Inductive inference is the fundamental method of modern Metaphysical Realism. At one time it was thought that out of concepts we could evolve something that would no longer be a concept. It was thought that the metaphysical reals, which Metaphysical Realism after all requires, could be known by means of concepts. This method of philosophising is now out of date. Instead it is thought that from a sufficiently large number of perceptual facts we can infer the character of the thing-in-itself which lies behind these facts. Formerly it was from concepts, now it is from percepts, that the Realist seeks to evolve the metaphysically real. Because concepts are before the mind in transparent clearness, it was thought that we might deduce from them the metaphysically real with absolute certainty. Percepts are not given with the same transparent clearness. Each fresh one is a little different from others of the same kind which preceded it. In principle, therefore, anything inferred from past experience is somewhat modified by each subsequent experience. The character of the metaphysically real thus obtained can therefore be only relatively true, for it is open to correction by further instances. The character of Von Hartmann’s Metaphysics depends on this methodological principle. The motto on the title-page of his first important book is, “Speculative results gained by the inductive method of Science.”
The form which the Metaphysical Realist at the present day gives to his things-in-themselves is obtained by inductive inferences. Consideration of the process of knowledge has convinced him of the existence of an objectively-real world-nexus, over and above the subjective world which we know by means of percepts and concepts. The nature of this reality he thinks he can determine by inductive inferences from his percepts.
Addition to the Revised Edition (1918).
The unprejudiced study of experience, in perceiving and conceiving, such as we have attempted to describe it in the preceding chapters, is liable to be interfered with again and again by certain ideas which spring from the soil of natural science. Thus, taking our stand on science, we say that the eye perceives in the spectrum colours from red to violet. But beyond violet there lie rays within the compass of the spectrum to which corresponds, not a colour perceived by the eye, but a chemical effect. Similarly, beyond the rays which make us perceive red, there are rays which have only heat effects. These and similar phenomena lead, on reflection, to the view that the range of man’s perceptual world is defined by the range of his senses, and that he would perceive a very different world if he had additional, or altogether different, senses. Those who like to indulge in far-roaming fancies in this direction, for which the brilliant discoveries of recent scientific research provide a highly tempting occasion, may well be led to confess that nothing enters the field of man’s observation except what can affect his senses, as these have been determined by his whole organisation. Man has no right to regard his percepts, limited as these are by his organisation, as in any way a standard to which reality must conform. Every new sense would confront him with a different picture of reality. Within its proper limits, this is a wholly justified view. But if anyone lets himself be confused by this view in the unprejudiced study of the relation of percept and concept, as set forth in these chapters, he blocks the path for himself to a knowledge of man and the world which is rooted in reality. The experience of the essential nature of thought, i.e., the active construction of the world of concepts, is something wholly different from the experience of a perceptible object through the senses. Whatever additional senses man might have, not one would give him reality, if his thinking did not organise with its concepts whatever he perceived by means of such a sense. Every sense, whatever its kind, provided only it is organised by thought, enables man to live right in the real. The fancy-picture of other perceptual worlds, made possible by other senses, has nothing to do with the problem of how it is that man stands in the midst of reality. We must clearly understand that every perceptual picture of the world owes its form to the physical organisation of the percipient, but that only the percepts which have been organised by the living labour of thought lead us into reality. Fanciful speculations concerning the way the world would appear to other than human souls, can give us no occasion to want to understand man’s relation to the world. Such a desire comes only with the recognition that every percept presents only a part of the reality it contains, and that, consequently, it leads us away from its own proper reality. This recognition is supplemented by the further one that thinking leads us into the part of reality which the percept conceals in itself. Another difficulty in the way of the unprejudiced study of the relation we have here described, between percept and concept as elaborated by thought, may be met with occasionally, when in the field of physics the necessity arises of speaking, not of immediately perceptible elements, but of non-perceptible magnitudes, such as, e.g., lines of electric or magnetic force. It may seem as if the elements of reality of which physicists speak, had no connection either with what is perceptible, or with the concepts which active thinking has elaborated. Yet such a view would depend on self-deception. The main point is that all the results of physical research, except illegitimate hypotheses which ought to be excluded, have been gained through perceiving and conceiving. Entities which are seemingly non-perceptible, are referred by the physicists’ sound instinct for knowledge to the field in which actual percepts lie, and they are dealt with in thought by means of the concepts which are commonly applied in this field. The magnitudes in a field of electric or magnetic force are reached, in their essence, by no other cognitive process than the one which connects percept and concept.—An increase or a modification of human senses would yield a different perceptual picture, an enrichment or a modification of human experience. But genuine knowledge could be gained out of this new experience only through the mutual co-operation of concept and percept. The deepening of knowledge depends on the powers of intuition which express themselves in thinking (see page 90). Intuition may, in those experiences in which thinking expresses itself, dive either into deeper or shallower levels of reality. An expansion of the perceptual picture may supply stimuli for, and thus indirectly promote, this diving of intuition. But this diving into the depth, through which we attain reality, ought never to be confused with the contrast between a wider and a narrower perceptual picture, which always contains only half of reality, as that is conditioned by the structure of the knower’s organism. Those who do not lose themselves in abstractions will understand how for a knowledge of human nature the fact is relevant, that physics must infer the existence, in the field of percepts, of elements to which no sense is adapted as it is to colour or sound. Human nature, taken concretely, is determined not only by what, in virtue of his physical organisation, man opposes to himself as immediate percept, but also by all else which he excludes from this immediate percept. Just as life needs unconscious sleep alongside of conscious waking experience, so man’s experience of himself needs over and above the sphere of his sense-perception another sphere—and a much bigger one—of non-perceptible elements belonging to the same field from which the percepts of the senses come. Implicitly all this was already laid down in the original argument of this book. The author adds the present amplification of the argument, because he has found by experience that some readers have not read attentively enough. It is to be remembered, too, that the idea of perception, developed in this book, is not to be confused with the idea of external sense-perception which is but a special case of the former. The reader will gather from what has preceded, but even more from what will be expounded later, that everything is here taken as “percept” which sensuously or spiritually enters into man’s experience, so long as it has not yet been seized upon by the actively constructed concept. No “senses,” as we ordinarily understand the term, are necessary in order to have percepts of a psychical or spiritual kind. It may be urged that this extension of ordinary usage is illegitimate. But the extension is absolutely indispensable, unless we are to be prevented by the current sense of a word from enlarging our knowledge of certain realms of facts. If we use “percept” only as meaning “sense-percept,” we shall never advance beyond sense-percepts to a concept fit for the purposes of knowledge. It is sometimes necessary to enlarge a concept in order that it may get its appropriate meaning within a narrower field. Again, it is at times necessary to add to the original content of a concept, in order that the original thought may be justified or, perhaps, readjusted. Thus we find it said here in this book: “An idea is nothing but an individualised concept.” It has been objected that this is a solecism. But this terminology is necessary if we are to find out what an idea really is. How can we expect any progress in knowledge, if every one who finds himself compelled to readjust concepts, is to be met by the objection: “This is a solecism”?