III THEORY OF KNOWLEDGE SINCE KANT

But, even if these various propositions were correct, or led to correct formulations of the problem, it would still be impossible to discuss them at the outset of the Theory of Knowledge. For, they all belong, as positive and definite cognitions, within the realm of knowledge. To say that my knowledge extends, in the first instance, only to my ideas, is to express in a perfectly definite judgment something which I know. In this judgment I qualify the world which is given to me by the predicate “existing in the form of idea.” But how am I to know, prior to all knowledge, that the objects given to me are ideas?

The best way to convince ourselves of the truth of the assertion that this proposition has no right to be put at the head of the Theory of Knowledge, is to retrace the way which the human mind must follow in order to reach this proposition, which has become almost an integral part of the whole modern scientific consciousness. The considerations which have led to it are systematically summarised, with approximate exhaustiveness, in Part I of Eduard von Hartmann’s treatise, Das Grundproblem der Erkenntnistheorie. His statement, there, may serve as a sort of guiding-thread for us in our task of reviewing the reasons which may lead to the acceptance of this proposition.

These reasons are physical, psycho-physical, physiological, and properly philosophical.

The Physicist is led by observation of the phenomena which occur in our environment when, e.g., we experience a sensation of sound, to the view that there is nothing in these phenomena which in the very least resembles what we perceive immediately as sound. Outside, in the space which surrounds us, nothing is to be found except longitudinal oscillations of bodies and of the air. Thence it is inferred that what in ordinary life we call “sound” or “tone” is nothing but the subjective reaction of our organism to these wave-like oscillations. Similarly, it is inferred that light and colour and heat are purely subjective. The phenomena of colour-dispersion, of refraction, of interference, of polarisation, teach us that to the just-mentioned sensations there correspond in the outer space certain transverse oscillations which we feel compelled to ascribe, in part to the bodies, in part to an immeasurably fine, elastic fluid, the “ether.” Further, the Physicist is driven by certain phenomena in the world of bodies to abandon the belief in the continuity of objects in space, and to analyse them into systems of exceedingly minute particles (molecules, atoms), the size of which, relatively to the distances between them, is immeasurably small. Thence it is inferred that all action of bodies on each other is across the empty intervening space, and is thus a genuine actio in distans. The Physicist believes himself justified in holding that the action of bodies on our senses of touch and temperature does not take place through direct contact, because there must always remain a definite, if small, distance between the body and the spot on the skin which it is said to “touch.” Thence it is said to follow that what we sense as hardness or heat in bodies is nothing but the reactions of the end-organs of our touch- and temperature-nerves to the molecular forces of bodies which act upon them across empty space.

These considerations from the sphere of Physics are supplemented by the Psycho-physicists with their doctrine of specific sense-energies. J. Müller has shown that every sense can be affected only in its own characteristic way as determined by its organisation, and that its reaction is always of the same kind whatever may be the external stimulus. If the optical nerve is stimulated, light-sensations are experienced by us regardless of whether the stimulus was pressure, or an electric current, or light. On the other hand, the same external phenomena produce quite different sensations according as they are perceived by different senses. From these facts the inference has been drawn that there occurs only one sort of phenomenon in the external world, viz., motions, and that the variety of qualities of the world we perceive is essentially a reaction of our senses to these motions. According to this view, we do not perceive the external world as such, but only the subjective sensations which it evokes in us.

Physiology adds its quota to the physical arguments. Physics deals with the phenomena which occur outside our organisms and which correspond to our percepts. Physiology seeks to investigate the processes which go on in man’s own body when a certain sensation is evoked in him. It teaches us that the epidermis is wholly insensitive to the stimuli in the external world. Thus, e.g., if external stimuli are to affect the end-organs of our touch-nerves on the surface of our bodies, the oscillations which occur outside our bodies have to be transmitted through the epidermis. In the case of the senses of hearing and of sight, the external motions have, in addition, to be modified by a number of structures in the sense-organs, before they reach the nerves. The nerves have to conduct the effects produced in the end-organs up to the central organ, and only then can take place the process by means of which purely mechanical changes in the brain produce sensations. It is clear that the stimulus which acts upon the sense-organs is so completely changed by the transformations which it undergoes, that every trace of resemblance between the initial impression on the sense-organs and the final sensation in consciousness must be obliterated. Hartmann sums up the outcome of these considerations in these words: “This content of consciousness consists, originally, of sensations which are the reflex responses of the soul to the molecular motions in the highest cortical centres, but which have not the faintest resemblance to the molecular motions by which they are elicited.”

If we think this line of argument through to the end, we must agree that, assuming it to be correct, there survives in the content of our consciousness not the least element of what may be called “external existence.”

Now let us ask ourselves, How do we come by such a view? The bare skeleton of the line of thought which leads to it is as follows. Supposing an external world exists, we do not perceive it as such but transform it through our organisation into a world of ideas. This is a supposition which, when consistently thought out, destroys itself. But is this reflection capable of supporting any positive alternative? Are we justified in regarding the world, which is given to us, as the subjective content of ideas because the assumptions of the naïve consciousness, logically followed out, lead to this conclusion? Our purpose is, rather, to exhibit these assumptions themselves as untenable. Yet, so far we should have found only that it is possible for a premise to be false and yet for the conclusion drawn from it to be true. Granted that this may happen, yet we can never regard the conclusion as proved by means of that premise.

It is usual to apply the title of “Naïve Realism” to the theory which accepts as self-evident and indubitable the reality of the world-picture which is immediately given to us. The opposite theory, which regards this world as merely the content of our consciousness, is called “Transcendental Idealism.” Hence, we may sum up the outcome of the above discussion by saying, “Transcendental Idealism demonstrates its own truth, by employing the premises of the Naïve Realism which it seeks to refute.” Transcendental Idealism is true, if Naïve Realism is false. But the falsity of the latter is shown only by assuming it to be true. Once we clearly realise this situation, we have no choice but to abandon this line of argument and to try another. But are we to trust to good luck, and experiment about until we hit by accident upon the right line? This is Eduard von Hartmann’s view when he believes himself to have shown the validity of his own epistemological standpoint, on the ground that his theory explains the phenomena whereas its rivals do not. According to his view, the several philosophical systems are engaged in a sort of struggle for existence in which the fittest is ultimately accepted as victor. But this method appears to us to be unsuitable, if only for the reason that there may well be several hypotheses which explain the phenomena equally satisfactorily. Hence, we had better keep to the above line of thought for the refutation of Naïve Realism, and see where precisely its deficiency lies. For, after all, Naïve Realism is the view from which we all start out. For this reason alone it is advisable to begin by setting it right. When we have once understood why it must be defective, we shall be led upon the right path with far greater certainty than if we proceed simply at haphazard.