But it is already clear from the above facts that our human sense-activity is limited, not only in quantity, but in quality also. We can thus only perceive with our senses, especially with the eye and the sense of touch, a part of the qualities of the objects in our environment. And even this partial perception is incomplete, in the sense that our organs are imperfect, and our sensory nerves, acting as interpreters, communicate to the brain only a translation of the impressions received.
However, this acknowledged imperfection of our senses should not prevent us from recognizing their instruments, and especially the eye, to be organs of the highest type; together with the thought-organs in the brain, they are nature’s most valuable gift to man. Very truly does Albrecht Rau say: “All science is sensitive knowledge in the ultimate analysis; it does not deny, but interpret, the data of the senses. The senses are our first and best friends. Long before the mind is developed the senses tell man what he must do and avoid. He who makes a general disavowal of the senses in order to meet their dangers acts as thoughtlessly and as foolishly as the man who plucks out his eyes because they once fell on shameful things, or the man who cuts off his hand lest at any time it should reach out to the goods of his neighbor.” Hence Feuerbach is quite right in calling all philosophies, religions, and systems which oppose the principle of sense-action not only erroneous, but really pernicious. Without the senses there is no knowledge—“Nihil est in intellectu, quod non fuerit in sensu,” as Locke said. Twenty years ago I pointed out, in my chapter “On the Origin and Development of the Sense-Organs,”[32] the great service of Darwinism in giving us a profounder knowledge and a juster appreciation of the senses.
The thirst for knowledge of the educated mind is not contented with the defective acquaintance with the outer world which is obtained through our imperfect sense-organs. He endeavors to build up the sense-impressions which they have brought him into valuable knowledge. He transforms them into specific sense-perceptions in the sense-centres of the cortex of the brain, and combines them into presentations, by association, in the thought-centres. Finally, by a further concatenation of the groups of presentations he attains to connected knowledge. But this knowledge remains defective and unsatisfactory until the imagination supplements the inadequate power of combination of the intelligence, and, by the association of stored-up images, unites the isolated elements into a connected whole. Thus are produced new general presentative images, and these suffice to interpret the facts perceived and satisfy “reason’s feeling of causality.”
The presentations which fill up the gaps in our knowledge, or take its place, may be called, in a broad sense, “faith.” That is what happens continually in daily life. When we are not sure about a thing we say, I believe it. In this sense we are compelled to make use of faith even in science itself; we conjecture or assume that a certain relation exists between two phenomena, though we do not know it for certain. If it is a question of a cause, we form a hypothesis; though in science only such hypotheses are admitted as lie within the sphere of human cognizance, and do not contradict known facts. Such hypotheses are, for instance—in physics the theory of the vibratory movement of ether, in chemistry the hypothesis of atoms and their affinity, in biology the theory of the molecular structure of living protoplasm, and so forth.
The explanation of a great number of connected phenomena by the assumption of a common cause is called a theory. Both in theory and hypothesis “faith” (in the scientific sense) is indispensable; for here again it is the imagination that fills up the gaps left by the intelligence in our knowledge of the connection of things. A theory, therefore, must always be regarded only as an approximation to the truth; it must be understood that it may be replaced in time by another and better-grounded theory. But, in spite of this admitted uncertainty, theory is indispensable for all true science; it elucidates facts by postulating a cause for them. The man who renounces theory altogether, and seeks to construct a pure science with certain facts alone (as often happens with wrong-headed representatives of our “exact sciences”), must give up the hope of any knowledge of causes, and, consequently, of the satisfaction of reason’s demand for causality.
The theory of gravitation in astronomy (Newton), the nebular theory in cosmogony (Kant and Laplace), the principle of energy in physics (Meyer and Helmholtz), the atomic theory in chemistry (Dalton), the vibratory theory in optics (Huyghens), the cellular theory in histology (Schleiden and Schwann), and the theory of descent in biology (Lamarck and Darwin), are all important theories of the first rank; they explain a whole world of natural phenomena by the assumption of a common cause for all the several facts of their respective provinces, and by showing that all the phenomena thereof are inter-connected and controlled by laws which issue from this common cause. Yet the cause itself may remain obscure in character, or be merely a “provisional hypothesis.” The “force of gravity” in the theory of gravitation and in cosmogony, “energy” itself in its relation to matter, the “ether” of optics and electricity, the “atom” of the chemist, the living “protoplasm” of histology, the “heredity” of the evolutionist—these and similar conceptions of other great theories may be regarded by a sceptical philosophy as “mere hypotheses” and the outcome of scientific “faith,” yet they are indispensable for us, until they are replaced by better hypotheses.
The dogmas which are used for the explanation of phenomena in the various religions, and which go by the name of “faith” (in the narrower sense), are of a very different character from the forms of scientific faith we have enumerated. The two types, however—the “natural” faith of science and the “supernatural” faith of religion—are not infrequently confounded, so that we must point out their fundamental difference. Religious faith means always belief in a miracle, and as such is in hopeless contradiction with the natural faith of reason. In opposition to reason it postulates supernatural agencies, and, therefore, may be justly called superstition. The essential difference of this superstition from rational faith lies in the fact that it assumes supernatural forces and phenomena, which are unknown and inadmissible to science, and which are the outcome of illusion and fancy; moreover, superstition contradicts the well-known laws of nature, and is therefore irrational.
Owing to the great progress of ethnology during the century, we have learned a vast quantity of different kinds and practices of superstition, as they still survive in uncivilized races. When they are compared with each other and with the mythological notion of earlier ages, a manifold analogy is discovered, frequently a common origin, and eventually one simple source for them all. This is found in the “demand of causality in reason,” in the search for an explanation of obscure phenomena by the discovery of a cause. That applies particularly to such phenomena as threaten us with danger and excite fear, like thunder and lightning, earthquakes, eclipses, etc. The demand for a causal explanation of such phenomena is found in uncivilized races of the lowest grade, transmitted from their primate ancestors by heredity. It is even found in many other vertebrates. When a dog barks at the full moon, or at a ringing bell, of which it sees the hammer moving, or at a flag that flutters in the breeze, it expresses not only fear, but also the mysterious impulse to learn the cause of the obscure phenomenon. The crude beginnings of religion among primitive races spring partly from this hereditary superstition of their primate ancestors, and partly from the worship of ancestors, from various emotional impulses, and from habits which have become traditional.
The religious notions of modern civilized peoples, which they esteem so highly, profess to be on a much higher level than the “crude superstition” of the savage; we are told of the great advance which civilization has made in sweeping it aside. That is a great mistake. Impartial comparison and analysis show that they only differ in their special “form of faith” and the outer shell of their creed. In the clear light of reason the refined faith of the most liberal ecclesiastical religion—inasmuch as it contradicts the known and inviolable laws of nature—is no less irrational a superstition than the crude spirit-faith of primitive fetichism on which it looks down with proud disdain.
And if, from this impartial stand-point, we take a critical glance at the kinds of faith that prevail to-day in civilized countries, we find them everywhere saturated with traditional superstition. The Christian belief in Creation, the Trinity, the Immaculate Conception, the Redemption, the Resurrection and Ascension of Christ, and so forth, is just as purely imaginative as the belief in the various dogmas of the Mohammedan, Mosaic, Buddhistic, and Brahmanic religions, and is just as incapable of reconciliation with a rational knowledge of nature. Each of these religions is for the sincere believer an indisputable truth, and each regards the other as heresy and damnable error. The more confidently a particular sect considers itself “the only ark of salvation,” and the more ardently this conviction is cherished, the more zealously does it contend against all other sects and give rise to the fearful religious wars that form the saddest pages in the book of history. And all the time the unprejudiced “critique of pure reason” teaches us that all these different forms of faith are equally false and irrational, mere creatures of poetic fancy and uncritical tradition. Rational science must reject them all alike as the outcome of superstition.