"That every mental state has a nervous state for its immediate antecedent, though extremely probable, cannot hitherto be said to be proved, in the conclusive manner in which this can be proved of sensations; and even were it certain, yet every one must admit that we are wholly ignorant of the characteristics of these nervous states; we know not, and have no means of knowing, in what respect one of them differs from another.... The successions, therefore, which obtain among mental phenomena, do not admit of being deduced from the physiological laws of our nervous organization." "It must by no means be forgotten that the laws of mind may be derivative laws resulting from laws of animal life, and that their truth, therefore, may ultimately depend on physical conditions; and the influence of physiological states or physiological changes in altering or counter-acting the mental successions, is one of the most important departments of psychological study. But on the other hand, to reject the resource of psychological analysis, and construct the theory of mind solely on such data as physiology affords at present, seems to me as great[Pg 209] an error in principle, and an even more serious one in practice. Imperfect as is the science of mind, I do not scruple to affirm that it is in a considerably more advanced state than the portion of physiology which corresponds with it; and to discard the former for the latter appears to me to be an infringement of the true canons of inductive philosophy."
In a previous chapter[5] Mill had said:
"I am far from pretending that it may not be capable of proof, or that it is not an important addition to our knowledge, if proved, that certain motions in the particles of bodies are the conditions of the production of heat or light; that certain assignable physical modifications of the nerves may be the conditions, not only of our sensations and emotions, but even of our thoughts; that certain mechanical and chemical conditions may, in the order of nature, be sufficient to determine to action the physiological laws of life. All I insist upon, in common with every thinker who entertains any clear idea of the logic of science, is, that it shall not be supposed that by proving these things, one step would be made toward a real explanation of heat, light, or sensation; or that the generic peculiarity of those phenomena can be in the least degree evaded by any such discoveries, however well established. Let it be shown, for instance, that the most complex series of physical causes and effects succeed one another in the eye and in the brain, to produce a sense of color; rays falling on the eye, refracted, converging, crossing one another, making an inverted image on the retina; and after this a motion—let it be a vibration, or a rush of nervous fluid, or whatever else you are pleased to suppose, along the optic nerve—a propagation of this motion to the brain itself, and as many more different motions as you choose;[Pg 210] still, at the end of these motions there is something which is not motion, there is a feeling or sensation of color. The mode in which any one of the motions produces the next, may possibly be susceptible of explanation by some general law of motion; but the mode in which the last motion produces the sensation of color cannot be explained by any motion; it is the law of color, which is, and must always remain a peculiar thing. Where our consciousness recognizes between two phenomena an inherent distinction; where we are sensible of a difference, which is not merely of degree; and feel that no adding one of the phenomena to itself will produce the other; any theory which attempts to bring either under the laws of the other must be false."
To precisely the same effect, DuBois Reymond, in an address to the Congress of German Naturalists given in Leipsic:
"It is absolutely and forever inconceivable that a number of carbon, hydrogen, nitrogen and oxygen atoms, should be otherwise than indifferent to their own position and motion, past, present, or future. It is utterly inconceivable how consciousness should result from their joint action."
The position of John Tyndall is well understood. It was avowed in 1860 in the Saturday Review; again in his address to the Mathematical and Physical Section of the British Association in 1868, wherein he declared that
"The passage from the physics of the brain to the corresponding facts of consciousness is unthinkable. Granted that[Pg 211] a thought and a definite molecular action in the brain occur simultaneously, we do not possess the organ, nor, apparently, any rudiment of the organ, which would enable us to pass by a process of reasoning from the one phenomenon to the other. They appear together, but we do not know why."
In 1875, reviewing Martineau in the Popular Science Monthly for December, Tyndall calls attention to these declarations, and quotes other language of his own to the same purpose:
"You cannot satisfy the understanding in its demand for logical continuity between molecular processes and the phenomena of consciousness. This is a rock on which materialism must inevitably split whenever it pretends to be a complete philosophy of the human mind."
Mr. John Fiske, a disciple of Herbert Spencer, and an exceedingly able expositor of the philosophy of which Spencer is the acknowledged chief, makes assertions equally positive:[6]