Front Page Titles (by Subject) CHAPTER II.: CONNEXION OF MIND AND LIFE. - The Principles of Psychology
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CHAPTER II.: CONNEXION OF MIND AND LIFE. - Herbert Spencer, The Principles of Psychology 
The Principles of Psychology (London: Longman, Brown, Green and Longmans, 1855).
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CONNEXION OF MIND AND LIFE.
§ 111. The only phenomena to which those of intelligence are allied, are the phenomena of vital activity in its lower forms; and to these their alliance is close. Though we commonly regard mental and bodily life as distinct, it needs only to ascend somewhat above the ordinary point of view, to see that they are but sub-divisions of life in general; and that no line of demarcation can be drawn between them, otherwise than arbitrarily. Doubtless, to those who persist, after the popular fashion, in contemplating only the extreme forms of the two, this assertion will appear as incredible as the assertion that a tree arises by imperceptible changes out of a seed, would appear to one who had seen none of the intermediate stages. But in the absence of prejudice, an examination of the successive links, will produce conviction in the one case as in the other. It is not more certain that from the simple reflex action by which the infant sucks, up to the elaborate reasonings of the adult man, the progress is by daily infinitesimal steps, than it is certain that between the automatic actions of the lowest creatures, and the highest conscious actions of the human race, a series of actions, displayed by the various tribes of the animal kingdom, may be so placed, as to render it impossible to say of any one step in the series—Here intelligence begins. If, from the advanced man of science, pursuing his inquiries with a full understanding of the ratiocinative and inductive processes he employs, we descend to the man of ordinary education, who reasons well and comprehensively, but without knowing how; if, going a grade lower, we analyze the thinkings of the villager, whose highest generalizations are but little wider than those which local events afford data for; if, again, we sink to the inferior human races, who cannot be induced to think, who cannot take in ideas of any complexity, and whose conceptions of number scarcely transcend those of the dog;∗ if we take next the higher quadrumana, hosts of whose actions are quite as rational as those of school-boys, and whose language, however unintelligible to us, is manifestly more or less intelligible to each other; if, from these, we proceed to domesticated animals, whose power of reasoning is conceded even by those under theological bias,† with the qualification that it is special and not general—a qualification which equally holds between the different grades of human reasoning; if, from the most sagacious quadrupeds, we descend to the less and less sagacious ones, noting as we pass how gradual is the transition to those which exhibit no power of modifying their actions to suit special conditions, and which so prove themselves to be guided by what we call instinct; if, from observing the operation of the higher instincts, in which a complicated combination of motions is produced by a complicated combination of stimuli, we go down to the successively lower ones, in which the applied stimuli and the resulting motions are less and less complex; if, presently, we find ourselves merging into what is technically known as reflex action, in which a single motion follows a single stimulus; if, from the creatures in which this implies the irritation of a nerve and the contraction of a muscle, we descend yet lower, to creatures devoid of nervous and muscular systems, and discover that in these the irritability and the contractility are exhibited by the same tissue, which tissue also fulfils the functions of assimilation, secretion, respiration, and reproduction; and if, finally, we perceive that each of the phases of intelligence here instanced, shades off into the adjacent ones by modifications too numerous to specify, too minute to describe, we shall in some measure realize the fact, that no definite separation can be effected between the phenomena of mind and those of vitality in general. Without here, however, urging anything further in support of this position, and without requiring that it shall be admitted, present purposes will be sufficiently served by a recognition of the unquestionable truth, that there is a close relationship between the actions we call mental and the actions we call organic—that these classes of actions are more nearly allied to each other than to any remaining classes.
§ 112. Bodily and mental life being thus divisions of life in general—being related to each other as species of which life in general is the genus—it results from the conclusion reached in the last chapter, that we shall most readily find a true generalization of mental phenomena, by comparing them with the lower vital phenomena, and inquiring what characteristic the two classes have in common. The propriety of this course may be recognized even in the absence of any considerations touching method. Only in some formula which includes all manifestations of intelligence, without exception, can we have a safe and sufficient foundation for a Synthetic Psychology. And saying nothing of the inseparableness of the two orders of vital action, it requires but to consider that the process of making a successful astronomical prediction, differs as widely from that by which the distance of an adjacent body is recognized or the hand moved towards it, as this does from the simple reflex stimulation of a gland—it requires only to consider this, to see that a formula including all manifestations of intelligence, must be one which also includes organic actions. Organic actions, however, and the actions which we class as intelligent, comprehend when taken together all the phenomena of vitality. Hence, then, it follows, that in seeking out a characteristic common to both, we are in fact seeking out the characteristic of vital actions in general—the characteristic by which they are distinguished from non-vital actions. Our point of departure must be an inquiry after that peculiarity displayed alike by all the processes of life.
§ 113. Before proceeding to this inquiry, it may be well to remark, that any conclusion to which it may lead, must be expected to have very little apparent bearing upon our special topic. The more general is any truth, the more vague it is. The greater the range and the more diverse the character of the phenomena, the less apparent relation will a proposition which is true of them all, have to each. Little connection is visible between the axiom—“Things that are equal to the same thing are equal to one another,” and the theorems of Euclid. The law that portions of matter attract each other with a force varying inversely as the square of the distance, does not seem to offer any explanation of the perturbations of Uranus, or the rising of a balloon. Similarly, we may be sure, à priori, that a fact predicable equally of all the infinitely varied actions going on in living bodies, must give little obvious promise of explaining the phenomena classed under the title of Psychology; and especially those highly complex phenomena of human intelligence, with which, in the minds of most, that title is associated.
[∗]See Galton's account of the Damaras.
[†]Dr. Whately for example.