Why Problematic Idealism is Not a Problem Kant's Refutation of Idealism as a Response to Hume's Skepticism

Charles W. Johnson
1 May 2002

This present essay is © 2002 by Charles Johnson, and is available for reproduction and derivative works under the terms of the Creative Commons Attribution-ShareAlike 2.0 copyleft license. If you have any questions or comments about the essay, feel free to contact the author.


Before me I see a table. Beneath me, I feel a chair supporting me. And from another room, I hear people talking. I live within and interact with a world of objects that I touch, see, hear, smell, and taste. Furthermore, there are times in which I do not see, feel, or hear these things. I blink. I stand up for a moment. I shut the door and drown out the noise. And there are ever so many objects which I could not directly perceive at all, because they are out of the range of my senses--my car, for example, is in C-zone (far beyond the horizon of any possible perception), and particular books sit on the shelves of the Auburn University library. I constantly act on the presumption that these objects, which I do not perceive, nevertheless exist. I sit back down without looking down to see if my chair remains. I hike across the arid expanse between here and C-zone to get to my car and drive home at the end of the day. I take it for granted that objects exist outside of me in a certain way, such that they remain even when I am not aware of them. (1.1)


Yet such a mundane and indubitable experience may still provoke the puzzled raise of the eyebrow which Plato assures us is the quintessential tic of philosophy. After all, where in the world do I get the certainty that this table before me persists when I have no sights or sounds or feelings to tell me that it does? And why should I hold that what it is for my car to be in C-zone is anything other than my seeing it in C-zone--what other mode of being could I even be in a position to talk about? I seem awfully sure of things of which I don't, prima facie, seem to have a lot of evidence, and with the situation muddied as it is, philosophical reflection is perhaps in order. (2.1)

In Section I.IV.ii of A Treatise of Human Nature, entitled Of scepticism with regard to the senses, David Hume turns his critical attention to our commonsense belief in a persistent world of objects. The inquiry, he observes, can be divided into two component questions of Why we attribute a continu'd existence to objects, even when they are not present to the senses (188), and why we suppose them to have an existence distinct from the mind and perception (188). With regard to each question, he then asks the only questions, that are intelligible on the present subject (188), which is to examine the possible sources of each belief to consider, whether it be the senses, reason, or imagination, that produces the opinion (188). Since we no sooner establish the one than the other follows, as a necessary consequence (210), we can vindicate our commonsense beliefs either by finding a way in which the belief in continued, or in distinct, existence of objects comes to us through the use of the senses or reason. If, on the other hand, we could only come to these beliefs by way of imagination, then it can only be a product of custom and imagination, and cannot be a rational grounds for knowledge or action. (2.2)


The question of continued existence of objects arises specifically because our sensible awareness of objects is interrupted. So long as I look at the table in front of me, I can see that it continues to exist. But should I close my eyes, or turn my head, I no longer see it at all--let alone seeing it continue to exist. And there are ever so many things which are not in my field of awareness at any given time; the world is a great deal bigger than the part of it that I can perceive. The very structure of the question is such that it is a contradiction in terms to claim that the senses can ground the belief in a continued existence of objects, since the move supposes that the senses continue to operate, even after they have ceas'd all manner of operation (188). We cannot sense that which we are not sensing, and thus the senses fail to confer to us the idea of a continued existence. (3.1)

Nor can we argue that the senses present themselves to the mind as representations of objects distinct from our perceptions. In order to do so, the senses would have to present to us the idea of both an image and the object which it represents. To Hume, however, it is clear that sensations convey to us nothing but a single perception (189), which is nothing more than the sensation itself. A single perception can never produce the idea of a double existence (189) without stepping from the realm of pure sensation to that of inference. It would be inconceivable for the senses to give us an impression of their objects distinct, since this would require the senses to present themselves, by a kind of fallacy and illusion (189), as something other than sensations. Even if they could do such a thing, it would give us no warrant for the belief in external objects, and in any case, Hume argues, all actions and sensations of the mind are known to us by consciousness [and] necessarily appear in every particular what they are (190). Their esse is percipi, and for them to deceive us in such a way would be for them to lose the very nature of their existence. (3.2)


Perhaps, then, we might be able to argue our way to a persistent world, to come to the opinion by way of reason. Indeed, many early modern philosophers advanced arguments for the existence of corporeal substance. Hume, however, expeditiously disposes of all such arguments on the grounds that 'tis obvious these arguments are known but to very few, and that 'tis not by them, that children, peasants, and the greatest part of mankind are induc'd to attribute objects to some impressions (193). In everyday life, even the most sophisticated metaphysician has an instantaneous and powerful belief in continuing existence, which she maintains without ever consulting reason, or weighing [her] opinions by any philosophical principles (193). We must find some explanation for the belief in external objects other than the metaphysical speculations of a few, and once we have such an explanation, it seems that searching after arguments will simply be superfluous. (4.1)

Moreover, the arguments of the philosophers have generally sought to show that the impressions of the senses are effects, of which continued and distinct objects are posited as reliable causes. Hume's notorious objections to causal reasoning to one side, we can also simply point out that such a schema can never work when applied to the relationship between perceptions and objects, unless we find some independent means by which we come to conceive of objects distinct from our perceptions. For unless we already have a means by which we come to be aware of objects distinct from our perceptions, we can never observe [a conjunction] between perceptions and objects (212). So long as half of the equation is completely missing from our experience, we can never even formulate what it would mean for the causal relationship to obtain, let alone reason rightly whether it does or not.(4.2)


If our belief in continued distinct existences arises neither from the senses, nor from either deductive or causal reasoning, then the only principle capable of explaining all of our beliefs in continued existence is association in the imagination. The association is not a causal reasoning from constant conjunction, but rather one of mistaken identity. When we have been accustom'd to observe a constancy in certain impressions, Hume observes, their resemblance can lead us to mistakenly fail to regard these interrupted perceptions as different, (which they really are) but on the contrary consider them as individually the same, upon account of their resemblance (199). The appearance of a completely resembling perception causes the imagination to pass to the memory of the earlier perception, causing us to misidentify the first perception with the second, and determining for us the notion of a continued existence of our impressions. (5.1)

Yet as was earlier observed, the very nature of the senses is that they are interrupted, and I am intimately aware of this fact. It is the conflict between the determinations of the imagination, on the one hand, and my intimate awareness of the fleeting nature of the senses, on the other, which structures the question of external objects. Since this interruption of [the impressions'] existence is contrary to their perfect identity (199), I am caught on the horns of a dilemma, and reason demands that I must look for relief by sacrificing the one or the other (206). Either I must abandon the identification of the impressions by my imagination, or else I must suppose that my senses deceive me. (5.2)

I am so powerfully convinced of both opinions, however that I cannot give up either my imagination or my senses. Out of the dialectical tension between them arises a system which is the monstrous offspring of two principles, which are contrary to each other, which are both at once embrac'd by the mind, and which are unable mutually to destroy each other (215). In order to avoid the contradiction in which I am caught, imagination supposes that these interrupted perceptions are connected by a real existence, of which we are insensible (199). Thus I form a belief in a distinct existence in order to recuperate the contradiction between the inconstancy of my perceptions, and my indestructible belief in continued existence. (5.3)


However, upon philosophical reflection, I find that I cannot maintain this belief while also presuming that I directly perceive objects in the world. If my perceptions were the same as the objects themselves, then how could I claim that those objects are distinct from my mind? In order to remove this contradiction, I employ a sharp distinction between the appearance of a perception in the mind and its existence (206). For my belief in distinct existence to work, I must give up the naive realist opinion that the image I see before me is the chair itself. It is, rather, the appearance presented to my mind of a distinct thing, the chair. The chair itself is what connects and explains the various interrupted impressions I have of the chair. (6.1)


But, as Hume argued above, this double existence can never be supported. If I never can have an impression of any distinct objects, and I have no ideas that are not copies of impressions, then I can never form a clear idea of objects as any thing but exactly the same with perceptions (218). Philosophers who posit a double existence, therefore, only deny our resembling perceptions to be identically the same, and uninterrupted; and yet … arbitrarily invent a new set of perceptions, to which they attribute these qualities (218, emphasis added). (7.1)

But these supposed objects are ultimately unintelligible, since the philosopher has merely posited a set of imperceptible perceptions, and What then can we look for from this confusion of groundless and extraordinary opinions but error and falshood? And how can we justify to ourselves any belief we repose in them? (218). Not only can we not justify our belief in external objects as distinct from perceptions, but, in fact, that belief is by nature incoherent. From the standpoint of rigorous examination in light of reason, my beliefs about the external world are at odds with the method of any sound philosophy. (7.2)


Yet I need these beliefs in order to act in any sort of coherent fashion with the outside world. Though I may not know that my car remains while I leave it in the parking lot, I must assume that it does if I am to drive to and from my classes. In order to avoid being reduced to philosophical melancholy and delirium (269), I must believe that an impression is somehow something real and durable, and … preserving its existence (197); yet this belief cannot stand up against any critical examination. Hume advises that the only solution is the judicious application of Carelessness and in-attention (218) to this area of our belief. There is an inescapable tension between two convictions of our mind, and as we cannot reject either, our only hope is to complacently resign ourselves to examining neither. (8.1)


As with many issues raised in Hume's philosophy, Kant addresses this question in his Critique of Pure Reason, with his most focused attack found in the Refutation of Idealism in Chapter II of the B-edition Transcendental Analytic. The specific point of attack is Hume's reflection on the nature of perceptions, in a premise of Hume's which Kant describes as problematic idealism, the doctrine that the only immediate experience is inner experience, and that from it we can only infer outer things--and this, moreover, only in an untrustworthy manner (B276). (9.1)


The only existences, of which we are certain, are perceptions, which being immediately present to us by consciousness, command our strongest assent, and are the first foundation of all our conclusions (Hume 212). These words, it seems to Kant, give us a particular picture of the essence of human experience. We are, first and most intimately, aware of our own thoughts, desires, sights, sounds, feelings. Through the mediation of these objects of inner sense we infer (rightly or wrongly) outer objects, which continue to exist even though our ideas and impressions are interrupted, and which exist distinctly from those impressions and ideas that we have of them. (10.1)


My impressions progress in time. Now I am aware of the table, now the floor, now I attend to the sound of my own voice, and now I remember that I left my car unlocked. My perceptions are determined in time, one after the other. But to determine thoughts in time, there must be some permanent upon which thought in general is predicated, as under Kant's First Analogy, All determination of time presupposes something permanent in perception (B275). If I am to be aware of my impressions and ideas one after the other, there must be a substance of which I am aware, which is the grounding for the various thoughts. (11.1)

The substance, I may immediately answer, is nothing more than the self or spirit which holds all the ideas. The mental phenomena which I have are the accidents of a spiritual substance. But what here do I mean by the self or spirit? Kant argues that if the self is taken in the sense of the transcendental thinking I, then The consciousness of myself in the representation I is not an intuition, but a merely intellectual representation of the spontaneity of a thinking subject (B278), and will not suffice for the demands of the First Analogy. The thinking self is nothing more than a purely formal placeholder, which has not, therefore, the least predicate of intuition, which, as permanent, might serve as correlate for the determination of time in inner sense (B278). It cannot be the permanent by which thought is determined in time, since it has no content apart from the thoughts that it has. And if I take the self as the bundle of mental phenomena of which I am aware, it still cannot serve as the permanent, since those thoughts are precisely the objects that are being determined in time in the first place. (11.2)


The permanent substance of which my thoughts are predicated, then, is not anything within the subject, and Thus perception of this permanent is possible only through a thing outside me (B275). The awareness of this external thing, moreover, cannot be the mere representation of a thing outside me (B275), since a representation without an object is simply another thought within the subject, and it is only through this permanent that my existence in time can itself be determined (B275). The permanent upon which inner sense is predicated must be a real thing outside of the subject, of which it is aware prior to any inner awareness. Thus the determination of my existence in time is possible only through the existence of actual things which I perceive outside me (B275-276). Problematic idealism must be rejected on the grounds that we can be aware of our own thoughts only if we are first aware of something outside of those thoughts. (12.1)


Kant refers the doctrine of problematic idealism to the philosophy of Descartes, but it is clear that he also has Hume's skepticism in mind when he contends that problematic idealism raises … what is a serious objection (B274) which would reduce our guessing or enquiring into the existence of anything [to] an idle pretence (B274). For while Descartes believed he had salvaged the outer world through the mechanism of God's benevolence, it is Humean skepticism that demands agnosticism, and declares the existence of objects in space outside us … to be merely doubtful and indemonstrable (Kant B274). The engagement with Descartes in the Refutation of Idealism, may be seen as an engagement with Hume, where the mention of Descartes serves as a reminder that the source of the error is Hume's Cartesian premise. In this manner, Kant radically rejects the grounds for Cartesian angst, and thus for Humean agnosticism; he argues in such a way that the game played by idealism has been turned against itself, and with greater justice (B276). (13.1)


Consider the picture of human experience we had before. Idealism assumed that the only immediate experience is inner experience, and that from it we can only infer outer things (Kant B276). I have an image of a computer before me, and from this I suppose that there is a thing distinct from me. It is only through the presentation of images that I come to posit things beyond myself. Yet through the argument of the Refutation, Kant seeks to demonstrate that even our inner experience, which for Descartes -- and Hume -- is indubitable, is possible only on the assumption of outer experience (B275). I see a computer, and it is only through seeing a computer that I can have an inner sense of my seeing of the computer. Here outer experience is really immediate, and that only by means of it is inner experience … possible (Kant B276, emphasis added). (14.1)

In order for us to have any awareness of our thoughts we first must think of something else; that something else cannot be anything within the subject, and therefore must be some external thing of which we may truly say cogito. As a result, we must reject Hume's claim that the objects of our outer sense might be produc'd by the creative power of the mind and that their ultimate cause is … perfectly inexplicable by human reason (Hume 84). The existence of things (or at least, one thing) beyond the self is a necessary condition for any awareness of thoughts at all. (14.2)

Hume's problem of how the senses can convey a double existence is now redirected. Since what we are aware of through the senses is not an impression, but rather a thing, the question of double existence now becomes the question of reflective psychology: how is it that in my awareness of a thing I can also be aware of that awareness? It seems to me, however, that we are in a far better position. Developing a doctrine of the faculty of inner sense seems to me to be far more promising of a project than figuring out how one is to use reason to stumble through the veil of Humean impressions into the light of the outer world. (14.3)


Kant's Refutation of Idealism provides a strong rebuttal not just to Hume's ultimate skepticism towards external objects, but towards the fundamental premises which underlie it and enable it. Nevertheless, we have left certain possibilities open, and a devout skeptic will not be satisfied. For example, I may be immediately aware only of my own physical existence as an object in the world, and yet be completely surrounded by hallucinations. Indeed, this seems to be the only way that we can make sense of the situation in which I am a brain in a vat, inhabiting the dream world of a mad scientist's devising. Such a situation may indeed satisfy the perverse epistemological schadenfreude of the skeptic. (15.1)

But here the question has lost the bite that it once had. For whether I perceive the world rightly is certainly an important question, but it is purely an empirical question, to be addressed by the sciences. It is not a transcendental question for philosophy. It does not call into doubt, as Hume's thoroughgoing agnosticism does, that the mind confers to us a world; it only raises the empirical question of whether I rightly perceive the world that must exist. (15.2)


  1. Hume, David. A Treatise of Human Nature. Ed. P.H. Nidditch and L.A. Selby-Bigge. New York: Oxford University Press, 1978.
  2. Kant, Immanuel. Critique of Pure Reason. Trans. Norman Kemp Smith. USA: Macmillan & Co., Ltd., 1965.