When the Metaphysical Realist asserts that, beside the ideal relation between the perceived object and the perceiving subject, there must be a real relation between the percept as “thing-in-itself” and the subject as “thing-in-itself” (the so-called individual mind), he is basing his assertion on the false assumption of a real process, imperceptible but analogous to the processes in the world of percepts. Further, when the Metaphysical Realist asserts that we stand in a conscious ideal relation to our world of percepts, but that to the real world we can have only a dynamic (force) relation, he repeats the mistake we have already criticised. We can talk of a dynamic relation only within the world of percepts (in the sphere of the sense of touch), but not outside that world.
Let us call the view which we have just characterised, and into which Metaphysical Realism merges when it discards its contradictory elements, Monism, because it combines one-sided Realism and Idealism into a higher unity.
For Naïve Realism, the real world is an aggregate of percepts; for Metaphysical Realism, reality belongs not only to percepts but also to imperceptible forces; Monism replaces forces by ideal relations which are supplied by thought. These relations are the laws of nature. A law of nature is nothing but the conceptual expression for the connection of certain percepts.
Monism is never called upon to ask whether there are any principles of explanation for reality other than percepts and concepts. The Monist knows that in the whole realm of the real there is no occasion for this question. In the perceptual world, as immediately apprehended, he sees one-half of reality; in the union of this world with the world of concepts he finds full reality. The Metaphysical Realist might object that, relatively to our organisation, our knowledge may be complete in itself, that no part may be lacking, but that we do not know how the world appears to a mind organised differently from our own. To this the Monist will reply, Maybe there are intelligences other than human; and maybe also that their percepts are different from ours, if they have perception at all. But this is irrelevant to me for the following reasons. Through my perceptions, i.e., through this specifically human mode of perception, I, as subject, am confronted with the object. The nexus of things is thereby broken. The subject reconstructs the nexus by means of thought. In doing so it re-inserts itself into the context of the world as a whole. As it is only through the Self, as subject, that the whole appears rent in two between percept and concept, the reunion of those two factors will give us complete knowledge. For beings with a different perceptual world (e.g., if they had twice our number of sense-organs) the nexus would appear broken in another place, and the reconstruction would accordingly have to take a form specifically adapted to such beings. The question concerning the limits of knowledge troubles only Naïve and Metaphysical Realism, both of which see in the contents of mind only ideal representations of the real world. For, to these theories, whatever falls outside the subject is something absolute, a self-contained whole, and the subject’s mental content is a copy which is wholly external to this absolute. The completeness of knowledge depends on the greater or lesser degree of resemblance between the representation and the absolute object. A being with fewer senses than man will perceive less of the world, one with more senses will perceive more. The former’s knowledge will, therefore, be less complete than the latter’s.
For Monism, the situation is different. The point where the unity of the world appears to be rent asunder into subject and object depends on the organisation of the percipient. The object is not absolute but merely relative to the nature of the subject. The bridging of the gap, therefore, can take place only in the quite specific way which is characteristic of the human subject. As soon as the Self, which in perception is set over against the world, is again re-inserted into the world-nexus by constructive thought, all further questioning ceases, having been but a result of the separation.
A differently constituted being would have a differently constituted knowledge. Our own knowledge suffices to answer the questions which result from our own mental constitution.
Metaphysical Realism must ask, What is it that gives us our percepts? What is it that stimulates the subject?
Monism holds that percepts are determined by the subject. But in thought the subject has, at the same time, the instrument for transcending this determination of which it is itself the author.
The Metaphysical Realist is faced by a further difficulty when he seeks to explain the similarity of the world-views of different human individuals. He has to ask himself, How is it that my theory of the world, built up out of subjectively determined percepts and out of concepts, turns out to be the same as that which another individual is also building up out of these same two subjective factors? How, in any case, is it possible for me to argue from my own subjective view of the world to that of another human being? The Metaphysical Realist thinks he can infer the similarity of the subjective world-views of different human beings from their ability to get on with one another in practical life. From this similarity of world-views he infers further the likeness to one another of individual minds, meaning by “individual mind” the “I-in-itself” underlying each subject.
We have here an inference from a number of effects to the character of the underlying causes. We believe that after we have observed a sufficiently large number of instances, we know the connection sufficiently to know how the inferred causes will act in other instances. Such an inference is called an inductive inference. We shall be obliged to modify its results, if further observation yields some unexpected fact, because the character of our conclusion is, after all, determined only by the particular details of our actual observations. The Metaphysical Realist asserts that this knowledge of causes, though restricted by these conditions, is quite sufficient for practical life.