a) A Berkeleyan Perspective

In connection with Reid’s philosophy, I spoke of stepping out of Plato’s cave into a bright spring morning. To enter Kant’s philosophy is not like returning to the cave. It is like getting lost in a fog. To the famous “der Kant hat sie alle verwirret,” we must add: “weil er so verwirret war”! (H. Vaihinger, Kommentar zu Kant’s Kritik der reinen Vernunft, vol. 2, p. 502).

Kant, it seems, was not too familiar with Berkeley’s philosophy. Yet, I shall start our inquiry by reminding you of Berkeley’s basic contention, namely, that the so-called primary qualities (size, shape, motion, rest, and number) are just as much mere ideas (sensations) in minds as the so-called secondary qualities. Shape is no better off than color. This means that all of the sensible properties of perceptual objects are mere ideas. Add to this the ontological thesis that a perceptual object is but a bundle or collection of sensible properties, and you get what I have called Berkeley’s main argument for idealism. Idealism thus follows straightforwardly from two quite simple assertions.

One can look at Kant’s philosophy from many different perspectives. From one, a less historical and more structural perspective, Kant can be seen to provide a further argument, and quite a powerful one, for Berkeley’s contention that primary qualities are just as “subjective” as secondary ones. Berkeley pointed out that shape suffers just as much from the relativity of sensing as color. Kant’s argument is of an entirely different sort. Roughly, it states that primary qualities are just as “subjective” as secondary ones because we have synthetic knowledge a priori about them. Space and time, Kant holds, are merely “subjective.” They are the forms of our sensibility. Since they are the forms of our sensibility, they apply automatically to the objects formed by them. This line of thought is so familiar that I need not spell it out in detail. But let me add that I do not wish to deny that there is an important difference between space and time, on the one hand, and “ordinary” sensations, on the other. Nor do I wish to belittle the difference between Berkeley’s task and the completely different problem which Kant poses in terms of these forms of intuition. However, the fact remains that the primary qualities of shape, size, number, etc., that is, spatial, temporal, and numerical attributes, are placed in the mind.

The situation is quite different in regard to Berkeley’s ontological thesis. Far from rejecting the category of (material) substance, Kant emphasizes its importance for the formation of objects. The category of substance, in connection with the forms of intuition, produces out of the manifold of sensations a perceptual object. Berkeley’s apple is not just a bundle of sensations given to the mind as a finished bundle, but is the product of an elaborate mental process. Nevertheless, the material and the form of this product is purely mental. Kant’s apple, just like Berkeley’s, is a mental thing. Kant’s theory merely adds a very complicated and rather nebulous mental process of production to Berkeley’s simple idealism. The facts, of course, rebel in either case: An apple is neither a simple collection of sensations, nor is it a most elaborate construction out of such sensations.

But there is, as we know, a joker in Kant’s deck: the Ding an sich. The Ding an sich, from our structural rather than historical point of view, is what remains if we abstract from the perceptual object all of its perceptual properties, namely, a bare substance. It is the wax, as conceived of by Descartes, divorced from all of its sensible properties. As such, it cannot be known by the senses, but only by the understanding. But Kant also stresses the causal role of this “substance behind the sensible properties.” He sometimes talks as if the Ding an sich were somehow the cause of our sensations. The unknown substance which supports sensible properties does not play this causal role; it does not cause its properties, but merely props them up. Kant’s Ding an sich is more like Berkeley’s God who is ultimately responsible for our experiencing the particular bundles of sensations which we do experience.

From our Berkeleyan perspective, we get the following picture of Kant’s philosophy. Firstly, Kant confirms Berkeley’s contention that primary qualities are as mental as secondary ones. He adds a whole new dimension to the grounds for this contention by claiming that space and time are the forms of our intuitions. Secondly, as a result, Kant agrees with Berkeley’s view that perceptual objects are mental things. In this respect, he is a Berkeleyan idealist. However, and thirdly, while Berkeley thinks of the mental thing as a given collection of sensations, Kant assumes that it is the product of a great deal of mental activity. The so-called primary qualities play an important epistemological role in this activity. They have an epistemological function as (a) the forms of intuition (shape, size, duration, etc.), and (b) the categories (substance, force, divisibility, etc.). Fourthly, while Berkeley holds that the flow of bundles of sensations is caused by God, Kant assumes that the mind receives the raw material for its productivity from an unknown Ding an sich.

If this perspective illuminates Kant’s basic system, then it follows that a realist must not only turn back the Berkeleyan arguments for the mental nature of primary qualities, but also refute Kant’s arguments for the synthetic a priori nature of our knowledge of space and time. He must, in other words, address himself to the problem of mathematical knowledge as Kant conceives of it. It is part of the genius of Kant’s philosophy that in it idealism cannot be divorced from this problem.

How did Kant view his relationship with Berkeley? Kant agrees that “all bodies, together with the space in which they are, must be considered nothing but mere presentations in us, and exist nowhere but in our thoughts” (Prolegomena, par. 13, remark ii). But Kant goes on to point out that, according to his philosophy, there really exist in the nonmental world certain Dinge an sich: “Consequently I grant by all means that there are bodies without us, that is, things which, though quite unknown to us as to what they are in themselves, we yet know by the representations which their influence on our sensibility procures us” (Kant, 1957). And then he turns the table on us by pointing out that Locke and others have held that the secondary qualities are mental, without having been called, for that reason, idealists. The only difference between Locke and himself, Kant says, is that he, in distinction to Locke, claims that “all the properties which constitute the intuition of a body belong merely to its appearance” (Kant, 1957). This view, Kant claims, does not destroy the existence of the thing which so appears to the senses, as genuine idealism does. Hence, so Kant seems to conclude, his view is no more idealistic than Locke’s.

There is no point arguing about the word ‘idealism’. Kant’s view is quite different from Locke’s and Berkeley’s. There is, we must always remind ourselves, the much maligned Ding an sich in Kant’s philosophy. Yet, Kant’s appeal to Locke does not touch upon the real issue. No view, no matter how similar or dissimilar it may be to Berkeley’s or Locke’s views, can be correct if it denies the non-mental nature of perceptual objects and their properties. From our point of view, Kant’s “realism” is a sham. It substitutes for the exciting fullness of the perceptual world the arid realm of unknown Dinge an sich. If weighed on the scale of truth, it does not beat Berkeley’s undisguised idealism by much.

What is at issue is not the quality of semantic acrobatics with the term ‘idealism’, but rather what Kant himself clearly describes in the following paragraph from the same place:

I should be glad to know what my assertion must be in order to avoid idealism. Undoubtedly, I should say that the representation of space is not only perfectly comfortable to the relation which our sensibility has to objects—that I have said—but that it is quite similar to the object—an assertion in which I can find as little meaning as if I said that the sensation of red has a similarity to the property of cinnibar which excites this sensation in me.

(Kant, 1957)

What Kant here pronounces to be meaningless is precisely the view which I have defended, although not quite in the way in which he formulates it. The red sensation is indeed “similar” to the property of cinnibar which causes me to have it. In fact, it is this very same property, namely, a certain shade of the color red. Similarly, some of the spatial relations among perceptual objects are roughly the same, under normal circumstances, as the spatial relations among my sensations; sensations which are caused by those perceptual objects. We may speculate that Kant does not share our understanding of the situation because he, like many other philosophers, thinks of a shade of red as a sensation and not, as we do, as a property of a sensation. Nor does he believe that the property of cinnibar, which causes us to experience the sensation, is the shade of red just mentioned. Rather, he holds that this property of cinnibar is some kind of “physical” quality of the cinnibar which causes us to have the sensation of [sic] red. This insidious conception of the situation is by now so familiar to us that we need not dwell on it. But something else deserves special emphasis. Notice that Kant here compares the sensation of red, not with an unknown quality of the Ding an sich, but with a physical property of cinnibar. What suddenly appears here on the philosophical stage is something we have not encountered before, namely, a “middle thing” located somewhere between sensations and their combinations, on the one hand, and the Dinge an sich, on the other. We shall return to this phantom of the philosophical theater in a moment.

There are two further references to Berkeley in the Critique of Pure Reason. In B 69-70, Kant defends himself against the accusation that his conception of intuition as mere appearance transforms the world into mere illusion. He tries here, as in the Prolegomena, to make a sharp distinction between appearance and illusion. Much of what he says at this point is not clear (cf. Vaihinger, vol. 2, pp. 486-94). Fortunately, we need not try to make sense of it. From the perspective we have chosen, it is clear that what matters is not the distinction between appearance and illusion, but the distinction between the mental and the non-mental. The question is not whether or not Kant transforms the world into mere illusion, but whether or not perceptual objects are transformed into mental constructions. In regard to Berkeley, Kant remarks that it is no wonder that Berkeley turned bodies into mere illusion, since he started out by thinking of space and time as belonging objectively to bodies. Kant repeats here his standard claim that any conception of space and time as mind-independent entities must lead to contradictory conclusions about their natures. Needless to say, we do not accept this claim. Berkeley’s apple has certain spatio-temporal attributes (properties and relations) just as “objectively” as it has certain other perceptual properties (color, taste, etc.). The assumption that the shape of Oscar is just as much a mind-independent property of it as its color leads neither to contradiction nor to confusion.

b) The Special Nature of Space

From our Berkeleyan perspective, Kant’s view about space comes down to the claim that such alleged primary qualities as size and shape are just as mental as the secondary qualities of color, taste, etc. Shape, we may sum it up, is just as mental as color. However, Kant rejects this assimilation in the Critique of Pure Reason (A 28-29, B 44-45), and we must take a look at the following important passage:

(A 28) With the sole exception of space there is no subjective representation, referring to something outer, which could be entitled [at once] objective [and] a priori. This subjective condition of all outer appearances cannot, therefore, be compared to any other. The taste of a wine does not belong to the objective determinations of the wine, not even if by the wine as an object we mean the wine as appearance, but to the special constitution of sense in the subject that tastes it. Colours are not properties of the bodies to the intuition of which they are attached, but only modifications of the sense of sight, which is affected in a certain manner by light. Space, on the other hand, as condition of outer objects, necessarily belongs to their appearance or intuition. Taste and colors are not necessary conditions under which alone objects can be for us objects of the senses. They are connected with the appearances only as effects accidentally added by the particular constitution of the sense organs. Accordingly, they are not a priori representations, but are grounded in sensations, and, indeed, in the case of taste even upon feeling (pleasure and pain), as an effect of sensation. Further, no one can have a priori a representation of a colour or of any taste; whereas, since space concerns only the pure form of intuition, and therefore involves no sensation whatsoever, and nothing empirical, all kinds and determinations of space can and must be represented a priori, if concepts of figures and of their relations are to arise. Through space alone is it possible that things should be other objects to us.

(Kant, 1965)

Kant’s first sentence asserts that space is the only subjective representation which is (a) objective and (b) a priori. Color, we take it, is neither. Kant argues that space is objective while color is not by asserting that colors are not properties of the bodies to the intuition of which they are attached, while space necessarily belongs to their appearance or intuition. Colors, I take him to be saying, do admittedly not belong to perceptual objects, but are merely sensations in minds. Space, on the other hand, is a property of perceptual objects; even as appearances, such objects have spatial attributes (shape, size, spatial relations). In other words, Kant here invokes the distinction between primary and secondary qualities to make his point. It is as if he had simply forgotten his whole philosophy, falling back to the level of what passes for scientific common sense. Everyone knows, he seems to be arguing, that color is only in the mind, while shape and size are really properties of “outer” non-mental things. Thus while the latter are objective, the former are merely subjective. But the distinction does not fit into Kant’s philosophy. Or, rather, as I shall argue in a moment, it can only be made to fit if we turn his philosophy into a Rube Goldberg type of contraption with layers of unknown things and levels of unconscious processes. What I wish to call attention to at this point is the incredible power which the distinction between primary and secondary qualities has had over the minds of philosophers, including Kant’s.

Color, in distinction to space, is supposedly not an a priori representation. This assertion leads into the thicket of Kant’s philosophy, and a full discussion of it would lead us too far astray. But a few remarks are in order. Firstly, what is at stake is the Kantian dogma that there can be no sensations of space (and time), a dogma to which we shall return in a moment. Secondly, we must note that what Kant here contrasts with each other is not shape with color, but rather space with color. And this raises the all-important question of what this space is. He says that it is something that “concerns only the pure form of intuition.” Is it then a pure form of intuition? Well, I shall not get lost in Kant’s fog, but merely note that we can distinguish among at least three notions of space in Kant: (1) Space as form of intuition, (2) space as (pure) intuition (content of intuition; this is the space of geometry; it is one individuum), and (3) space in the form of spatial properties and relations. Perhaps these three notions can somehow be combined in the following picture, keeping in mind that this picture does not agree with many of Kant’s pronouncements. The mind has the ability to order things spatially; this is a function of space as a form of intuition. What results from this arrangement of intuitions is the empirical, relative space of perception; things are perceived as having certain shapes and as standing in certain spatial relations to each other. When the mind goes to work on this product of the spatial form, it abstracts from it the one absolute space. This abstraction is the space of physics (cf. Vaihinger, vol. 2, p. 230). However, this interpretation leads immediately to difficulties for Kant’s philosophy. Where does this leave the space of mathematics (geometry)? Furthermore, and more importantly, if the space of geometry is said to be gotten in the way in which the space of physics is abstracted, then geometry is no longer known a priori! It is then a matter of experience.

Space, in our view, consists of and is exhausted by spatial properties, such as size and shape, together with the various spatial relations. Kant is very vague about these obvious spatial features of the world. It has been noted, for example, that he never tries to explain why a particular perceptual object is perceived to be round while another is perceived to be square. Obviously, the alleged fact that intuition is spatial, that it must pass through the spatial filter, does not explain why we perceive a particular perceptual object as round rather than square. Nor is this circumstance explained by the presumed fact that we have a pure intuition of an infinite space. Be that as it may, it is at any rate clear that Kant says very little about the particular problem which has our attention, namely, the problem of how shape compares with color in regard to the distinction between primary and secondary qualities.

Let us next look at the relevant passage in the second edition of the Critique:

(B 45) The above remark is intended only to guard anyone from supposing that the ideality of space as here asserted can be illustrated by examples so altogether insufficient as colors, taste, etc. For these are rightly regarded not as properties of things, but only as changes in the subject, changes which may, indeed, be different for different men. In such examples as these, that which originally is itself only appearance, for instance, a rose, is being treated by the empirical understanding as a thing in itself, which, nevertheless, in respect of its color, can appear differently to every observer. The transcendental concept of appearances in space, on the other hand, is a critical reminder that nothing intuited in space is a thing in itself, that space is not a form inhering in things in themselves as their intrinsic property, that objects in themselves are quite unknown to us, and that what we call other objects are nothing but mere representations of our sensibility, the form of which is space. The true correlate to sensibility, the thing in itself, is not known, and cannot be known, through these representations; and in experience no question is ever asked in regard to it.

(Kant, 1965)

Kant claims that the ideality of space is not the ideality of color; for while color is merely subjective, even for the empirical understanding, space is not. While the color of Berkeley’s apple is a mere sensation in the mind, we could say, its shape is not. In short, in order to guard against a confusion of the ideality of space with the ideality of color, Kant appeals to the distinction between primary and secondary qualities. He seems to base this distinction on the argument from the relativity of sensing. The color of the rose, he claims, can appear differently to different observers. In the spirit of Berkeley, we would wish to point out to Kant that the same can be said about the shape and the size of the rose. Of course, Berkeley’s spirit is not the spirit of our philosophy. We do not even accept the premise that the perceived color of the rose must vary from observer to observer. But if we accepted this fundamental premise of the argument, then we would also have to insist that the spatial characteristics of the rose vary in the same fashion. Even in the second edition of the Critique of Pure Reason, Kant appeals to the traditional distinction between primary and secondary qualities and to one of the traditional arguments for it.

Notice, lastly, the unequivocal commitment to idealism: “what we call outer objects are nothing but mere representations of our sensibility.” The German word is of course Vorstellungen. A perceptual object, therefore, is nothing but a Vorstellung. It is true that there is also the Ding an sich. But this part of Kant’s view rests on nothing more than blind “Humean” belief. From a systematic point of view, the Ding an sich is merely an appendage of the body of Kant’s philosophy.

Kant tries to defend his blend of idealism in the well-known second remark of paragraph 13 of the Prolegomena which we have mentioned before. What is so remarkable about this passage is that Kant does not invoke the distinction between primary and secondary qualities, but, quite to the contrary, treats space on a par with color, taste, etc. Kant, following in the footsteps of Berkeley, tries to put a reasonable face on the absurd view that a perceptual object, Berkeley’s apple, for instance, is a representation in a mind. We see here the same idealistic trick at work which we have exposed on earlier occasions. “Look,” Kant says to us, “you have already admitted that color is a mere sensation in the mind. Yet you also believe that there are perceptual objects and, hence, you are not an idealist. Now, I hold that other properties as well—shape, size, etc.—are mental. Yet I too believe that there are ‘external things.’ So I deserve to be called an idealist no more than you do.” Kant has a point, but the point is not what he believes it to be. What his line of reasoning shows, if it shows anything, is that Berkeley’s contention is correct: If you admit that color is only in the mind, you may as well also admit that shape is only in the mind. But to admit either, we must emphasize against Kant, is to be an idealist or, more cautiously, it is to make an idealistic view inevitable. “External objects” without colors, tastes, etc., are simply not the perceptual objects which a realist defends. And perceptual objects without colors, tastes, etc., and also without shapes, sizes, etc., are even less like them.

Let us now pause for a moment in our main discussion and touch upon a more peripheral issue, an issue which, nevertheless, has played a major role in the history of philosophy. I have in mind Kant’s dogma “That in which alone the sensations can be ordered, cannot itself be sensation” (Kant, 1965, A 20, B 34). In other words, the dogma that there are no spatial sensations. If Kant were correct, then there would indeed exist quite a difference between color, on the one hand, and space, on the other. But is he? Why does he accept the dogma? Since Kant does not argue for it explicitly, we can only speculate about his reason.

But first we must remind ourselves of how our conception of sensations differs from the commonly accepted one. A color shade, for instance, the color olive green, is commonly said to be a sensation. But the color is clearly a property, and this raises the question of what it is a property of. If one believes in Berkeley and assumes that an olive, for example, is nothing but a bundle of properties, and that these properties are sensations, then we have an answer: The sensation olive green is a property of an olive. Sensations turn out to be properties of perceptual objects. But assume that we do not accept the bundle view of individual things. What then is this color a property of? This question is seldom if ever raised by those who think of colors (and other perceptual properties) as sensations. No wonder, for it is obvious that there is no plausible answer to it. Olive green cannot very well be a property of the mind (mental substance), for this would imply that the mind is colored (and has a taste, etc.). Nor can it be a property of olives, for this would imply that olives have “mental” properties. But if so-called color sensations are properties neither of minds nor of nonmental individuals, what are they properties of? According to our view, the dilemma does not appear. Colors are not sensations at all, for sensations are individual (mental) things, while colors are not. Colors are properties of certain sensations, and they are also properties of certain perceptual objects. Olive green is a property of olives, and also a property of certain sensations which we experience when we look at olives under ordinary conditions. Thus it is, properly speaking, neither mental nor nonmental. But there are mental things, sensations, which have this color, and there are also nonmental things, perceptual objects, which are olive green.

Having refreshed our memory of this important point, let us return to what a moment ago I called Kant’s dogma. Why can there be no sensation of space? Well, we have already noted that Kant has at least three different conceptions of space. There is, first of all, space as the form of outer intuition. I can make some sense of this phrase “form of outer intuition,” if I translate it into “spatial intuition,” that is, if I assume that there is a kind of intuition which is spatial. So-called outer intuition is presumably of this sort. We may call this notion of space, tongue in cheek, the “adverbial view.” I shall concede that space, so conceived, cannot be a matter of sensation. We simply do not have sensations of (properties of) acts of intuition. Mental acts, of whatever kind, are not the sort of thing which causes us to experience sensations. This leads us to the second conception of space, space as an absolute, infinite, individual thing. (For passages from Kant, see Vaihinger, vol. 2, pp. 71-72.) Space as an empty container to be filled with sensations does not seem to be the sort of thing of which we can have sensations. Thus I am willing to agree, again, that there are no sensations of space so conceived.

But what about spatial properties and relations? Consider shape first. It seems to me to be obvious that a sensation may have a shape just as well as a color. In this straightforward sense, there are “shape sensations” just as there are “color sensations.” Of course, what we really mean by these common but misleading expressions is that there are shaped sensations just as there are colored sensations. And there are also, we should add, sensations of shape just as there are sensations of color. That is, there are shaped sensations caused by shaped perceptual objects, just as there are colored sensations caused by colored perceptual objects.

But sensations do not just have shape and color, they also stand in spatial relations to each other. A green and round sensation, for example, may be between two red and square sensations. And just as we have somewhat perversely agreed to speak of a round sensation when a sensation is round, so we could speak of a between sensation when a sensation is between two other sensations. Thus we come to the conclusion that Kant is mistaken. There are spatial sensations just as there are color sensations; for there are round sensations and between sensations. There are also, as should be clear, sensations of space in the sense that there are sensations of spatial objects.

However, we must keep in mind that the case for spatial relations is quite different from the case for spatial properties. Until very recently, it has been philosophical dogma that relations are not part of the furniture of the world. Of relations, Berkeley tells us, we have not ideas but notions. And the reason is that knowledge of relations, as distinct from knowledge of (ordinary) properties, requires an activity of the mind. Relations, according to the traditional view, are created by mental acts of comparison. What is given, on the level of sensations, are certain properties, but no relations. Only if the mind goes to work on these given sensations, do relations come into being. According to this hazy picture, the mind orders and arranges the sensations presented to it and, by doing so, creates the relations among them.

Perhaps it is this kind of picture which moved Kant to say that “that in which alone the sensations can be ordered, cannot itself be sensation.” It may rest ultimately on the conviction that while sensations are given to the mind, their order is not. But we insist that just as the colors and shapes of sensations are not created by the mind, so is their arrangement and order not produced by the mind. Sensations are experienced as having certain properties and as standing in certain relations to each other.

Sensations are mental. Yet, they can have shapes and stand in spatial relations to each other. It follows that some mental things “are in space.” Our view contradicts a version of Descartes’s assertion that the mind is not extended. More precisely, it contradicts the widespread view that mental things cannot be spatial. However, Descartes’s view is true of mental acts. A wish or a desire, it is clear, cannot appear between two other things. If a mind consisted of nothing else but of mental acts, if it were nothing but thought, to speak with Descartes, then it would indeed be true that mental things (a mind) are not spatial. But a mind also contains sensations, and insofar as it contains them, it is spatial in the sense which we have explained above.

c) The Double Affection Interpretation

I have painted a picture—some would undoubtedly say a caricature—of Kant as a sophisticated Berkeleyan idealist who (a) postulates a Ding an sich, (b) holds a confused and confusing view of space, and (c) poses an enduring challenge to theories of mathematical knowledge. But there is also a more realistic side to Kant’s philosophy. This realism appears in the later stages of Kant’s philosophical development. What I have so far discussed, one might say, is the early Kant, the Kant of the Inauguraldissertation and of the first edition of the Critique of Pure Reason. What emerges in his later philosophy is a new kind of entity, a “Mittelding,” a thing situated somewhere between the Ding an sich and the perceptual object conceived of as a mental construction. What emerges with time is, to use our terminology, a physical object, distinct both from the Ding an sich and the perceptual object. This emergence is signaled by Kant’s distinction between primary and secondary qualities in the passages quoted earlier as well as in other places (see Erich Adickes, Kants Lehre von der doppelten Affektion unseres Ich, pp. 67-74).

In the passage from A 28, for example, Kant says that “Colors are not properties of the bodies to the intuition of which they are attached, but only modifications of the sense of sight, which is affected in a certain manner by light” (my italics). What affects the sense of sight is thus not the Ding an sich, but light. One may therefore conclude that Kant holds that in addition to the unknowable Ding an sich and the perceptual object, which is constructed out of color, taste, etc., there also exists a physical entity, light, which is identical neither with the former nor with the latter. In B 45 we read, similarly, that colors and taste “are rightly regarded, not as properties of things, but only as changes in the subject, changes which may, indeed, be different for different men” (my italics). When they are so regarded, Kant continues, then the perceptual object, a rose, “is being treated by the empirical understanding as a thing in itself, a thing which, nevertheless, in respect of its color, can appear differently to different observers.” Kant seems to accept here, too, the distinction between primary and secondary qualities and, with it, the rose as a “Mittelding” somewhere between the Ding an sich and the perceptual object.

How seriously shall we take these passages? It all depends on what we wish Kant had held. I have already indicated that I do not believe there is such a thing as the Kantian philosophy, the Kantian system. There are, rather, Kantian themes, themes which often are not clearly stated and which may even contradict each other. But if one cannot resist the temptation to find the one and only true Kantian philosophy—and it is surely amazing how many brilliant people have succumbed to this temptation—then one may read into Kant’s allusions to the primary-secondary distinction the makings of an idealism infinitely more sophisticated than Berkeley’s. One may then see one’s way clear to make peace between Kant’s philosophy, on the one hand, and the teaching of modern science, on the other. The distinction between primary and secondary qualities, I have emphasized, is a child of modern science. While color and taste are only in the mind, the Cartesian scientist holds, shape, number, motion, etc. are real properties of physical objects (atoms). Now, if Kant had made this distinction, he would have been in tune with science; he would have been in tune with the conviction that even though color and taste are only in the mind, “out there,” in the nonmental world, there really exist certain physical things in genuine space. Kant, one could then assert, was no Berkeleyan idealist, for although he holds that perceptual objects are only mental, he also holds that there are nonmental physical objects. This interpretation of Kant kills two birds with one stone: It avoids the charge that Kant was a Berkeleyan idealist and it brings Kant into harmony with physics.

Adickes has worked out such an interpretation. He takes the point of view of “scientific realism”:

According to scientific realism, however, what affects us are not the colored, sounding, hard or soft objects of sense which surround us. Rather, philosophers and scientists have agreed since Kepler’s, Galileo’s, and Descartes’s time that all qualities of sense are only subjectively founded properties, not belonging to the things themselves, but originating in our mind as its reaction and, hence, only existing in the form of contents of consciousness. Bodies were conceived of as collections of atoms or corpuscles, and the whole world around us was thought of as diffused into a series of continuous motions, be it of the bodies themselves or of their smallest mass parts.

(Adickes, p. 37)

Adickes argues brilliantly that the usual interpretations of Kant clash with scientific realism, for according to these interpretations what affects us is the Ding an sich, not the physical object. But if “one eliminates the empirical affection [by the physical object] and retains only the transcendental one, then the world of experience would lose all genuine objectivity and reality. There would be no real connections, no real mutual influence among bodies; the only causes would be the things in themselves” (Adickes, p. 40). In short, Adickes rejects the view that the nonmental world consists exclusively of Dinge an sich. Instead, he develops the so-called double affection interpretation, according to which the things in themselves affect, not the empirical self, but the so-called I in itself. The result of this over-arching interaction is the creation of the world of physics and of the empirical self. But the latter interact too, just as common sense and physics proscribe. For example, certain physical forces interact with a human body which, in turn, acts on the mind and thus causes a red sensation. What Adickes’s interpretation of Kant’s philosophy amounts to is a scientific realism, as described above, which is suspended between two unknowable poles and which involves an unknowable process. The unknowable poles are the Ding an sich and the Ich an sich. The unknowable process is the creation of the physical world and the empirical self.

What a strange and fascinating view! I have no doubt whatsoever that it is just as false as the view usually ascribed to Kant. But I think that it would be a mistake to dismiss Adickes’s interpretation for this reason alone. Quite to the contrary, I think that he catches an important undercurrent in Kant’s philosophy. Kant, I believe, was indeed under the spell of “scientific realism” and quite often allowed this spell to dictate his choice of example and terminology. So-called scientific realism, and this is the point I wish to make, was and still is a pervasive dogma, a dogma which has had everyone under its spell. Even though Kant’s philosophical arguments led into quite a different direction, he could not but heed its force. Ever so often in Kant’s philosophy, the physical object appears suddenly on the scene, like a ghost that will not be laid to rest. Kant could not rid his philosophy of this ghost. Adickes cannot believe that a philosophy deserves our respect, unless it embraces the dogma.

But the dogma is false. It is false not because it insists, against the idealist, that there are physical objects, but because it denies that the perceptual objects around us are nonmental. It puts the sweet, red, round apple in the mind. And it does so because it takes for granted that these qualities are nothing but sensations in minds. The truth is, though, that the sweetness of the apple, its color, its smell, are just as much part of the objective (nonmental) world as are the molecules of which the apple consists. As Whitehead puts it, “For us, the red glow of the sunset should be as much part of nature as are the molecules and electric waves by which men of science would explain the phenomenon” (A. N. Whitehead, The Concept of Nature, p. 29).

The distinction between primary and secondary qualities serves Adickes’s purpose of inserting a physical object between the Ding an sich and the merely mental perceptual object. True enough, he reasons, the red, sweet, round apple is merely a construction in the mind. But physics tells us in undeniable terms that “out there,” in addition, certain other things exist, things which, though they have no color, no taste, etc., are not unknowable Dinge an sich. Adickes remarks at one point that the distinction between primary and secondary qualities “presupposes that there are objects which have only the primary qualities and not the secondary ones, but which in regard to the latter only have certain properties to which (more precisely, to the influence of which) our I answers with its subjective reactions: the secondary qualities” (Adickes, p. 69). But what are those primary qualities? Philosophy once again gets in the way of physics: “If one thinks about the distinction between primary and secondary qualities more thoroughly, then one must conclude that everything that constitutes matterness, that is, the occupation of space by matter . . ., stands or falls with the secondary properties. What remains are forces . . . Really free from secondary qualities one becomes if and only if one traces back the occupation of space to an interaction of forces” (Adickes, p. 71). The physical objects saved from Berkeleyan idealism, in the end, thus turn out to be philosophical chimeras, not the esoteric particles of modern physics. Adickes’s attempt to reconcile Kant with physics is a case of love’s labor lost. There is an important lesson in all of this for us. The philosophical arguments for the distinction between primary and secondary qualities lead, not to scientific realism, but to a philosophical realism according to which the things “out there” are neither the familiar perceptual objects around us nor the strange physical objects of the physicist’s theory.