Cartesian philosophy has come to be understood as an inaugural moment within modern conceptions of vision, and yet the status of this location may seem equivocal. For Martin Jay, Descartes stands as a pivotal figure within a tradition of 'ocularcentrism', against which much recent French thought has directed its criticism; but for Maurice Merleau-Ponty and an earlier moment of twentieth-century French thought, Cartesian philosophy is most notable for its hostility to vision and the visual (Merleau-Ponty, 1964A, pp. 159-92; jay, 1993, ch. 1). Underlying this apparently divergent reception is a certain ambivalence to vision in Cartesian thought: on the one hand it ties vision to the service of cognition while, on the other hand, it makes a fundamental distinction between knowledge and visual experience. Yet in fact this ambivalence makes possible its singular achievements. Descartes' aim was to escape the world of analogies, equivocations, and assertions that characterized medieval Scholasticism, and to discover instead a point that is certain and free from doubt in order to ground knowledge. His thinking of vision takes place within this project, and is organized around its central terms, certainty and doubt. The fundamental dynamic which drives Descartes' thinking of vision is a refusal to equate vision directly with knowledge, and this refusal opens the way for a characteristically modern conception of vision, in which sensory experience is distinguished from the cognitive framing or forming of sensation by consciousness. And it is only because visual experience cannot directly give rise to knowledge that vision becomes a cultural and philosophical issue for modernity, rather than a problem only for optics or neuropsychology.
If vision plays an important role in Cartesian thought, technology provides the conceptual mechanism which allows it this function. The scientific investigation of vision, and the new optical technologies to which it gave rise, embodied within visual experience a broader anxiety over the security of knowledge that was prevalent in early modern Europe. Economic and political transformations within the borders of Europe, coupled with military and commercial expansion beyond, saw the emergence of alternative explanatory models and new contexts of experience which left traditional assertions of certainty looking increasingly limited and arbitrary. For many of Descartes' contemporaries, the achievement of certainty involved forgoing the security of appeals to tradition and revealed religion, and the subjection of knowledge of the world to the test of empirical observation. But for Descartes, this wider uncertainty also emerges within empirical perception itself, given the epistemological questions raised by early modern science, by new instruments like the telescope, and by the representational techniques of Renaissance and Baroque art. If
Descartes joins his contemporaries in refusing the convenience of appeals to tradition or faith, he also rules out the most obvious alternative for establishing such a point of certainty, namely the self-evidence of empirical perception. For Descartes, just as much as religion, empiricism is also understood to involve a series of leaps of faith: one must have faith in the visual distinctness and availability of objects, in their willingness as it were to show themselves as they really are; one must have faith that visual data are communicated accurately to the eye and in a way that resembles the sensible world; one must have faith that the bodily reception and transmission of sensory data are not subject to distortion; and one must have faith that consciousness reproduces the visual world in all its richness and complexity.
Descartes' awareness of the uncertain nature of visual experience grew out of a sustained interest in vision and the emergent science of optics: he conducted optical research, speculated on lens design, and wrote on optics and light not only in his Optics, but also in his ambitious account of the physical universe, The World, written between 1629 and 1633 (1998). As such, Descartes' thought is informed by the broader reconceptualization of vision occurring in seventeenth-century thought.' The first effective telescope, developed by Galileo Galilei and announced in his Sidereal Messenger of 1610, led to a series of discoveries which bore out the astronomical models of Copernicus and subsequently Kepler.2 The observation of Jupiter's satellites, Saturn's rings, the mountainous surface of the moon, sunspots, and a multitude of stars previously too small to see with the naked eye, all proved difficult to explain within the existing Aristotelian accounts of the cosmos. In terms of natural philosophy, the heliocentric planetary system revealed by the telescope pointed to a universe operating according to mathematical laws which could be calculated and predicted. In particular, the advances made by Kepler in calculating elliptical orbits encouraged a style of inquiry which depended on mathematical proofs and prediction, rather than the authority of the ancients or reference to the Bible. Kepler's extension of this mathematical approach to the telescope itself in his Dioptrics (1611) included
1 For an account of this interaction, see Garber, 2001.
2 For an account of this history, see Park, 1997, ch. 6.
light and the action of lenses within this mathematically organized and predictable world. However, the reformulation of the visible world on mathematical principles was not unequivocally comforting, nor did it necessarily lead to a renewed faith in the certainty and self-evidence of vision. Rather, the extension of geometrical and mathematical models to the behaviour of the observable world and to the action of light pointed to the necessity of supplementing visual experience with modes of investigation and understanding which are not given in visual experience, but which involve a distinctly non-visual, conceptual cognition. This unsettling effect was replicated at the level of visual experience by the telescope itself, which introduced an alternative image-world with its own parameters of scale and resolution, an effect heightened by the spherical and chromatic aberration inherent in optical lenses.
The impact of the telescope and the new sciences of astronomy and optics on existing understandings of vision was further complicated by developments in the representational techniques of visual art. Just as the art of lens manufacture upset the contemplative stance of natural philosophy by pointing to a world of mathematical principles underlying sensory experience, so other arts also contributed to this process, not least painting. Leon Battista Alberti's On Painting (1435) offers a practical methodology for single-point perspective, based on the vanishing point as the organizing principle of the picture plane.3 While Alberti's text is more concerned to offer a practical guide than a mathematical exposition, and while he famously claimed that the artist is concerned only with what is directly available in visual experience, his method depends on an initial geometrical organization of the picture plane which, although subsequently effaced, underpins the resulting representation. The visual self-evidence of the perspectival image thus rests on an invisible armature constructed according to the principles of Euclidean geometry. Once again, the identification of a mathematical form underlying appearances raises questions about the credibility of visual experience, rather than straightforwardly reinforcing it. After all, single-point perspective allowed painters to
' For an account of the impact of single-point perspective on understandings of vision, see Park, 1997, ch. 5.
render an image of a three-dimensional world upon a plane which existed in only two, an achievement which points more to the gullibility of the eye than to its reliability as a guide to empirical truth. As much as furthering claims to a certain 'realism' in visual art, singlepoint perspective raised all the more urgently the question of illusion and the propensity of vision to mistake illusion for truth; perhaps not surprisingly, the dissemination of perspectivalism in the Renaissance and Baroque was accompanied by a renewal of interest in trompe-l'oeil, anamorphosis, the distorting effect of mirrors, and the camera obscura.
The doubts concerning sensory perception raised by representational techniques, optical technologies, and the new science, play a crucial role in Descartes' theoretical philosophy, underpinning its understanding of vision. In the Meditations on the First Philosophy (1641), for example, the disparity between the image of the sun seen by the naked eye and the knowledge derived from the rational calculations of astronomy is seen to indicate the inherent uncertainty of sensory experience: this disparity demonstrates 'that the idea which seems to have emanated most directly from the sun itself has in fact no resemblance to it at all' (1988, p. 90). Such uncertainty, however, is not restricted to the heavens nor provoked only by the telescope. In the Second Meditation, Descartes offers the more everyday scenario of looking out of a window across a square where men are passing. While accepting that we 'normally say that [we] see the men themselves', Descartes asks what exactly we do see, above and beyond 'hats and coats which could conceal automatons'. The point here for Descartes is that what we take for immediate perception 'is in fact grasped solely by the faculty of judgement which is in [the] mind'; we do not see the men in all their substantial reality, but rather we register certain images through which we 'judge that they are men' (ibid., p. 85). What emerges here is the way in which the technological manipulation of the visible world, whether through optical instruments like the telescope, or through more down-to-earth mechanical devices and tricks, points to a fundamental division between visual data on the one hand, and the operation of the thinking consciousness on the other. In the Optics this role can therefore be extended to include not only the technology of visual reproduction in the form of engraving, but also the technique of single-point perspective. Descartes points out that although engravings consist 'simply of a little ink placed here and there on a piece of paper, they represent to us forests, towns, even battles and storms'. Again, the disparity between the minimal visible marks of an engraving and the 'countless different qualities' which they evoke for consciousness is emphasized by the technique of single-point perspective, where circles are represented by ellipses and squares by rhombuses: 'it often happens', Descartes observes, 'that in order to be more perfect as an image and to represent an object better, an engraving ought not to resemble it' (1988, pp. 62—3).
The central issue here for Descartes is not to decry the distortions of optical instruments or the misrecognitions thrown up by city life, nor to denounce single-point perspective as an especially illusionistic technique, or engraving as a particularly distorting technology of reproduction — all projects which tend to imply the necessity of rediscovering an immediate and direct mode of visual perception uncontaminated by technology or technique. Rather, Descartes deploys instances of technologically and technically mediated images in order to exemplify the working of vision per se: as he says of the example of the engraving, 'we must think of the images formed in our brain in just the same way' (ibid., p. 63). Descartes' allusion to technologically mediated vision is not merely rhetorical, nor does it simply provide a convenient metaphorical device to drive his argument at particular moments. On the contrary, technology plays an important role in illuminating the nature of visual experience and its relationship to cognition. For Descartes, new lens technologies like the telescope, and illusionistic techniques such as anamorphosis or single-point perspective, reveal something which was already there in 'normal' or 'everyday' vision: namely, the difference between the mental act of perception and the mechanical processes involved in the transmission of light and of sense data in the nervous system. The importance of technology and technique, therefore, is that they crystallize out this mechanical operation, forcing us to acknowledge the mathematical ordering underlying visual experience. For Descartes, there is no opposition between technologically mediated and 'pure' vision, because all vision is 'technological' in a very direct and immediate sense.
This understanding returns us to the topos of doubt, and begins to indicate why vision plays such an important role in charting or defining the very nature of doubt. The Cartesian understanding of visual experience as mechanical or 'technological' undermines empirical sense certainty, demonstrating that we do not immediately perceive the world as it 'really is'; therefore we cannot locate sensible perception as a point of certainty, because when taken in isolation it is inherently subject to uncertainty and doubt. However, Cartesian philosophy attempts to harness the disruptive potential of this doubt, employing it as a kind of homeopathic cure for epistemological uncertainty. Thus in the first person narrative of the Meditations, doubt is not an involuntary state inadvertently suffered by Descartes, but a consciously chosen method through which certainty is to be achieved, the necessary and indispensable first step for proceeding towards certain knowledge. In order to identify what is truly certain and indubitable, Descartes proposes that first he must suppose 'that everything I see is spurious', that 'body, shape, extension, movement and place are chimeras', that 'I have no senses', and therefore that 'my memory tells me lies, and that none of the things that it reports have ever happened' (ibid., p. 80). The fundamentally illusory nature of sensory experience is presented most memorably in the First Meditation's fiction of the malicious demon, a hypothetical entity 'of the utmost power and cunning' who has 'employed all his energy and power to deceive'. The point of this fiction is to encapsulate economically the conception of vision emerging from Descartes' optical studies and his understanding of visual art; its effect is to block contemporary accounts of the self-evidence of sensory experience, whether based on the teleology of divine creation or the certainty of empirical perception. At a stroke Descartes has lost the sensible world in all its richness and complexity, and must assume 'that the sky, the air, the earth, colours, shapes, sounds and all external things are merely the delusions of dreams which he has devised to ensnare my judgement' (ibid., p. 79).
However, despite its apparently all-encompassing nature, Descartes' radical doubt has very definite limits, and it is precisely the demarcation of these limits which allows him to establish certainty. For if we cannot be certain that the ideas which fill our consciousness correspond to objects existing 'out there' in the world — they might after all be dream images, which provide the same experiential intensity as waking perception even though our eyes are closed — we can at least be certain that we are thinking them. Even if what I am thinking is illusory, argues Descartes, the fact that I am thinking is certain and indubitable. This inner certainty establishes a fundamental opposition between thinking substance (res cogitans), understood as soul and mind, and extended substance (res extensa), the corporeal world which comprises not only inanimate but also animate nature. This distinction reposes the question of knowledge and its relationship to visual experience by bracketing the question of vision, or the sensory perception of extended substance, and focusing attention on the operation and nature of consciousness instead. The activity of the cogito is described throughout the Meditations in terms of an internal self-perception or inner vision: 'when the mind understands' we learn in the Sixth Meditation, 'it in some way turns towards itself and inspects one of its ideas which are within it' (ibid., p. 111). Mental perceptions which are perceived both clearly and distinctly are taken by Descartes to be certain and indubitable, and so the self-certainty of the cogito arises from the clarity and distinctness of its mental self-perception revealed in the 'natural light' of thinking. The cogito's own act of self-perception allows Descartes to establish the existence of the 'I' as thinking substance, and that of a perfect and infinite entity underlying it, namely God.
If the initial separation and opposition of thinking and extended substance makes possible the cogito's self-certainty, it also implies an analogous division and hierarchy within consciousness itself between the clear and distinct ideas of pure understanding and the more confused ideas derived from sensory perception. The issue of knowledge thus becomes a question of the degree of clarity and distinctness of particular mental perceptions, and once the notions of number and duration have been secured as innate and indubitable, their application to sensory perception allows the inherent clarity of extension, shape, position, and movement to be derived — that is, the basic mathematical co-ordinates of mechanics and Euclidean geometry. Given that the existence of extended substance is understood to be guaranteed by God, Descartes is now able to return to sensory experience a measure of certainty, albeit in very narrowly defined terms. Corporeal things 'may not all exist in the way that exactly corresponds with my sensory grasp of them', concedes the Sixth Meditation, 'since in many cases my grasp of them is very obscure and confused'; yet crucially they must 'possess all the properties which I clearly and distinctly understand', namely 'all those which, viewed in general terms, are comprised within the subject-matter of pure mathematics' (ibid., p. 116). Cartesian thought loses the world only to re-establish it once again, but it does so on a new footing which, notwithstanding its reliance on the residues of Scholasticism, is recognizably modern. However, it does so at a cost. Notoriously, Cartesian rationality excludes the body and its inhabitation of the world from cognition, and reduces the coordinates of visual experience to the fixed three-dimensional space of Euclidean geometry and the linear causality of mechanics.
The particular significance of Descartes' 'technological' understanding of vision lies in its role in redrawing the relationship between visual experience and knowledge, so making possible the separation which underpins the Cartesian subject and its epistemological certainty. This role becomes clearer when Cartesian vision is set against the Scholastic conceptions of sensible forms and empiricist conceptions of the receptivity of the senses. Within medieval Scholasticism, vision was understood to occur through the migration of 'intentional' or 'sensible' forms — in Latin species or simulacra, in Greek eidola. These species are understood as fixed images that peel off from substances and fly through the air into the perceiver's soul by way of the sense organs (see Park, 1997, pp. 100—7). From a Cartesian perspective, a certain homology emerges here between Scholastic tradition and the emergent empiricism: however different their conceptions of vision might be, what they both share at the very least is a certain conception of transmission or resemblance. For Scholasticism, substances emanate species which migrate to the eye, directly transferring the sensible form of the object to the perceiver's soul; for empiricism, the form of the object impresses itself upon the perceiver's mind through the senses. In each case, the mental image produced resembles or directly reproduces some quality or aspect of the object or substance, however conceived. The reason why instances of technologically mediated sight best exemplify the working of vision for Descartes is that they interrupt both empiricist and Scholastic accounts of resemblance by dramatizing the difference between the mechanical operation of light and the eye on the one hand, and the operation of the soul or thinking substance on the other. This conception of the relationship of knowledge and vision is fleshed out in the example of the engraving offered at the beginning of the Optics. The engraved image is formed in terms of the representational conventions of artistic technique, and cannot be said to embody the form of the object itself; equally, as a discrete and artificial object, it cannot be said to emanate the species or sensible forms of the substances which it represents. That we nonetheless recognize the image produced indicates to Descartes that the 'problem' is not how mental images 'resemble' objects, but 'how they can enable the soul to have sensory awareness of all the various qualities of the objects to which they correspond' (ibid., p. 63). Light, which is conceived of by Descartes as an excitation of extended substance, produces a corresponding excitation in thinking substance, or the soul, by way of the mediation of the pineal gland, which provides the linkage between these otherwise incompatible substantial realms. Mental perception is therefore to be thought of as an excitation within thinking substance which corresponds in its own terms to a quite different mode of excitation in the fundamentally incompatible realm of extended substance (1998, pp. 124—39). Cartesian vision might be thought of as an act of translation or transcription from one quite distinct mode or 'language' into another, in which no direct transmission or transference takes place. In terms of Michel Foucault's typology in The Order of Things (1970), this redrawing of the relationship between vision and knowledge marks the movement from a conception of knowledge based on resemblance to one based on representation.
Perhaps the most forthright expression of Descartes' new conception of the relationship between knowledge and visual experience is offered in the opening pages of the first part of The World, entitled 'The Treatise on Light', where vision is described by way of an analogy with speech. Descartes' analogy of sight and speech is both distinct from Rousseau's later conception of speech and in certain senses close to post-Saussurian conceptions of linguistic signification. Like visible rays, speech is conceived of by Descartes as an excitation within extended substance — as vibrations in the air — and thus the relationship between words, as extended substance, and their meaning, as thinking substance, is arbitrary or conventional, a point reinforced by the existence of different languages. If a jump is possible in the case of speech between arbitrary patterns of sounds waves and mental perceptions which clearly bear no resemblance to them, Descartes argues that such a jump must also be plausible in the case of vision:
Now if words, which signify something only through human convention, are sufficient to make us think of things to which they bear no resemblance, why could not Nature also have established some sign which would make us have the sensation of light, even if that sign had in it nothing that resembled this sensation? And is it not thus that Nature has established laughter and tears, to make us read joy and sorrow in the face of men (ibid., p. 4).
Although the talk here of a providential nature sits uneasily alongside Cartesian claims to explain the physical world in terms of efficient rather than final causes, the subsequent account of light and corporeal substance in both The World and the Optics describes a universe of inert, extended matter explainable through mechanical action; that is, precisely the mathematically predictable world implied by single-point perspective and early modern science. Notwithstanding its baroque expression, the model of vision enabled here by analogy with the conventional nature of linguistic signification does not involve the resemblance of mental images to physical objects, in the sense of a direct transference of the object's form to consciousness; instead, vision is to be understood not as resemblance, but as formal correspondence. And indeed, the terms of this formal correspondence are already in place: the self-inspection of consciousness identifies reason in terms of the clarity and distinctness of pure mathematics, while the world of extended matter is understood in terms of geometrical space and mechanical causality. Without such an a priori and transcendent notion of form, however, this analogy would simply beg the question as to why excitations in extended substance should give rise to mental perceptions which in some way correspond to them, rather than just producing random effects.
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