- 107. In the Cartesian system the cause of motion was pressure within a plenum. But in the seventeenth century this notion encountered the system of Newton, a system which seemed to involve action at a distance.

In the year 1728 Voltaire wrote from London:

"When a Frenchman arrives in London, he finds a very great change, in philosophy as well as in most other things. In Paris he left the world all full of matter; here he finds absolute vacua. At Paris the universe is seen filled up with ethereal vortices, while here the same s.p.a.ce is occupied with the play of the invisible forces of gravitation. In Paris the earth is painted for us longish like an egg, and in London it is oblate like a melon. At Paris the pressure of the moon causes the ebb and flow of tides; in England, on the other hand, the sea gravitates toward the moon, so that at the same time when the Parisians demand high water of the moon, the gentlemen of London require an ebb."[232:6]

But these differences are not matters of taste, nor even rival hypotheses upon an equal footing. The Newtonian system of mechanics, the consummation of a development initiated by Galileo, differed from the vortex theory of Descartes as exact science differs from speculation and unverified conjecture. And this difference of method carried with it eventually certain profound differences of content, distinguishing the Newtonian theory even from that of Democritus, with which it had so much in common. Although Democritus had sought to avoid the element of purposiveness in the older hylozoism by referring the motions of bodies as far as possible to the impact of other bodies, he nevertheless attributed these motions ultimately to _weight_, signifying thereby a certain _downward disposition_. Now it is true that in his general belief Newton himself is not free from hylozoism. He thought of the motions of the planets themselves as initiated and quickened by a power emanating ultimately from G.o.d. They are "impressed by an intelligent Agent," and

"can be the effect of nothing else than the wisdom and skill of a powerful ever-living Agent who, being in all places, is more able by his will to move the bodies within his boundless uniform _sensorium_, and thereby to form and reform the parts of the universe, than we are by our will to move the parts of our own bodies."[233:7]

But by the side of these statements must be set his famous disclaimer, "_hypotheses non fingo_." In his capacity of natural philosopher he did not seek to explain motions, but only to describe them. Disbelieving as he did in action at a distance, he saw no possibility of explanation short of a reference of them to G.o.d; but such "hypotheses" he thought to be no proper concern of science. As a consequence, the mathematical formulation of motions came, through him, to be regarded as the entire content of mechanics. The notion of an efficient cause of motion is still suggested by the term _force_, but even this term within the system of mechanics refers always to a definite amount of motion, or measurement of relative motion. And the same is true of _attraction_, _action_, _reaction_, and the like. The further explanation of motion, the definition of a virtue or potency that produces it, first a neglected problem, then an irrelevant problem, is finally, for a naturalistic philosophy in which this progression is completed, an insoluble problem. For the sequel to this purely descriptive procedure on the part of science is the disavowal of "metaphysics" by those who will have no philosophy but science. Thus the scientific conservatism of Newton has led to the positivistic and agnostic phase of naturalism. But a further treatment of this development must be reserved until the issue of epistemology shall have been definitely raised.

A different emphasis within the general mechanical scheme, attaching especial importance to the conceptions of force and energy, has led to a rival tendency in science and a contrasting type of naturalism. The mechanical hypotheses. .h.i.therto described are all of a simple and readily depicted type. They suggest an imagery quite in accord with common-sense and with observation of the motions of great ma.s.ses like the planets.

Material particles are conceived to move within a containing s.p.a.ce; the motions of corpuscles, atoms, or the minute parts of ether, differing only in degree from those of visible bodies. The whole physical universe may be represented in the imagination as an aggregate of bodies partic.i.p.ating in motions of extraordinary complexity, but of one type.

But now let the emphasis be placed upon the determining causes rather than upon the moving bodies themselves. In other words, let the bodies be regarded as attributive and the forces as substantive. The result is a radical alteration of the mechanical scheme and the transcendence of common-sense imagery. This was one direction of outgrowth from the work of Newton. His force of gravitation prevailed between bodies separated by s.p.a.ces of great magnitude. Certain of the followers of Newton, notably Cotes, accepting the formulas of the master but neglecting his allusions to the agency of G.o.d, accepted the principle of action at a distance. _Force_, in short, _was conceived to pervade s.p.a.ce of itself_.

But if force be granted this substantial and self-dependent character, what further need is there of matter as a separate form of ent.i.ty? For does not the presence of matter consist essentially in resistance, itself a case of force? Such reflections as these led Boscovich and others to the radical departure of defining material particles _as centres of force_.

[Sidenote: The Development and Extension of the Conception of Energy.]

- 108. But a more fruitful hypothesis of the same general order is due to the attention directed to the conception of _energy_, or capacity for work, by experimental discoveries of the possibility of reciprocal transformations without loss, of motion, heat, electricity, and other processes. The principle of the conservation of energy affirms the quant.i.tative constancy of that which is so transformed, measured, for example, in terms of capacity to move units of ma.s.s against gravity. The exponents of what is called "energetics" have in many cases come to regard that the quant.i.ty of which is so conserved, as a substantial reality whose forms and distributions compose nature. A contemporary scientist, whose synthetic and dogmatic habit of mind has made him eminent in the ranks of popular philosophy, writes as follows:

"Mechanical and chemical energy, sound and heat, light and electricity, are mutually convertible; they seem to be but different modes of one and the same fundamental force or _energy_. Thence follows the important thesis of the unity of all natural forces, or, as it may also be expressed, the 'monism of energy.'"[236:8]

The conception of energy seems, indeed, to afford an exceptional opportunity to naturalism. We have seen that the matter-motion theory was satisfied to ignore, or regard as insoluble, problems concerning the ultimate causes of things. Furthermore, as we shall presently see to better advantage, the more strictly materialistic type of naturalism must regard thought as an anomaly, and has no little difficulty with life. But the conception of energy is more adaptable, and hence better qualified to serve as a common denominator for various aspects of experience. The very readiness with which we can picture the corpuscular scheme is a source of embarra.s.sment to the seeker after unity. That which is so distinct is bristling with incompatibilities. The most aggressive materialist hesitates to describe thought as a motion of bodies in s.p.a.ce. Energy, on the other hand, exacts little if anything beyond the character of measurable power. Thought is at any rate in some sense a power, and to some degree measurable. Recent discoveries of the dependence of capacity for mental exertion upon physical vitality and measurements of chemical energy received into the system as food, and somehow exhausted by the activities of thought, have lent plausibility to the hypothesis of a universal energy of which physical and "psychical" processes are alike manifestations. And the conception of energy seems capable not only of unifying nature, but also of satisfying the metaphysical demand for an efficient and moving cause. This term, like "force" and "power," is endowed with such a significance by common sense. Indeed, naturalism would seem here to have swung round toward its hylozoistic starting-point. The exponent of energetics, like the naive animistic thinker, attributes to nature a power like that which he feels welling up within himself. When he acts upon the environment, like meets like. Energetics, it is true, may obtain a definite meaning for its central conception from the measurable behavior of external bodies, and a meaning that may be quite free from vitalism or teleology. But in his extension of the conception the author of a philosophical energetics abandons this strict meaning, and blends his thought even with a phase of subjectivism, known as _panpsychism_.[238:9] This theory regards the inward life of all nature as h.o.m.ogeneous with an immediately felt activity or appetency, as energetics finds the inner life to be h.o.m.ogeneous with the forces of nature. Both owe their philosophical appeal to their apparent success in unifying the world upon a direct empirical basis, and to their provision for the practical sense of reality.

Such, in brief, are the main alternatives available for a naturalistic theory of being, in consequence of the historical development of the fundamental conceptions of natural science.

[Sidenote: The Claims of Naturalism.]

- 109. We turn now to an examination of the manner in which naturalism, equipped with working principles, seeks to meet the special requirements of philosophy. The conception of the unity of nature is directly in the line of a purely scientific development, but naturalism takes the bold and radical step of regarding nature so unified as coextensive with the real, or at any rate knowable, universe. It will be remembered that among the early Greeks Anaxagoras had referred the creative and formative processes of nature to a non-natural or rational agency, which he called the _Nous_. The advent.i.tious character of this principle, the external and almost purely nominal part which it played in the actual cosmology of Anaxagoras, betrayed it into the hands of the atomists, with their more consistently naturalistic creed. Better, these maintain, the somewhat dogmatic extension of conceptions proved to be successful in the description of nature, than a vague dualism which can serve only to distract the scientific attention and people the world with obscurities. There is a remarkable pa.s.sage in Lucretius in which atomism is thus written large and inspired with cosmical eloquence:

"For verily not by design did the first-beginnings of things station themselves each in its right place guided by keen intelligence, nor did they bargain sooth to say what motions each should a.s.sume, but because many in number and shifting about in many ways throughout the universe, they are driven and tormented by blows during infinite time past, after trying motions and unions of every kind at length they fall into arrangements such as those out of which our sum of things has been formed, and by which too it is preserved through many great years, when once it has been thrown into the appropriate motions, and causes the streams to replenish the greedy sea with copious river waters, and the earth, fostered by the heat of the sun, to renew its produce, and the race of living things to come up and flourish, and the gliding fires of ether to live: all which these several things could in no wise bring to pa.s.s, unless a store of matter could rise up from infinite s.p.a.ce, out of which store they are wont to make up in due season whatever has been lost."[240:10]

The prophecy of La Place, the great French mathematician, voices the similar faith of the eighteenth century in a mechanical understanding of the universe:

"The human mind, in the perfection it has been able to give to astronomy, affords a feeble outline of such an intelligence.

Its discoveries in mechanics and in geometry, joined to that of universal gravitation, have brought it within reach of comprehending in the same a.n.a.lytical expressions the past and future states of the system of the world."[241:11]

As for G.o.d, the creative and presiding intelligence, La Place had "no need of any such hypothesis."

[Sidenote: The Task of Naturalism.]

- 110. But these are the boasts of Homeric heroes before going into battle. The moment such a general position is a.s.sumed there arise sundry difficulties in the application of naturalistic principles to special interests and groups of facts. It is one thing to project a mechanical scheme in the large, but quite another to make explicit provision within it for the origin of nature, for life, for the human self with its ideals, and for society with its inst.i.tutions. The naturalistic method of meeting these problems involves a reduction all along the line in the direction of such categories as are derived from the infra-organic world. That which is not like the planetary system must be construed as mechanical by indirection and subtlety.

[Sidenote: The Origin of the Cosmos.]

- 111. The origin of the present known natural world was the first philosophical question to be definitely met by science. The general form of solution which naturalism offers is antic.i.p.ated in the most ancient theories of nature. These already suppose that the observed mechanical processes of the circular or periodic type, like the revolutions and rotations of the stars, are incidents in a historical mechanical process of a larger scale. Prior to the present fixed motions of the celestial bodies, the whole ma.s.s of cosmic matter partic.i.p.ated in irregular motions a.n.a.logous to present terrestrial redistributions. Such motions may be understood to have resulted in the integration of separate bodies, to which they at the same time imparted a rotary motion. It is such a hypothesis that Lucretius paints in his bold, impressionistic colors.

But the development of mechanics paved the way for a definite scientific theory, the so-called "nebular hypothesis," announced by La Place in 1796, and by the philosopher Kant at a still earlier date. Largely through the Newtonian principle of the parallelogram of forces, the present ma.s.ses, orbits, and velocities were a.n.a.lyzed into a more primitive process of concentration within a nebulous or highly diffused aggregate of matter. And with the aid of the principle of the conservation of energy this theory appears to make possible the derivation of heat, light, and other apparently non-mechanical processes from the same original energy of motion.

But a persistently philosophical mind at once raises the question of the origin of this primeval nebula itself, with a definite organization and a vast potential energy that must, after all, be regarded as a part of nature rather than its source. Several courses are here open to naturalism. It may maintain that the question of ultimate origin is unanswerable; it may regard such a process of concentration as extending back through an infinitely long past;[243:12] or, and this is the favorite alternative for more constructive minds, the historical cosmical process may be included within a still higher type of periodic process, which is regarded as eternal. This last course has been followed in the well-known synthetic naturalism of Herbert Spencer.

"Evolution," he says, "is the progressive integration of matter and dissipation of motion." But such a process eventually runs down, and may be conceived as giving place to a counter-process of devolution which scatters the parts of matter and gathers another store of potential motion. The two processes in alternation will then const.i.tute a cosmical system without beginning or end.

In such wise a sweeping survey of the physical universe may be thought in the terms of natural science. The uniformitarian method in geology, resolving the history of the crust of the earth into known processes, such as erosion and igneous fusion;[244:13] and spectral a.n.a.lysis, with its discoveries concerning the chemical const.i.tuents of distant bodies through the study of their light, have powerfully reenforced this effort of thought, and apparently completed an outline sketch of the universe in terms of infra-organic processes.

[Sidenote: Life. Natural Selection.]

- 112. But the cosmos must be made internally h.o.m.ogeneous in these same terms. There awaits solution, in the first place, the serious problem of the genesis and maintenance of life within a nature that is originally and ultimately inorganic. The a.s.similation of the field of biology and physiology to the mechanical cosmos had made little real progress prior to the nineteenth century. Mechanical theories had, indeed, been projected in the earliest age of philosophy, and proposed anew in the seventeenth century.[245:14] Nevertheless, the structural and functional teleology of the organism remained as apparently irrefutable testimony to the inworking of some principle other than that of mechanical necessity. Indeed, the only fruitful method applicable to organic phenomena was that which explained them in terms of purposive adaptation. And it was its provision for a mechanical interpretation of this very principle that gave to the Darwinian _law of natural selection_, promulgated in 1859 in the "Origin of Species," so profound a significance for naturalism. It threatened to reduce the last stronghold of teleology, and completely to dispense with the intelligent Author of nature.

Darwin's hypothesis sought to explain the origin of animal species by survival under compet.i.tive conditions of existence through the possession of a structure suited to the environment. Only the most elementary organism need be presupposed, together with slight variations in the course of subsequent generations, and both may be conceived to arise mechanically. There will then result in surviving organisms a gradual acc.u.mulation of such variations as promote survival under the special conditions of the environment. Such a principle had been suggested as early as the time of Empedocles, but it remained for Darwin to establish it with an unanswerable array of observation and experimentation. If any organism whatsoever endowed with the power of generation be allowed to have somehow come to be, naturalism now promises to account for the whole subsequent history of organic phenomena and the origin of any known species.

[Sidenote: Mechanical Physiology.]

- 113. But what of life itself? The question of the derivation of organic from inorganic matter has proved insoluble by direct means, and the case of naturalism must here rest upon such facts as the chemical h.o.m.ogeneity of these two kinds of matter, and the conformity of physiological processes to more general physical laws. Organic matter differs from inorganic only through the presence of proteid, a peculiar product of known elements, which cannot be artificially produced, but which is by natural means perpetually dissolved into these elements without any discoverable residuum. Respiration may be studied as a case of aerodynamics, the circulation of the blood as a case of hydrodynamics, and the heat given off in the course of work done by the body as a case of thermodynamics. And although vitalistic theories still retain a place in physiology, as do teleological theories in biology, on the whole the naturalistic programme of a reduction of organic processes to the type of the inorganic tends to prevail.

[Sidenote: Mind. The Reduction to Sensation.]

- 114. The history of naturalism shows that, as in the case of life, so also in the case of _mind_, its hypotheses were projected by the Greeks, but precisely formulated and verified only in the modern period of science. In the philosophy of Democritus the soul was itself an atom, finer, rounder, and smoother than the ordinary, but thoroughly a part of the mechanism of nature. The processes of the soul are construed as interactions between the soul and surrounding objects. In sensation, the thing perceived produces images by means of effluxes which impinge upon the soul-atom. These images are not true reports of the outer world, but must be revised by thought before its real atomic structure emerges.

For this higher critical exercise of thought Democritus devised no special atomic genesis. The result may be expressed either as the invalidity of such operations of mind as he could provide for in his universe, or the irreducibility to his chosen first principles of the very thought which defined them. Later naturalism has generally sacrificed epistemology to cosmology, and reduced thought to sensation.

Similarly, will has been regarded as a highly developed case of instinct. Knowledge and will, construed as sensation and instinct, may thus be interpreted in the naturalistic manner within the field of biology.

[Sidenote: Automatism.]

- 115. But the actual content of sensation, and the actual feelings which attend upon the promptings of instinct, still stubbornly testify to the presence in the universe of something belonging to a wholly different category from matter and motion. The att.i.tude of naturalism in this crucial issue has never been fixed and unwavering, but there has gradually come to predominate a method of denying to the inner life all efficacy and real significance in the cosmos, while admitting its presence on the scene. It is a strange fact of history that Descartes, the French philosopher who prided himself on having rid the soul of all dependence on nature, should have greatly contributed to this method.

But it is perhaps not so strange when we consider that every dualism is, after all, symmetrical, and that consequently whatever rids the soul of nature at the same time rids nature of the soul. It was Descartes who first conceived the body and soul to be utterly distinct substances. The corollary to this doctrine was his _automatism_, applied in his own system to animals other than man, but which those less concerned with religious tradition and less firmly convinced of the soul's originating activity were not slow to apply universally. This theory conceived the vital processes to take place quite regardless of any inner consciousness, or even without its attendance. To this radical theory the French materialists of the eighteenth century were especially attracted. With them the active soul of Descartes, the distinct spiritual ent.i.ty, disappeared. This latter author had himself admitted a department of the self, which he called the "pa.s.sions," in which the course and content of mind is determined by bodily conditions. Extending this conception to the whole province of mind, they employed it to demonstrate the thorough-going subordination of mind to body. La Mettrie, a physician and the author of a book ent.i.tled "L'Homme Machine," was first interested in this thesis by a fever delirium, and afterward adduced anatomical and pathological data in support of it. The angle from which he views human life is well ill.u.s.trated in the following:

"What would have sufficed in the case of Julius Caesar, of Seneca, of Petronius, to turn their fearlessness into timidity or braggartry? An obstruction in the spleen, the liver, or the _vena portae_. For the imagination is intimately connected with these viscera, and from them arise all the curious phenomena of hypochondria and hysteria. . . . 'A mere nothing, a little fibre, some trifling thing that the most subtle anatomy cannot discover, would have made two idiots out of Erasmus and Fontenelle.'"[250:15]

[Sidenote: Radical Materialism. Mind as an Epiphenomenon.]

- 116. The extreme claim that the soul is a physical organ of the body, identical with the brain, marked the culmination of this militant materialism, so good an instance of that over-simplification and whole-hearted conviction characteristic of the doctrinaire propagandism of France. Locke, the Englishman, had admitted that possibly the substance which thinks is corporeal. In the letters of Voltaire this thought has already found a more positive expression:

"I am body, and I think; more I do not know. Shall I then attribute to an unknown cause what I can so easily attribute to the only fruitful cause I am acquainted with? In fact, where is the man who, without an absurd G.o.dlessness, dare a.s.sert that it is impossible for the Creator to endow matter with thought and feeling?"[251:16]

Finally, Holbach, the great systematizer of this movement, takes the affair out of the hands of the Creator and definitively announces that "a sensitive soul is nothing but a human brain so const.i.tuted that it easily receives the motions communicated to it."[251:17]

This theory has been considerably tempered since the age of Holbach.

Naturalism has latterly been less interested in identifying the soul with the body, and more interested in demonstrating its dependence upon specific bodily conditions, after the manner of La Mettrie. The so-called higher faculties, such as thought and will, have been related to central or _cortical_ processes of the nervous system, processes of connection and complication which within the brain itself supplement the impulses and sensations congenitally and externally stimulated. The term "epiphenomenon" has been adopted to express the distinctness but entire dependence of the mind. Man is "a conscious automaton." The real course of nature pa.s.ses through his nervous system, while consciousness attends upon its functions like a shadow, present but not efficient.[252:18]

[Sidenote: Knowledge, Positivism and Agnosticism.]

- 117. Holbach's "Systeme de la Nature," published in 1770, marks the culmination of the unequivocally materialistic form of naturalism. Its epistemological difficulties, always more or less in evidence, have since that day sufficed to discredit materialism, and to foster the growth of a critical and apologetic form of naturalism known as _positivism_ or _agnosticism_. The modesty of this doctrine does not, it is true, strike very deep. For, although it disclaims knowledge of ultimate reality, it also forbids anyone else to have any. Knowledge, it affirms, can be of but one type, that which comprises the verifiable laws governing nature. All questions concerning first causes are futile, a stimulus only to excursions of fancy popularly mistaken for knowledge. The superior certainty and stability which attaches to natural science is to be permanently secured by the savant's steadfast refusal to be led away after the false G.o.ds of metaphysics.

But though this is sufficient ground for an agnostic policy, it does prove an agnostic theory. The latter has sprung from a closer a.n.a.lysis of knowledge, though it fails to make a very brave showing for thoroughness and consistency. The crucial point has already been brought within our view. The general principles of naturalism require that knowledge shall be reduced to sensations, or impressions of the environment upon the organism. But the environment and the sensations do not correspond. The environment is matter and motion, force and energy; the sensations are of motions, to be sure, but much more conspicuously of colors, sounds, odors, pleasures, and pains. Critically, this may be expressed by saying that since the larger part of sense-perception is so unmistakably subjective, and since all knowledge alike must be derived from this source, knowledge as a whole must be regarded as dealing only with appearances. There are at least three agnostic methods progressing from this point. All agree that the inner or essential reality is unfathomable. But, in the first place, those most close to the tradition of materialism maintain that the most significant appearances, the primary qualities, are those which compose a purely quant.i.tative and corporeal world. The inner essence of things may at any rate be _approached_ by a monism of matter or of energy. This theory is epistemological only to the extent of moderating its claims in the hope of lessening its responsibility. Another agnosticism places all sense qualities on a par, but would regard physics and psychology as complementary reports upon the two distinct series of phenomena in which the underlying reality expresses itself. This theory is epistemological to the extent of granting knowledge, viewed as perception, as good a standing in the universe as that which is accorded to its object. But such a dualism tends almost irresistibly to relapse into materialistic monism, because of the fundamental place of physical conceptions in the system of the sciences. Finally, in another and a more radical phase of agnosticism, we find an attempt to make full provision for the legitimate problems of epistemology. The only datum, the only existent accessible to knowledge, is said to be the sensation, or state of consciousness. In the words of Huxley:

"What, after all, do we know of this terrible 'matter' except as a name for the unknown and hypothetical cause of states of our own consciousness? And what do we know of that 'spirit'

over whose threatened extinction by matter a great lamentation is arising, . . . except that it is also a name for an unknown and hypothetical cause, or condition, of states of consciousness?"[255:19]

The physical world is now to be regarded as a construction which does not a.s.similate to itself the content of sensations, but enables one to antic.i.p.ate them. The sensation signifies a contact to which science can provide a key for practical guidance.

[Sidenote: Experimentalism.]