The aim and effort of science is to explain the unknown in terms of the known. Explanation, therefore, is conditioned by knowledge. You have probably heard the story of the German peasant, who, in early railway days, was taken to see the performance of a locomotive. He had never known carriages to be moved except by animal power. Every explanation outside of this conception lay beyond his experience, and could not be invoked. After long reflection therefore, and seeing no possible escape from the conclusion, he exclaimed confidently to his companion, 'Es muessen doch Pferde darin sein ' — There must be horses inside. Amusing as this locomotive theory may seem, it illustrates a deep-lying truth.
With reference to our present question, some may be disposed to press upon me such considerations as these :— Your motor nerves are so many speaking-tubes, through which messages are sent from the man to the world; and your sensor nerves are so many conduits through which the whispers of the world are sent back to the man. But you have not told us where is the man. Who or what is it that sends and receives those messages through the bodily organism? Do not the phenomena point to the existence of a self within the self, which acts through the body as through a skilfully constructed instrument? You picture the muscles as hearkening to the commands sent through the motor nerves, and you picture the sensor nerves as the vehicles of incoming intelligence; are you not bound to supplement this mechanism by the assumption of an entity which uses it? In other words, are you not forced by Tour own exposition into the hypothesis of a free human soul?
This is fair reasoning now, and at a certain stage of the world's knowledge, it might well have been deemed conclusive. Adequate reflection, however, shows that instead of introducing light into our minds, this hypothesis considered scientifically increases our darkness. You do not in this case explain the unknown in terms of the known, which, as stated above, is the method of science, but you explain the unknown in terms of the more unknown. Try to mentally visualise this soul as an entity distinct from the body, and the difficulty immediately appears. From the side of science all that we are warranted in stating is that the terror, hope, sensation, and calculation of Lange's merchant, are psychical phenomena produced by, or associated with, the molecular processes set up by waves of light in a previously prepared brain.
When facts present themselves let us dare to face them, but let the man of science equally dare to confess ignorance where it prevails. What then is the causal connection, if any, between the objective and subjective — between molecular motions and states of consciousness? My answer is: I do not see the connection, nor have I as yet met anybody who does.
It is no explanation to say that the objective and subjective effects are two sides of one and the same phenomenon. Why should the phenomenon have two sides? This is the very core of the difficulty. There are plenty of molecular motions which do not exhibit this two-sidedness. Does water think or feel when it runs into frost-ferns upon a window-pane? If not, why should the molecular motion of the brain be yoked to this mysterious companion — consciousness? We can form a coherent picture of the physical processes — the stirring of the brain, the thrilling of the nerves, the discharging of the muscles, and all the subsequent mechanical motions of the organism. But we can present to our minds no picture of the process whereby consciousness emerges, either as a necessary link or as an accidental by-product of this series of actions. Yet it certainly does emerge — the prick of a pin suffices to prove that molecular motion can produce consciousness. The reverse process of the production of motion by consciousness is equally unpresentable to the mind. We are here, in fact, upon the boundary line of the intellect, where the ordinary canons of science fail to extricate us from our difficulties. If we are true to these canons, we must deny to subjective phenomena all influence on physical processes. Observation proves that they interact, but in passing from one to the other, we meet a blank which mechanical deduction is unable to fill. Frankly stated, we have here to deal with facts almost as difficult to seize mentally as the idea of a soul. And if you are content to make your 'soul' a poetic rendering of a phenomenon which refuses the yoke of ordinary physical laws, I, for one, would not object to this exercise of ideality. Amid all our speculative uncertainty, however, there is one practical point as clear as the day; namely, that the brightness and the usefulness of life, as well as its darkness and disaster, depend to a great extent upon our own use or abuse of this miraculous organ.
Accustomed as I am to harsh language, I am quite prepared to hear my 'poetic rendering' branded as a 'falsehood' and a 'fib.' The vituperation is unmerited, for poetry or ideality, and untruth are assuredly very different things. The one may vivify, while the other, kills. When St. John extends the notion of a soul to 'souls washed in the blood of Christ' does he 'fib'? Indeed, if the appeal to ideality is censurable, Christ himself ought not to have escaped censure. Nor did he escape it. 'How can this man give us his flesh to eat?' expressed the sceptical flouting of unpoetic natures. Such are still amongst us. Cardinal Manning would doubtless tell any Protestant who rejects the doctrine of transubstantiation that he 'fibs' away the plain words of his Saviour when he reduces 'the Body of the Lord' in the sacrament to a mere figure of speech.
Though misuse may render it grotesque or insincere, the idealisation of ancient conceptions, when done consciously and above board, has, in my opinion, an important future. We are not radically different from our historic ancestors, and any feeling which affected them profoundly, requires only appropriate clothing to affect us. The world will not lightly relinquish its heritage of poetic feeling, and metaphysic will be welcomed when it abandons its pretensions to scientific discovery and consents to be ranked as a kind of poetry. 'A good symbol,' says Emerson, 'is a missionary to persuade thousands. The Vedas, the Edda, the Koran, are each remembered by its happiest figure. There is no more welcome gift to men than a new symbol. They assimilate themselves to it, deal with it in all ways, and it will last a hundred years. Then comes a new genius and brings another.' Our ideas of God and the soul are obviously subject to this symbolic mutation. They are not now what they were a century ago. They will not be a century hence what they are now. Such ideas constitute a kind of central energy in the human mind, capable, like the energy of the physical universe, of assuming various shapes and undergoing various transformations. They baffle and elude the theological mechanic who would carve them to dogmatic forms. They offer themselves freely to the poet who understands his vocation, and whose function is, or ought to be, to find 'local habitation' for thoughts woven into our subjective life, but which refuse to be mechanically defined.
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We now stand face to face with the final problem. It is this: Are the brain, and the moral and intellectual processes known to be associated with the brain — and, as far as our experience goes, indissolubly associated — subject to the laws which we find paramount in physical nature? Is the will of man, in other words, free, or are it and nature equally 'bound fast in fate'? From this latter conclusion, after he had established it to the entire satisfaction of his understanding, the great German thinker Fichte recoiled. You will find the record of this struggle between head and heart in his book, entitled 'Die Bestimmung des Menschen' — The Vocation of Man. [Footnote: Translated by Dr. William Smith of Edinburgh; Truebner, 1873.] Fichte was determined at all hazards to maintain his freedom, but the price he paid for it indicates the difficulty of the task. To escape from the iron necessity seen everywhere reigning in physical nature, he turned defiantly round upon nature and law, and affirmed both of them to be the products of his own mind. He was not going to be the slave of a thing which he had himself created. There is a good deal to be said in favour of this view, but few of us probably would be able to bring into play the solvent transcendentalism whereby Fichte melted his chains.
Why do some regard this notion of necessity with terror, while others do not fear it at all? Has not Carlyle somewhere said that a belief in destiny is the bias of all earnest minds? 'It is not Nature,' says Fichte, 'it is Freedom itself, by which the greatest and most terrible disorders incident to our race are produced. Man is the cruellest enemy of man.' But the question of moral responsibility here emerges, and it is the possible loosening of this responsibility that so many of us dread. The notion of necessity certainly failed to frighten Bishop Butler. He thought it untrue even absurd — but he did not fear its practical consequences. He showed, on the contrary, in the 'Analogy,' that as far as human conduct is concerned, the two theories of free-will and necessity would come to the same in the end.