction and others discomfort. Sweet tastes, rhythmical sounds, movement after rest, relaxation of the muscles after fatigue, the moderate action of the senses of vision, hearing and smell, are thus satisfying to well nigh everyone. The free exercise of instinctive tendencies to take, hold, play, sleep, run, fondle and the like, is an almost equally important source of satisfaction. Sensory pains from blows, cuts, burns, diseases and the like; certain sensations and emotions such as hunger, thirst, fatigue, fear, anxiety; restraint from the exercise of instinctive tendencies, as by capture, confinement or the obstruction of movement, are for the same reason uncomfortable. Let us call these two classes of feelings, Original Satisfiers and Original Troublers.

Original nature alone is obviously insufficient to account for all likes and dislikes; for they differ much with different individuals, change much with age and alter quickly with training. Whether any given result shall be satisfying or uncomfortable depends in part upon what it has been associated with. The rule is that, other things being equal, any feeling will be satisfying which has been associated with original satisfiers, and that any feeling will be uncomfortable which has been associated with original troublers. Thus 'to have the bottle' becomes a satisfactory result to the baby, being suffused with the feeling originally felt only with the result 'food in mouth.' After the satisfyingness has been acquired from connection with an original satisfier, it can spread further. Later 'to see the bottle being brought' and later still 'to be told "You shall have your milk," ' acquire in turn this aura of satisfyingness. The discomfort of the blow spreads to the sight of the uplifted hand, and from there

to the sound of the spoken threat. No matter how barren or instinctive pleasurableness a condition may be, it may become the most cherished and satisfying of feelings. 'I am doing God's will,' 'I am serving the state,' and 'I am hunting the truth,' have ruled men's lives in spite of their lack of intrinsic satisfaction.

The general laws of instinct and of association thus account for the satisfying and uncomfortable qualities of different feelings as well as for the connections amongst stimuli, mental states and movements. How the satisfaction following upon a connection strengthens it, and how the discomfort following upon a connection weakens it, must be left unanswered questions. Neither psychology nor physiology has yet anything much better than a guess to offer to this, the most fundamental question of the mental life of man and of the animal kingdom as a whole. All that can be said is that the original satisfiers are as a rule events useful for the survival of the species and the original troublers are as a rule events disadvantageous to the survival of the species; consequently any means by which the former could reinforce the connections causing them and the latter weaken the connections causing them would, when evolved, be maintained by natural selection. Perhaps their respective influences on the blood supply constitute such a means.

§ 61. Conclusion of Part III

Complex as is a human life, it is at bottom explainable by a few principles. The presence of original tendencies to connections and of satisfaction and discomfort as qualities of certain feelings, the power of satisfaction to strengthen the connections producing it and of discomfort to weaken those producing it, the natural influence of frequency, recency and intensity on con

nections: these are the ultimate laws of dynamic psychology. Of these the only one unexplained by the general laws of living beings is the power of satisfaction and discomfort.

The development of a human mental life may be likened to that of the animal kingdom as a whole. The present animal kingdom is the result of the existence in the past of many variations, the elimination of those which did not fit the environment so as to survive, and the persistence of the others through heredity. The eliminating agent in this case is death. Any man's intellect and character are the results of the existence in his past of many connections, the elimination of those which did not fit their environment so as to bring satisfaction, and the persistence of the others through the law of association. The eliminating agent in this case is dissatisfaction and the environment is not the physical world alone but also the greater universe of passions and ideals, of wrong and right, of falsehood and truth.

It is often said that there is and can be no science of human nature, that it is impossible to do more than make shrewd guesses as the poets, story-writers and proverbmakers do. The progress of psychology is, however, gradually proving the assertion false. Even in the elementary and untechnical account of psychology presented in these few pages, there is given enough evidence to justify the faith that human life can be the object of systematic and verified knowledge. Nor are the facts of psychology so chaotic and fragmentary as is generally supposed. Although yet far from the perfection of full explanation by a few general laws which is being reached in the case of physical facts, they are nevertheless being more and more reduced to order and summarized under simple laws. In Part I the rich variety of human thought

and feeling was shown to be after all divisible into three natural groups: first, feelings of direct experience; second, reproductions of direct experience; and third, feelings meaning or referring to direct experience. In Part II the tremendously complex physical basis of mental life, the nervous system, was shown to be essentially the sum of the connections between sensitive areas of the body and motor organs, the same bodily organ, the neurone, being always the connecting agent. In Part III it has been shown that in great measure the intellects and characters of men are explainable by a single law, and that in the case of certain facts psychology possesses the final warrant of a science, the power to predict the future.

CHAPTER XXI

CONCLUSION: THE RELATIONS OF PSYCHOLOGY

§ 62. The Science of Psychology as a Whole

In this book only the more elementary and fundamental facts and laws of mental life have been presented. A complete account of the science of psychology would require many volumes. We have studied only the more general facts of ordinary human mental life, but psychology deals also with the details of sensations, the associations of ideas and the like, with the facts of abnormal and diseased minds and with the mental processes of animals. I have, as a rule, described only those facts which may be appreciated by simple observations and reflection, but psychology uses also, intricate analysis, elaborate experiments, exact measurements and wide comparisons. The subject matter of psychology covers a wide range of facts, and these are studied by many different methods.

Such a book as this can, of course, be but the slightest beginning of a study of psychology, of the thoughts and feelings of men, their relation to the nervous system and the human actions which they arouse and guide. The field of the science is so wide, and the methods of studying it so various that any one small book can present only the most general principles and offer only the simplest kind of an introduction to psychology as a whole. During the year 1903 alone there were published over two thousand