The molecular changes incident to a sensation leave permanent traces, which are the physical bases of memory. One or several such remembered sensations, evoked by a present sensation, combine with it to form an Emotion. Characteristic of their origin is it that the emotions fall naturally into a dual classification, in which the one involves pleasurable or elevating, the other painful or depressing conditions. Thus we have the pairs joy and grief, hope and fear, love and hate, etc.
The question of pleasure and pain is thus seen to be the primary one of mental science. We must look to it to explain the meaning of sensation as a common quality of organism. What is the significance of pleasure and pain?
The question involves that of Life. Not to stray into foreign topics, it may broadly be said that as all change resolves itself into motion, and, as Helmholtz remarks, all science merges itself into mechanics, we should commence by asking what vital motions these sensations stand for or correspond to.
Every organism, and each of its parts, is the resultant of innumerable motions, a composition of forces. As such, each obeys the first law of motion, to wit, indefinite continuance of action until interfered with. This is a modification of Newton’s “law of continuance,” which, with the other primary laws of motion, must be taken as the foundation of biology as well as of astronomy.[11-1]
The diminution or dispersion of organic motion is expressed in physiological terms as waste; we are admonished of waste by pain; and thus admonished we supply the waste or avoid the injury as far as we can. But this connection of pain with waste is not a necessary one, nor is it the work of a Providentia particularis, as the schoolmen said. It is a simple result of natural selection. Many organisms have been born, no doubt, in which waste did not cause pain; caused, perhaps, pleasure. Consequently, they indulged their preferences and soon perished. Only those lived to propagate their kind in whom a different sensation was associated with waste, and they transmitted this sensitiveness increased by ancestral impression to their offspring. The curses of the human race to-day are alcohol, opium and tobacco, and they are so because they cause waste, but do not immediately produce painful but rather pleasurable feelings.
Pain, as the sensation of waste, is the precursor of death, of the part or system. By parity of evolution, pleasure came to be the sensation of continuance, of uninterrupted action, of increasing vigor and life. Every action, however, is accompanied by waste, and hence every pleasure developes pain. But it is all important to note that the latter is the mental correlative not of the action but of its cessation, not of the life of the part but of its ceasing to live. Pain, it is true, in certain limits excites to action; but it is by awakening the self-preservative tendencies, which are the real actors. This physiological distinction, capable of illustration from sensitive vegetable as well as the lowest animal organisms, has had an intimate connection with religious theories. The problems of suffering and death are precisely the ones which all religions set forth to solve in theory and in practice. Their creeds and myths are based on what they make of pain. The theory of Buddhism, which now has more followers than any other faith, is founded on four axioms, which are called “the four excellent truths.” The first and fundamental one is: “Pain is inseparable from existence.” This is the principle of all pessimism, ancient and modern. Schopenhauer, an out-and-out pessimist, lays down the allied maxim, “All pleasure is negative, that is, it consists in getting rid of a want or pain,”[13-1] a principle expressed before his time in the saying “the highest pleasure is the relief from pain.”
Consistently with this, Buddhism holds out as the ultimate of hope the state of Nirvana, in which existence is not, where the soul is “blown out” like the flame of a candle.
But physiology demolishes the corner-stone of this edifice when it shows that pain, so far from being inseparable from existence, has merely become, through transmitted experience, nearly inseparable from the progressive cessation of existence. While action and reaction are equal in inorganic nature, the principle of life modifies the operation of this universal law of force by bringing in nutrition, which, were it complete, would antagonize reaction. In such a case, pleasure would be continuous, pain null; action constant, reaction hypothetical. As, however, nutrition in fact never wholly and at once replaces the elements altered by vital action, both physicians and metaphysicians have observed that pleasure is the fore-runner of pain, and has the latter as its certain sequel.[14-1]
Physiologically and practically, the definition of pleasure is, maximum action with minimum waste.
This latter generalization is the explanation of the esthetic emotions. The modern theory of art rests not on a psychological but a physiological, and this in turn on a physical basis. Helmholtz’s theory of musical harmony depends on the experimental fact that a continued impression gives a pleasant, a discontinuous an unpleasant sensation. The mechanics of muscular structure prove that what are called graceful motions are those which are the mechanical resultant of the force of the muscle,—those which it can perform at least waste. The pleasure we take in curves, especially “the line of beauty,” is because our eyes can follow them with a minimum action of its muscles of attachment. The popular figure called the Grecian figure or the walls of Troy, is pleasant because each straight line is shorter, and at right angles to the preceding one, thus giving the greatest possible change of action to the muscles of the eye.