Non-Duality and the Problems of Western Idealism – Part 2: Berkeley and Kant

In my previous post I discussed Eastern non-dual spirituality and how it focuses on the Enlightenment experience of non-dual consciousness as the way to Liberation. I explained in particular how the key to non-dual consciousness lies in recognizing that one’s individual person is part of the object side of experience (together with the ‘outside’ world) and that therefore the individual person cannot be the true subject of experience – this true subject being rather non-individual consciousness free from the subject-object duality of individual and outside world. The immediate intuition of this non-dual, non-individual consciousness is what the Enlightenment experience in Eastern spirituality is all about. In this post I will turn to the topic of Western Idealism. Despite all the similarities with Eastern spirituality concerning the fundamental status of consciousness, the Enlightenment experience of the non-individual nature of non-dual consciousness is conspicuously lacking in Idealist philosophers from the West. The theoretical lesson to be learned from the Enlightenment experience is therefore also lacking in Western forms of Idealism. Although Western Idealists acknowledge the fundamental status of consciousness, they keep falling back – mostly as a matter of habit – into the familiar model of individual consciousness with its subject-object duality of individual and outside world. Hence, the question of the “external reality” outside of consciousness kept reasserting itself for Western Idealist thinkers, simply because of their unfamiliarity with anything like the Eastern Enlightenment experience of non-individual consciousness. In this post I will show how this problem emerged for the first Idealist thinkers in the West, namely Berkeley and especially Kant, who exerted the most influence on later Idealism. In a later post I will do the same for Kant’s successor in German Idealism, Fichte.  

The turn to subjective consciousness in early modern philosophy
To understand why Western Idealism never really broke free from the paradigm of individual, subjective consciousness, we have to take into account the history of Idealism in Western philosophy. We must see how it emerged from the epistemological turn to subjective consciousness in the 17th century. With this “New Way of Ideas” (as John Locke called it), philosophers started to focus on individual consciousness as the epistemological foundation of all knowledge, including knowledge about the “external world” outside the individual. This is, however, quite a complex story which we cannot fully narrate here; that would take us too far afield (for the full story, see here and here). In the following, therefore, I will give a short summary of the epistemological turn to subjective consciousness in early modern philosophy and how this gave rise to Idealism in Berkeley and Kant.

The turn to subjective consciousness – taking place with thinkers such as Descartes, Locke, Berkeley and Hume – was occasioned by two main cultural forces: (1) the generally felt desire for certain knowledge and the Cartesian solution of the self-evidence of subjective self-consciousness (“cogito ergo sum”), and (2) the rise of atomism in physical science and the subsequent realization that sensible qualities such as color, sound and smell cannot be objective properties of ‘external’ physical objects but must be merely subjective phenomena in individual consciousness.

These two developments conspired to lock the individual knower up inside the confines of his subjective consciousness, cutting him off from the outside world. Descartes’s cogito argument seemed to show that certainty can only be found within consciousness, whereas the other development – the scientific insight that sensible qualities are not objective properties – led to the idea that we never experience anything outside of our own consciousness anyway. The general picture that thus arose was of the knowing subject as ‘imprisoned’ inside his “circle of consciousness”, with physical objects impinging on it from the outside, causing subjective perceptions within the circle. As the Cartesian philosopher Antoine Arnauld summarized the situation: “We have no knowledge of what is outside us except by mediation of the ideas within us.” (Arnauld 1964 [1662]: 31)

The Way of Ideas and the problem of skepticism
Although the epistemological turn to subjective consciousness in 17th century philosophy was motivated by the desire for certain and scientific knowledge, the irony of the situation was that it produced a radical skepticism that seemed to undermine science (a skepticism that became rampant with Hume’s attack on causality). For if certainty pertains only to what is inside consciousness, how then can we know what is outside, the external reality? If all we know with certainty are the contents of consciousness, how then can we know whether these contents correspond to external objects? After all, as the problem was frequently put, we cannot step outside our consciousness in order to inspect its correspondence, or lack thereof, with the outside world. Thus, the very medium that should give us cognitive access to external reality – namely, sensory experience – became a “veil-of-perception” hiding reality. As Barry Stroud put the problem in his classic work on skepticism, summarizing the upshot of the New Way of Ideas: “We are restricted to the passing show on the veil of perception, with no possibility of extending our knowledge to the world beyond. We are confined to appearances we can never know to match or deviate from the imperceptible reality that is forever denied to us.” (Stroud 1984: 33-4)

Berkeley and Kant: Idealism as solution to skepticism
It was in response to this skeptical threat that modern Idealism emerged in Berkeley and Kant. As both of them pointed out, the skepticism invited by the epistemological turn to subjective consciousness was premised on the assumption of a reality external to consciousness; simply strike that assumption, they argued, and the threat of skepticism vanishes. If reality is ‘just’ a product of the mind, then surely its knowability can pose no problem? Berkeley and Kant, then, attempted to solve the problem of skepticism by cutting the Gordian knot: there is no “external world” outside of consciousness, the only world to be known is the phenomenal world appearing in consciousness.

Thus Berkeley saw himself as restoring common sense when he expounded this Idealist principle that “to be is to be perceived” (“esse is percipi”). In his view, the Way of Ideas had violated common sense by seeing the object of sense experience as something radically different from the sensible qualities appearing in experience: “Upon the common principles of philosophers, we are not assured of the existence of things from their being perceived. And we are taught to distinguish their real nature from that which falls under our sense. Hence arises Scepticism and Paradoxes.” (Berkeley 1969 [1713]: 3) His principle that “to be is to be perceived” allowed him to say that the object of sense experience simply is the bundle of sensible qualities experienced, and nothing beyond that. Thus he could restore the common-sense belief that when we eat a cherry, and see its redness, taste its sweetness, etc., we are perceiving the cherry itself, not just its appearance as distinct from the real thing: “I see this cherry, I feel it, I taste it […]: it is therefore real. Take away the sensations of softness, moisture, redness, tartness, and you take away the cherry.” (Berkeley 1969 [1713]: 117)

In a similar manner Kant dealt with Hume’s skeptical attack on causality. Hume had undermined the notion of causality – which is so crucial for physical science – by pointing out that we only experience the sense impressions caused by external objects, not those objects themselves. Thus, we only observe the regular connections between the sense impressions, but this gives us no certainty about the nature or even the existence of causal relations between the external objects. As Hume said: “Thus not only our reason fails us in the discovery of the ultimate connection of causes and effects, but even after experience has informed us of their constant conjunction, ‘tis impossible for us to satisfy ourselves by our reason, why we should extend that experience beyond those particular instances, which have fallen under our observation.” (Hume 2003 [1739-40]: 66)

Kant was deeply disturbed by Hume’s attack on causality. His respect for the physical science developed by Copernicus, Galileo and Newton was so great that he simply could not stomach Hume’s dismissal of causal laws. Where Hume went wrong, according to Kant, was in his assumption that causality, if it exists at all, must be a feature of external reality, in other words, that causal connections must be connections between real objects, independent of our consciousness. But, as Kant argued, such external objects are “nothing to us”. Objects become something for us, i.e. they become accessible to us as experienceable and knowable objects, only if they conform to our forms of cognition, and causality is one such form. Raw sensations do not yet give us experiences of objects. The sensations have to be ordered by our forms of sensory intuition (space and time) and our forms of conceptual understanding (the categories, prime among which is causality); only then do we experience a single, ordered, integrated reality consisting of interconnected objects. Hence Kant’s Idealism: the world to be known by us is not an “external world” outside of consciousness, but a construction within consciousness, an ordering of sensory material by means of cognitive forms such as time, space and causality.

Kant’s Transcendental Idealism
I will say a bit more about Kant’s Idealism, because it was – much more than Berkeley’s – a crucial influence on subsequent Idealistic thinking, and also because the persistence of the paradigm of individual consciousness becomes especially clear in Kant. The first thing to note here is that Kant’s Idealism extends only to the forms of empirical reality, not to the sensory material structured by these forms. This is why Kant calls his philosophy “transcendental Idealism”, the term “transcendental” being his technical term for what pertains to the a priori forms of cognition: “I call all cognition transcendental that is occupied not so much with objects but rather with our a priori concepts of objects in general.” (CPR, A12) In extension, Kant speaks of the “transcendental subject” as the subject who applies the a priori forms of cognition to the sensory material.

Ultimately, the necessity of the sensory objects to conform to our forms of cognition has to do with the fundamental role Kant accords to self-consciousness in experience and knowledge. According to Kant, a process or state in my consciousness counts as an experience or belief only if I can be aware of it as my experience or my belief, thus only if it belongs to the unity of my consciousness – a consciousness that forms a unity precisely because it is mine, i.e. because all episodes and states in it are related to me as their underlying subject. For a mental episode or state to be mine, then, I must as it were be able to prefix it with the qualifier “I think…”. By prefixing “I think…” (or “I see…”, “I hear….” etc.) to a mental content, I indicate that the content belongs to the unity of my consciousness. As Kant puts it:

“The I think must be able to accompany all my representations; for otherwise something would be represented in me that could not be thought at all, which is as much to say that the representation would either be impossible or else at least would be nothing for me… The thought that these representations […] all together belong to me means, accordingly, the same as that I unite them in a self-consciousness […].” (CPR: B132, B134)

According to Kant, the ultimate function of the forms of space and time and the categories of the understanding is to effectuate this unity of self-consciousness (a unity that Kant therefore calls “transcendental”, since it underlies the application of the a priori forms of cognition). Only by placing all my mental episodes and states within a unified spatiotemporal network of causal relations can I recognize those episodes and states as mine, as belonging to my (self-)consciousness. The resulting integrated unity of empirical reality, then, is for Kant only a reflection or projection of the transcendental unity of self-consciousness unto the unorganized manifold of raw impressions. The unity of the object, and thereby the object as such (because there is no object without unity), is really a manifestation of the unity of the subject’s self-consciousness.

The paradigm of individual consciousness in Berkeley and Kant
To repeat: Berkeley and Kant attempted to solve the problem of skepticism posed by the epistemological turn to consciousness by simply striking the assumption of a world outside of consciousness; hence their Idealism. This is, however, only one side of their story, for the jettisoned assumption of a reality outside of consciousness came right back through the back door of their systems, in the form of God for Berkeley and the thing-in-itself for Kant. Here we begin to see how Western Idealism never really broke free from the paradigm of individual consciousness and how this paradigm kept dictating the theoretical problems that Idealist thinkers were supposed to solve.

Even if Berkeley and Kant argued that “objective reality” – reality as the object of sensory experience and rational knowledge – exists only as a phenomenon within consciousness, they still felt they had to posit a cause for that phenomenon outside of consciousness: God for Berkeley, the thing-in-itself for Kant. Why? Well, so they reasoned, sensory objects do exist only within our consciousness, but we nevertheless have no awareness of having produced them; their appearance within consciousness is independent of our will, in contrast to those mental states that we can freely create ourselves (such as thoughts and fantasies). Thus, although sensory objects exist only within consciousness, they must nevertheless have a cause outside of our consciousness.

In this vein, Berkeley admits that humans have perceptions “whereof they themselves [are] not the authors, as not being excited from within, nor depending on the operations of their will” – perceptions, then, that have an external cause. But since, according to Berkely, all being is being perceived, the being of that cause must be relative to a perceiving consciousness outside of us, another mind that installs those involuntary perceptions within our minds – and for Berkely this can only be the mind of God, “the supreme spirit which excites those ideas in our minds” (Berkeley 1995 [1710]: 44-45). 

Kant reasoned much in the same way, though he ended up by invoking an unknowable “thing-in-itself” rather than God as the cause of the sensory material appearing in consciousness. Kant agreed with Berkeley that although Idealism avoids skepticism by placing “objective reality” within consciousness, it still needs to explain the external origin of the sensory material out of which “objective reality” is created. As said, according to Kant, the sensory material becomes an experienceable and knowable object for us only when it is ordered by our a priori forms of cognition (space, time, causality). With respect to those forms, then, we are active, “spontaneous” as Kant put it, meaning that we freely impose the forms on the sensory material. But with respect to the sensory material itself, we are passive, “receptive”, meaning that the sensory material arises in consciousness because we are “affected” from the outside. Here Kant agreed with Berkeley that human beings experience sensations “whereof they themselves [are] not the authors, as not being excited from within, nor depending on the operations of their will” (Berkeley 1995 [1710]: 44). Hence the well-known dichotomies drawn by Kant between spontaneity and receptivity, a priori and a posteriori, cognitieve form and sensory material, etc. It is to account for the alleged passive, receptive side to our consciousness that Kant felt necessitated to invoke something outside of consciousness, the thing-in-itself, as the cause of the sensory material appearing within consciousness. It was only in line with his Idealism when he then declared this thing-in-itself to be completely unknowable to us, given that the only reality we can know – according to Kant – is the phenomenal reality constructed in consciousness.

Kant on “inner” and “outer sense”
As I said above, it is here that we start to see how Western Idealism never really broke free from the standpoint of individual consciousness, thereby creating insoluble problems for itself. The point is that the sensory passivity of consciousness holds only for individual consciousness, i.e. for the individual subject who stands over against his object, the external world. Thus, the sensory passivity of consciousness still presupposes the subject-object duality. But hasn’t this duality been overcome once consciousness is recognized as the condition for the appearance of both subject and object, in the sense of the individual and his world? And doesn’t it then follow that this consciousness, that precedes the appearance of subject-object duality, is itself free from subject-object duality and is thus “non-dual”, as Eastern spirituality says? But if this is so, if consciousness is prior to the subject-object duality, why then attribute receptivity to consciousness when the very idea of receptivity clearly presupposes this duality? The lingering attachment of Western Idealists to the idea that there is a receptive side to consciousness is a clear category mistake, a confusion of the transcendental consciousness with the individual consciousness (which is better called the “individual mind”) which is just one of the appearances within transcendental consciousness.

It seems to me that this category mistake emerges clearly in Kant when he introduces the distinction between “inner” and “outer sense” into his Transcendental Idealism. This distinction is really Kant’s acknowledgment that the subject-object duality is merely an appearance within transcendental consciousness. For Kant, “inner sense” designates the psychological self-experience of the individual person, the sensing of individual mental states such as thoughts and feelings. It is through inner sense that the individual mind (“Gemüth”) “intuits itself or its inner state” (CPR, A23/B37). Correlatively, “outer sense” is for Kant the sense through which the individual mind senses the outside world; with the outer sense “we represent to ourselves objects as outside us” (CPR, A22/B37). Now, the crucial move on Kant’s part here is his recognition that transcendental consciousness is prior to both inner and outer sense: not only the objects appearing in the outer sense but also the objects appearing in the inner sense are just phenomena constructed by consciousness. Thus, Kant stresses emphatically that the psychological self-experience of inner sense is certainly not to be confused with the transcendental self-consciousness underlying all experience, the unity of the “I think” that unifies all what appears in consciousness (CPR, B153).

Kant’s category mistake: the receptivity of the transcendental subject
It follows that the transcendental subject, the I that holds together all phenomena in the unity of its self-consciousness, is not the individual self whose mind is experienced through inner sense and whose sensory affection by an external world is experienced through outer sense. But if this is so, why then does Kant attribute this sensory affection – this “receptivity” – to the transcendental subject? Clearly, Kant commits a category mistake here. The only evidence we have for the existence of receptivity comes from the phenomenal realm, from the dichotomy of inner and outer sense, thus from the experience of the individual person as limited and affected by his external world. So by attributing receptivity to the transcendental subject, Kant is confusing the phenomenal and the transcendental: he is attributing a phenomenal property (receptivity) to the transcendental precondition of all phenomenality, the transcendental subject.

In his own terminology, Kant is guilty here of an “amphiboly”, which is his term for the mistake he detected in his empiricist and rationalist predecessors, namely the confusion of the a priori and a posteriori. According to Kant, rationalist philosophers tended to mistake a posteriori givens with a priori products of the mind; here Kant targeted above all Leibniz with his extreme claim that all concepts are “innate”. Conversely, empiricist philosophers tended to make the opposite mistake of seeing the a priori as a sensory given; here Kant targeted philosophers like Locke who saw all concepts, including a priori concepts such as causality, as deriving wholly from sensory experience.

For Kant, seeing the truth in epistemology hinged on avoiding such “amphibolies”, thus on distinguishing clearly between a priori and a posteriori and on assigning each its proper role in cognition. In this way, Kant aimed to steer a middle course between empiricism and rationalism by recognizing both the spontaneous and the receptive side of consciousness. But isn’t it clear now that Kant’s own middle course is itself predicated on an amphiboly, and indeed a rationalist amphiboly, such that an a posteriori given (the receptivity of cognition) is mistaken for an a priori insight in the nature of transcendental consciousness? This is what Kant’s account of the distinction between inner and outer sense makes clear, namely that the duality of subject and external object – and thus the sensory affection of the former by the latter – is a phenomenon appearing in transcendental consciousness and therefore not a property of this consciousness which pre-conditions all phenomenality.

In this sense, Kant’s recognition of the phenomenal nature of the inner sense / outer sense duality should have clearly shown to him the non-dual nature of transcendental consciousness itself. That is, it should have made it perfectly clear to him that the transcendental subject, whose self-consciousness unifies all phenomena, is a non-dual subject, i.e. a subject without an external object (“one without a second” in the language of the Upanishads). The fact that Kant didn’t see this, that he continued to attribute – amphibologically – the phenomenal property of receptivity to the pre-phenomenal transcendental subject, testifies to the strong hold that the paradigm of individual consciousness exerted on Idealist philosophers in the West.                      
 
References
-Arnauld, A. (1964 [1662]), The Art of Thinking. Indianapolis: Bobbs-Merrill.
-Berkeley, G. (1995 [1710]), A Treatise Concerning the Principles of Human Knowledge. Indianapolis: Hackett Publishing.
-Berkeley, G. (1969 [1713]), Three Dialogues Between Hylas and Philonous. Chicago: Open Court.
-Hume, D. (2003 [1739-40]), A Treatise of Human Nature. Mineola: Dover Publications.
-Kant, I (1998 [1781-87]), Critique of Pure Reason. Cambridge: Cambridge University Press.
-Stroud, B. (1984), The Significance of Philosophical Scepticism. Oxford: Oxford University Press.

The Problem of Skepticism in Early Modern Philosophy of Consciousness

This post is part of a larger project I am working on: a critique of the epistemologically motivated Idealisms of Berkeley, Kant, and the post-Kantians. I am greatly attracted to Idealism, but I think we should accept it primarily on ontological grounds, i.e. because Idealism gives the best explanation of why reality exists and why it is as it is. Hence my criticism of the Idealisms of Berkeley, Kant, et al., because for them Idealism was primarily epistemologically motivated, Idealism being their solution to the problem of epistemological skepticism as it arose within the early modern philosophy of consciousness advanced by Descartes, Locke, and their followers. As I will argue in a next post, modern Idealism, as an answer to this threat of skepticism, fails miserably (thus the only remaining reasons for accepting Idealism must be ontological). To prepare the way for this critique of epistemological Idealism, this post explains how the problem of skepticism arose in the early modern philosophy of consciousness, or the “Way of Ideas” as it was known to Descartes, Locke and their contemporaries. 

The Way of Ideas
There were two main, interconnected forces driving early modern philosophers towards the Way of Ideas and its epistemological centralization of consciousness. One of these forces was the desire for certain knowledge, which arose from the quarrels between the Church and the new natural science of Copernicus and Galileo, which rose all kinds of thorny issues concerning the authority of Faith and the powers of Reason. Here, famously, Descartes used the cogito ergo sum argument as a way to ground the certainty of knowledge on the self-evidence of consciousness’ knowledge of itself. Thus, the range of certain knowledge became limited to individual consciousness and its ‘contents’ (generically called “ideas” or “representations”; Kant spoke of “Vorstellungen”). According to the proponents of the Way of Ideas, then, the subject knows primarily what is inside the “circle” of his consciousness; only those contents are immediately present to it. All things outside consciousness are known mediately, by conjecture on the basis of what is inside consciousness (sensations, feelings, concepts, thoughts).

The other force that drove early modern philosophers to embrace the Way of Ideas was the atomism – or “corpuscular philosophy” – of the new natural science. Reviving (and transforming) the atomism of Democritus, the proponents of the new science advanced the hypothesis that all natural phenomena are explainable in terms of tiny particles of matter, “corpuscles”, interacting mechanically in space. This, however, led to the question of how to explain sensory qualities such as colour, smell, sound, and taste, which are notoriously subjective. What colour something appears to have or how it sounds, tastes or smells can differ from person to person, depending on one’s physical constitution and the surrounding environment (thus, a thing’s colour changes with the light falling on it; things can taste and smell differently when you are sick, etc.). However, like the atoms of Democritus, the corpuscles of the new science were supposed to exist objectively, independently of our consciousness of them. They were, moreover, supposed to be so small as to be imperceptible and thus as being in themselves without colour, taste, smell, etc. Hence, like Democritus, the corpuscularians – including Descartes and Locke – concluded that such sensory qualities were merely the effects in our minds of the collisions of corpuscles on our sense organs. Such sensory qualities, then, are only subjective and do not reveal the objective qualities of the corpuscles, which consist merely of solidity, spatial form and position, and motion. This distinction between subjective and objective qualities became known as the distinction between secondary and primary qualities. Whereas the primary qualities, such as spatial position and motion, are objective, measurable, and mathematizable, and thus are crucial to natural science, the secondary qualities convey no trustworthy information about the reality outside our consciousness.

The general picture that thus arose was of a knowing subject locked inside his “circle of consciousness”, with external objects impinging on it from the outside, causing perceptions within the circle. “We have no knowledge of what is outside us except by mediation of the ideas within us,” as the Cartesian philosopher Arnauld (1964 [1662]: 31) summarized it. Such was the overall conceptual framework within which the Way of Ideas operated. And although this focus on consciousness was partly motivated, notably in Descartes, to provide a secure foundation for knowledge, the irony of the situation was that the Way of Ideas ended up fostering a radical epistemological skepticism. For if certainty pertains only to what is inside consciousness, how then can we know what is outside consciousness, the external reality? If all we know with certainty are the contents of consciousness, how can we know that these contents correspond to external objects? After all, as the problem was frequently put, we cannot step outside our consciousness in order to inspect its correspondence, or lack thereof, with external reality. 

The Veil of Perception and the Cartesian Circle

The problem is sometimes put in terms of a veil-of-perception theory which has been attributed to Descartes, Locke, and other philosophers of the Way of Ideas. On this theory, our sensory experiences of external objects do not give us cognitive access to these objects but rather form a ‘veil’ or ‘screen’ hiding them from our view. So the medium we use to know external objects, our sensations and ideas, blocks our very access to them. Thus Barry Stroud describes Descartes’ sceptical conclusion in his First Meditation as “implying that we are permanently sealed off from a world we can never reach”: “We are restricted to the passing show on the veil of perception, with no possibility of extending our knowledge to the world beyond. We are confined to appearances we can never know to match or deviate from the imperceptible reality that is forever denied to us.” (Stroud 1984: 33-4) Similar veil-of-perception theories have been attributed to Locke, Berkeley and Hume (cf. Bennett 1971).

The radical nature of the epistemological problem created by this veil-of-perception theory is well illustrated by the desperate solution offered to it by Descartes. In his Meditations on First Philosophy he famously argued that the only way to ‘pierce through’ the veil of perception, in order to reach the objects in themselves, is by evoking God, whose goodness would guarantee the veracity of our perceptions, such that “all things which I perceive very clearly and distinctly are true” (Descartes 1996 [1641]: 24). But to this solution, of course, the skeptic can easily respond by asking how Descartes can know for sure that God exists. If our ideas form a screen between us and external reality, then surely they would also screen us from the true nature of God, if He exists at all. Descartes had an answer to this, but few would find it convincing. It could even be argued that it is downright circular. Descartes argued that we find within our minds an idea of an infinite being, thus an idea which we as finite beings cannot possibly have produced; thus, it can only have been put in our minds by our Creator, “like the mark of the workman imprinted on his work” (Descartes 1996 [1641]: 35). Descartes’ assumption, however, that a finite being cannot form any idea of infinity, is rather questionable. Therefore Descartes also had recourse to a version of the ontological proof of God’s existence. But, as was already pointed out by critics in Descartes’ time, this makes his argument for the veracity of clear and distinct ideas rather circular. For Descartes cannot know that this proof of God does not contain any error unless he assumes that his clear and distinct perception of the steps of his reasoning guarantees that the proof is correct. So Descartes has to presuppose the veracity of clear and distinct ideas in order to prove the existence of God, which he then invokes as the guarantee of this very veracity – a conundrum known as the “Cartesian circle”.

The Problem of Primary and Secondary Qualities in Democritus, Locke, and Berkeley
The Way of Ideas, then, fostered epistemological skepticism by imprisoning the knowing subject within the circle of his consciousness, hiding external reality behind a veil of perception. It is often said that this type of skepticism was exclusively modern and cannot be found in premodern times. This is by and large true, but not entirely. It is true that for Pyrrhonism, the dominant form of epistemological skepticism in antiquity, the gap between what is in consciousness and what outside it didn’t matter much (Pyrrhonism was mainly concerned with showing that we can have no definitive criterion of truth, since every proof of such a criterion must either be circular or presuppose another criterion of truth, for which then the same problem arises). Nevertheless, the problem of the gap between consciousness and external reality was not completely unknown in classical philosophy, as shown by the remarkable case of Democritus, the "laughing philosopher". Not only did Democritus, with his atomism, anticipate the modern scientific worldview, he also anticipated the modern distinction between primary and secondary sensory qualities, as well as the epistemological skepticism induced by this distinction. In one of the few surviving fragments of his work, Democritus stages a striking dialogue between the Intellect and the Senses:

“Intellect: By convention there is sweetness, by convention bitterness, by convention colour, in reality only atoms and the void.
 Senses: Foolish intellect! Do you seek to overthrow us, while it is from us that you take your evidence?” 

In other words: if the secondary qualities do not convey objective information about the atoms, how can we ever know about them? How, in particular, can we know their primary qualities, since we cannot experience a thing’s spatial position and motion apart from its colour, sound, etc. If we disregard all secondary qualities, external objects become utterly unobservable to us. This means, as Democritus realized, that the atomic theory undermines the very credibility of the empirical evidence on which it rests. Democritus’ point was later repeated by early modern philosophers, notably Berkeley in his critique of Locke. 

Locke conceded that secondary qualities give us no insight into the true nature of external objects, but like Descartes he remained steadfast that we can nevertheless know these objects by observing their primary qualities, e.g. spatial position and motion. Thus Locke claimed that “the ideas of primary qualities of bodies are resemblances of them, and their patterns do really exist in the bodies themselves, but the ideas produced in us by these secondary qualities have no resemblance to them at all” (Locke 1996 [1689]: 51). Berkeley objected – much as Democritus had argued some 2000 years earlier – that we can observe a thing’s primary qualities only through its secondary qualities, and thus that our beliefs about the primary qualities of external objects are as problematic as the secondary qualities we attribute to them. Thus, Berkeley writes: “In short, extension, figure, and motion, abstracted from all other qualities, are inconceivable. Where therefore the other sensible qualities are, there must these be also, to wit, in the mind and nowhere else.” (Berkeley 2003 [1710]: 35)

Locke and the Problem of the ‘Thing in Itself’
In this way, however, Berkeley only aggravated a skepticism that was already present in the inaugurators of the Way of Ideas. We have already seen how Descartes felt the sceptical challenge and how he attempted to meet it by invoking God as the guarantor of the veracity of his “clear and distinct ideas”. Locke, too, felt this challenge. Although Locke thought (pace Berkeley) that we can know an external thing’s primary qualities, he also thought that we could not know what that thing is in itself, independent from its relation to us and other objects. Primary qualities, after all, are thoroughly relational, pertaining to a thing’s position in space and motion relative to other things. But what is an external thing in itself, apart from those relations? This, as Locke conceded, we cannot know, since we are ‘locked’ (pun unintended) inside our consciousness and cannot inspect objects as they exist outside of consciousness. Thus, what a thing is in itself, what the Aristotelians called its “substance”, was for Locke merely a “supposed” something “I know not what” (Locke 1996 [1689]: 123). For Locke, therefore, even the new natural science, despite its huge empirical success in the work of Galileo and Newton, yielded only opinion, not knowledge. Such sceptical modesty concerning the success of the new physics was in fact widely shared in early modernity, even by those who were directly involved in the development of the new science, such as Mersenne and Gassendi in France and John Wilkins in England. For all of them, our ‘imprisonment’ in consciousness precluded any knowledge about the true nature of external reality. 

Hume’s Critique of Causality
The authority of epistemological skepticism was further cemented by David Hume, who specifically undermined the causal claims of natural science, i.e. the claim that the scientist’s “laws of nature” refer to real causal connections within external reality. Hume followed Locke in holding that all belief begins with “impressions”, i.e. sensations, passions, emotions, which are the primitive imprints of external objects on our passive sensibility. We then form “ideas” which are the recollections of these impressions, their “faint images” or “copies” in memory. Hume argued that what guides us in these recollections of impressions, and thus in the formation of ideas, is the associative law of similarity: impressions which are sufficiently similar to each other get mutually associated, and thus form an idea. For example, our sense impressions of particular fires start over time to evoke recollections of each other due to mutual association, and this gives us the general idea of fire. Finally, beliefs emerge because these ideas, too, get linked to each other on the basis of association. To give an obvious example: in the past we have often experienced one sort of impression, e.g. of smoke, as immediately following upon another kind of impression, e.g. of fire, and this causes the general idea of smoke to become associated with the general idea of fire. This, according to Hume, is the full extent of what we mean when we say “fire causes smoke”. There is nothing more to our concept of causality, according to Hume, than this regular, inductively based association of one idea with another:

“We have no other notion of cause and effect, but that of certain objects, which have been always conjoin’d together, and which in all past instances have been found inseparable. We cannot penetrate into the reason of the conjunction. We only observe the thing itself, and always find that from the constant conjunction the objects acquire an union in the imagination. When the impression of one becomes present to us, we immediately form an idea of its usual attendant […].” (Hume 2003 [1739-40]: 67)

For Hume, then, the necessity we associate with the laws of causality, i.e. the idea that if one thing happens then another thing must happen, is nothing but the strength of this association, the power exerted by habit over the workings of our minds. We project this feeling of necessity onto the world, seeing the connection between one object and another as a necessary link between cause and effect. But, according to Hume, this is just an illusion, albeit a very powerful one. If we analyse our ideas more closely, Hume argued, we find no intrinsic connection between them that could substantiate a causal claim, such as that fire causes smoke. Imprisoned as we are within the circle of consciousness, we cannot know the real causal connections between external objects, if there are any at all. All we can know, Hume concludes, are the impressions and ideas of those objects within consciousness, and the merely associative connections between those impressions and ideas. Thus the causal laws of natural science evaporate into subjective feelings of necessity as we have been habituated to associate one idea with another.

The Mind-Body Problem and the Crisis of the Causal Theory of Perception
In sum, the Way of Ideas fostered epistemological skepticism by imprisoning the knowing subject with the circle of consciousness, hiding external reality behind a veil of perception. But it fostered such skepticism also in another (though closely related) way, namely, by inviting the mind-body problem. For how can mind interact with the external and supposedly material world if they are so very different, as the Way of Ideas suggests? The external world, after all, insofar as we can know it, is knowable only through its primary qualities, such as solidity, spatial position, and motion. For all we know, therefore, external reality is nothing but solid bodies interacting mechanically in space. Hence, of course, Descartes’ definition of the external world in terms of “res extensa”. But consciousness is very different from this world of extension, since ideas appear to have no solidity, no weight, no well-defined spatial position (if ideas can be said to be in space at all, they must be somewhere in my head, but where exactly?), and they do not interact by bumping into each other as material bodies do. Moreover, the conscious subject appears to have the capacity for free will, but free will seems impossible in a material world governed by causal determinism (pace Hume). Thus, consciousness appears to be in an entirely different realm of being, the immaterial realm of “res cogitans” as Descartes put it. Locke, too, drew the conclusion that mind must be immaterial, and thus categorically different from the material world which we can know through its primary qualities.

But, to repeat, if mind and matter belong to ontologically distinct realms, how can they possibly interact? Descartes wavered on this question, sometimes allowing mind-body interaction in the pineal gland, at other times doubting the possibility of such interaction; to Princes Elisabeth of Bohemia, with whom Descartes corresponded extensively, he admitted that this problem vexed him greatly and that he had no good solution to it. Locke was more resolute in that he openly declared the problem insoluble, there being no possibility for mind and matter to interact, except through divine intervention. As Locke argued, all you can get from spatial form and motion are other spatial forms and motions, and since the contents of consciousness are neither spatial forms nor motions, they cannot be caused by matter; nor can they exert causal influence on matter. However, since mind and matter obviously do interact, Locke felt compelled – much like Descartes in his solution to the problem of skepticism – to invoke God, who must have “superadded” mysterious properties to material objects, over and above their essential primary qualities, rendering them capable to cause sensations and ideas. Thus in his Essay Concerning Human Understanding, Locke writes:

“[B]ody as far as we can conceive being only able to strike and affect body; and Motion according to the utmost reach of our Ideas, being able to produce nothing but Motion, so that when we allow it to produce pleasure or pain, or the Idea of a Colour, or Sound, we are fain to quit our Reason, go beyond our Ideas and attribute it wholly to the good pleasure of our Maker.” (Locke 1996 [1989]: 237)

Obviously, no skeptic will be persuaded by this appeal to God in order to explain mind-body interaction. That Locke feels compelled to invoke divine intervention in this context only goes to show the deepness of the problem. And apart from being an ontological problem concerning the place of mind in the material world, it is also an epistemological problem, and one that aggravates the skepticism already induced by the Way of Ideas. For insofar as the causal interaction between matter and mind becomes mysterious, it becomes equally mysterious how perceptions can convey information about external objects. For here the only possible theory seems to be some version of the causal theory of perception, such that perceptions carry information about external objects because they have been caused by these objects, i.e. by the impingements of material objects on our external sense organs. Locke accepted a causal theory of perception, and he used it to explain how we can know external objects. Although the secondary qualities caused in our minds by external objects do in no way resemble those objects, as Locke admits, the situation is different with the primary qualities, i.e. with our perceptions of solidity, spatial position, figure, motion, etc. Here, according to Locke, our perceptions do resemble the objects by which they have been caused. By causing perceptions in us, then, external objects convey to us information about their primary qualities. And, for Locke, this is the only way we can know external objects, since according to him all knowledge starts with sensory impressions, the mind being a tabula rasa prior to experience. Hence the dire consequences of the mind-body problem. If the causal interaction between mind and matter becomes mysterious, to such an extent even that we need to invoke divine interaction to explain it, then clearly the causal theory of perception is of little help in explaining the veracity of our perceptions. Due to the mind-body problem, then, the epistemic position of the subject under the Way of Ideas deteriorates even further: not only is the subject shielded from external objects by a veil of perception, imprisoned in the circle of consciousness; the only way for external objects to pierce through that veil – by causing perceptions in us that resemble their primary qualities – falls away by being a complete mystery. And even if we accept mind-body interaction as an unexplainable yet undeniable given, we still have the problem raised by Berkeley (following Democritus) that we really have no perception of primary qualities apart from secondary qualities… 

References

-Arnauld, A. (1964 [1662]), The Art of Thinking. Indianapolis: Bobbs-Merrill.

-Bennett, J. (1971), Locke, Berkeley, Hume: Central Themes. Oxford: Oxford University Press.
-Berkeley, G. (2003 [1710]), A Treatise Concerning the Principles of Human Knowledge. Mineola: Dover Publications.
-Descartes, R. (1996 [1641]), Meditations on First Philosophy. Cambridge: Cambridge University Press.
-Hume, D. (2003 [1739-40]), A Treatise of Human Nature. Mineola: Dover Publications.
-Locke, J. (1996 [1689]), An Essay Concerning Human Understanding. Indianapolis: Hackett Publishing Company.
-Stroud, B. (1984), The Significance of Philosophical Scepticism. Oxford: Oxford University Press.