Is Reid’s conception of visible figure compatible with his
direct realism about perception?

I. Introduction

According to the theory of perception set out in Thomas Reid’s Inquiry into the Human Mind on the Principles of Common Sense (ihm, Reid 1997) and Essays on the Intellectual Powers of Man (eip, Reid 1865), our perceptual knowledge of objects in the external world is both epistemically direct and non-inferential. Whilst there has been much debate about the precise nature of Reid’s realism (e.g. Buras 2002; DeRose 2004; Copenhaver 2000, 2004; Pappas 1989) and whether it can be properly described as direct, one aspect of his account remains poorly understood, namely his account of visual perception. According to Reid, the ‘immediate objects of sight’ (ihm 102) are not macroscopic objects in the external world, as for each of the other four senses, but what Reid variously describes as ‘visible or perspective appearance[s]’ (ihm 81), ‘apparent figure[s]’ (ihm 82) and, most commonly, ‘visible figure[s]’ (ihm 95–103). In this essay I will examine the precise nature of these entities and whether they undermine Reid’s direct realism since, if the immediate object of perception is also the direct object, then this appears to conflict with the thesis that we have direct access to objects in the external world by means of visual perception.1

In order to motivate my argument, I will first give a brief summary of Reid’s theory of perception, followed by an account of his notion of visible figure. I will then consider the philosophical basis for Reid’s direct realism and how this might be undermined by the existence of visual intermediaries. Finally, I will argue that it is possible for Reid to maintain his commitment to direct realism in spite of the non-immediate nature of visual perception on the grounds that visible figure is related to and derivable from the real qualities of objects. In doing so, I will present an interpretation of Reid’s theory that highlights the role of his ‘doctrine of signs’ — an element of Reid’s philosophy that is often overlooked, but which, I argue, plays a more central part in his account of visual perception than might first appear.

II. Sensation and Perception

In contrast to the so-called ‘theory of ideas’ (eip 111) held by Descartes, Locke and Hume, amongst others, Reid rejects the notion that the objects of perception are mere ‘ideas’ or impressions within the mind in favour of a direct realist theory of perception. According to Reid, the object of perception, what I shall call its intentional content, is not some ‘idea’ or impression within the mind, but the object or objects in the external world that we normally take the perception to be about. Moreover, the conception and belief arising from sensory experience, and that is not, for Reid, the result of an inferential or rational cognitive process. Instead, the mind is said to proceed immediately from the ‘sign’ of an external object — e.g. a sensation of touch or smell — to what is ‘signified’, i.e. the object itself, thus placing us in direct epistemic contact with the external world. This may be contrasted with, for example, Hume’s (1737: 1.1.1) account, which leaves an ‘epistemic gap’ between the immediate objects of perception — in Hume’s case, impressions in the mind — and those in the external world, thus creating the possibility of the sort of systematic scepticism that Reid considered to be so abhorrent to common sense (ihm 28).

Central to Reid’s account is the distinction between sensation and perception — a distinction which he was chiefly responsible for defining (Price and Gibson in van Cleve 2003: 104). For Reid, a sensation is a ‘simple act of mind’ that ‘accompanies’ perception (eip 15) and whose character is open to rational reflection — or what contemporary philosophers might call a ‘raw feel’ or quale. The archetypal example of a sensation concept is that of pain where the subject is conscious of a certain feeling, but not of any particular object that the feeling is about; i.e. it has no intentional content (although it will of course have some internal or external cause). Whether by virtue of our constitution or through association by means of experience, sensations function as ‘signs’ of the internal or external states that occasion them. Thus, in contrast to so-called sense-data theories of perception, they do not acquire meaning through any intrinsic ability to bear information, but rather stand in extrinsic relations to the external events that they signify (Copenhaver 2004: 71–2). Perception, on the other hand, is comprised of what Reid calls ‘conception and belief’ (ihm 168), and is the bearer of intentional content (ibid.). For Reid, the perception — of a seagull, for example — is about its object (the seagull) in a way that the sensations of sound and colour that accompany it are not.2 Reid’s notion of ‘conception’ is subtle and complex,3 but his intention is to distinguish between what is felt and what is perceived, with the intentional content of perception always being some object or objects in the external world rather than an ephemeral ‘idea’ or sense-impression as per the theories of Descartes and Hume.

Reid explicitly states that sensations are not themselves objects (except in the trivial grammatical sense; ihm 167–8), but rather aspects of the act of perceiving that have ‘no distinction from the act of mind by which [they are] felt’ (ibid.). Thus, ‘feeling a pain has no more significance than being pained’ (ihm 108; original emphasis).4 This has led some commentators (e.g. Pappas op. cit: 162 and van Cleve op. cit: 104) to take Reid as advancing a kind of adverbialist theory of sensation, although this is perhaps an overstatement since his account is motivated mainly by epistemic and phenomenological concerns, and lacks the necessary ‘systematic structure’ for full-blown adverbialism (Nichols 2007: 85). Nevertheless, it is crucial to Reid’s direct realism that he does not classify sensations as objects since this would make them the direct objects of perception, as per the theory of ideas, instead of external mind-independent objects. Were this the case, then we could no longer be said to be in direct epistemic contact with the external world, thus undermining Reid’s primary argument in favour of realism and against scepticism. This is particularly relevant in the case of visual perception, whose only sensory component is that of colour (ihm 99), with the rest of what is seen being explained in terms of Reid’s notion of visible figure. Unlike sensation, however, visible figure is described as being both objective and mind-independent (Nichols op. cit: 122), and is therefore, even by Reid’s own admission, the ‘immediate object’ of visual perception (ihm 102).

III. Visible Figure

A sizeable part of Chapter VI of Reid’s Inquiry (§§7–19) is devoted to describing the non-Euclidean geometry of visible figure, as established by empirical and geometrical study. This in itself is quite remarkable given that the necessary mathematical formalism would not yet be developed for another hundred years by German mathematician Bernhard Riemann (Torretti 2007). Reid describes visible figures as ‘real and extended object[s] to the eye’ (ihm 101), differentiating them from both the ‘real’ (i.e. actual) figures of objects (ihm 96) and from sensations, for the following reasons:

1. 1.Visible figure contains representational structure concerning ‘the position of [an object’s] several parts with regard to the eye’ (ibid.), unlike sensation whose significance is extrinsic to its content, as described above.
   

2. 2.Any competent perceiver looking from a particular point of view and direction would perceive the same visible figure (ihm 84–5; Nichols op. cit: 122), thus making visible figure an objectively accessible feature of reality rather than a subjective act of mind as in the case of sensation.
   

3. 3.Visible figures have both form and extension, and thus resemble their objects (ihm 98). Sensations, which are mental, are incapable of extension — as established by Berkeley (ihm 90–5) — and have ‘no direct object distinct from the act [of mind] itself’ (eip 19).
   

4. 4.Visible figure may be derived mathematically by projecting ‘right lines’ (ihm 96) from the surfaces of objects to the part-spherical surface of the perceiver’s retina. This procedure may even be carried out by someone who is blind,5 making visible figure, unlike its tactile, auditory, olfactory and gustatory equivalents, accessible to those who lack the requisite sense — albeit minus the sensation of colour (ibid.).
   

For these reasons, Reid concludes that visible figure ‘cannot be called an impression upon the mind’, i.e. a sensation, ‘without the grossest abuse of language’ (ihm 100–1).

On Reid’s account, however, visible figure does have some features in common with sensation. Like sensation, visible figure functions as a ‘sign’ for external objects which is quickly ‘passed over’ by the mind and replaced by the perception (i.e. conception and belief) of those objects (ihm 168). This is illustrated by Reid’s example of the painter (ihm 102), who creates reproductions not of objects per se but of their visible figures such that any normally sighted observer would (according to the accuracy of the likeness) immediately recognise the resulting image as a ‘sign’ of the objects depicted.6 As with sensations, visible figures may also become the objects of conscious thought. The painter, for example, trains himself to perceive visible figures directly, as opposed to the objects that are normally signified by them (ihm 83), thus making conscious what is usually ‘passed over’ by the mind to such an extent that ‘it never had a name in any language’ prior to Berkeley (ihm 101).

Despite the above similarities, however, the lack of any compelling phenomenological evidence for a distinct sensation associated with vision (other than that of colour, which is uncontroversial) leads Reid to conclude that it is visible figures, not everyday objects, that are the immediate objects of our visual perceptions. This makes sight unique amongst the five senses in that it is the only one to not have everyday macroscopic objects as its intentional content. This appears to place Reid’s notion of visible figure in conflict with his direct realism since, if the immediate object of perception is also taken to be the direct object of perception, our epistemic access to the world by means of vision must also be indirect since, by Reid’s own admission, it is mediated by visible figure. Nichols (op. cit: 109) has suggested that this tension may represent a deliberate trade-off between the parsimony and explanatory power of Reid’s theory, or that he may even have been unaware of its full implications (ibid. 111). However, this is implausible since Reid would hardly have advanced an account that was so obviously guilty of the error for which he rejects the theory of ideas. In order to examine this claim more closely, we must therefore establish the precise nature of Reid’s direct realism.

IV. Direct and Indirect Realism

George Pappas (1989: 156) identifies two distinct forms of direct realism to which Reid subscribes: ‘perceptual direct realism (PDR)’ and ‘epistemic direct realism (EDR)’ (ibid.). According to PDR, external objects exist independently of the perceiver and are the bearers of at least some of their perceived qualities — typically the primary qualities of figure and extension. PDR therefore accounts for the realist aspect of Reid’s theory. EDR, on the other hand, entails that we have immediate non-inferential belief about such objects — a position that Reid clearly endorses throughout the Inquiry (e.g. ihm 81, 168, 172). It is this condition of immediacy within PDR that is called into question by Reid’s notion of visible figure, and that threatens to undermine his direct realism. Whilst it is relatively trivial to define ‘direct’ in such a way that Reid comes out as a direct or indirect realist according to the chosen definition, a more pressing question is whether PDR really does require the ‘immediacy’ of visual perception. It is therefore important to ascertain the relationship between immediacy and directness in Reid’s account, as well as the precise meaning of ‘immediate’ in this context. To this end, I will consider several means by which the intentional content of perception might be determined before moving on to examine how this process might be affected by Reid’s conception of visible figure.

We can first rule out the idea that Reid’s theory of perception involves some kind of ‘mythical’7 connection between mind and world in which there are no intervening stages whatsoever. Reid’s himself describes many mediating entities, including light rays, which communicate the visual appearance of objects to the eye, and impulses within the sense organs and nervous system (although the latter should not be identified with sensations since they occur in the body rather than the mind [ihm 100]). All forms of perception are thus mediate in some sense, and so the presence of an additional mediating entity in the form of visible figure should not necessary cause us to conclude that Reid’s theory is epistemically indirect.

Analysing perception in terms of causal relations presents a similar difficulty in that every perceptual event is itself preceded by a complex chain of events. Light strikes the surface of an object, some of which is reflected towards the eye causing an image to be formed on the surface of the retina, which in turn causes an electrical signal to be transmitted to the brain, and so on. Clearly we do not take the light (not to mention the nuclear reactions on the surface of the sun that caused it to come into existence) to be the intentional object of perception. The intentional content of perceptions must therefore be fixed by some factor other than mere causal connection. Furthermore, whilst it is tempting to assume, as per Pappas (op. cit: 160) and Buras (op. cit: 462), that Reid takes bodily impressions to be the cause of sensations, which in turn cause perceptions, Reid himself never uses this term and should not be read as such. Indeed, he points out the ambiguity of the word ‘cause’ (ihm 40), whose vulgar use signifies little more than constant conjunction, the direct perception of which had already been ruled out by Hume (op. cit: 1.3.2), regardless of whether there is any genuine efficacy. Furthermore, Reid denies any knowledge of the nature of the connection between bodily and mental phenomena, declaring it to be most ‘unaccountable’ (ihm 91). Reid’s language is rather that of occasionalism in which an external object ‘occasions’ or ‘suggests’ sensations that subsequently give rise to a corresponding perception, but without any specific account of the mechanism by which these events take place (except for the presence of the mediating entities described above).8 Reid does, however, give a clear indication of sequence, describing perception as a ‘process’ or ‘train of operations’ (ihm 174) in which sensation is ‘followed by’ conception and belief (ibid.). Whilst this might be suggestive of some as yet undiscovered causal mechanism, Reid conspicuously stops short of claiming that one stage causes the other. We should therefore be wary of attributing any substantive role to causation in fixing the intentional content of perception within his theory.

Perhaps a more productive method of establishing the intentional object of visual perception may be given in terms of a counterfactual analysis of its necessary and sufficient conditions. When I see an object — a tree, for example — this forms both the occasion for and content of my perception, thus giving rise to the conception and belief that there is a tree before me. Were the object not present then I would, by definition, be unable to perceive it — a hallucination, for example, would not count as a case of perception for Reid. The same cannot be said of sensations, since although I might not be conscious of any particular sensation that accompanies the perception — the colour of the tree, for example — I can still be said to perceive the tree. This is arguably the case with many non-visual perceptions, since I am not necessarily aware of the particular sensation of touch beneath my fingers, but rather of the table, or of the scent that is emanating from the kitchen, but of my dinner as it is cooking in the oven. Thus, although sensations may ‘occasion’ or give rise to perceptions, experiencing the sensation is neither a necessary nor sufficient condition for perception.9 Conversely, visible figure is similarly insufficient for perception since all visible figures are of some actual object or objects, without which the visible figure could not exist. Sensations do not fit this description since they are neither objects in their own right nor intentional, and may often be absent from perceptual experience. Visible figure, on the other hand, is both objective and necessary for visual perception — in humans, at least — but cannot exist independently of a particular point of view and an object. This gives us some clue as to its true nature, as I will explore in the following section. We can imagine, however, that visual perception, or something very much like it, might be possible for some creatures (although not for us) in the absence of visible figure, suggesting that it is only objects and not their visible figures that are necessary for perception to take place (cf. ihm 176; Nichols op. cit: 137).

The above considerations may be restated more clearly as the claim that there is an internal relation between an object, perceiver and visible figure such that the third cannot exist in the absence of the first. Consequently, whilst visible figure may be the ‘immediate’ or ‘direct’ object of visual perception in a strictly literal sense, it does not constitute the intentional content of the perception — i.e. the external object with which we are cognitively acquainted (van Cleve op. cit: 119) — since it cannot exist independently of that object. However, this leaves us with a puzzle. We have established that visible figure fulfils the same role in Reid’s account of visual perception as sensation does in the case of the other senses; i.e. as the ‘sign’ of some external object(s). However, it now seems as if we have two direct objects of visual perception: the ‘immediate object’ or ‘sign’ (visible figure) and the external object(s) that it signifies. Reid himself acknowledges as much, stating that

the thing signified, when it is introduced to the thought, is an object of thought no less immediate than the sign was before: and there are here two objects of thought, one succeeding another […].

eip 85 in Nichols op. cit: 196 (emphasis mine)

Whilst this duality is helpful in explaining certain types of visual phenomena, such as the way that a circular plate can appear to be both elliptical (its visible figure) and round (its actual figure) (ihm 79), or the apparently small size (visible figure) of a distant object whose actual size or figure remains constant (ihm 84), it fails to settle the issue of Reid’s direct realism since it is no longer clear which sense of ‘direct’ is operating here. In the following sections, I shall therefore examine the relation between objects, visible figures and perceivers that is central to understanding Reid’s theory of visual perception.

V. Relational Properties

As has already been established, visible figure is both the ‘immediate object’ of visual perception and mathematically derivable from the actual location and forms of external world objects relative to the eye. Whilst it is clear that, for Reid, visible figures are not sensations but objectively accessible features of the external world, it is less clear precisely what kind of features they are. Reid himself professes to be at a loss as to which metaphysical category they should belong (ihm 98), suggesting that there is something peculiar about the ontological status of visible figure as compared to concretely existing objects in the external world. According to Nichols (2002: 61), this peculiarity may properly be attributed to its relational character.

Visible figures are ‘real’ in the sense that they are reliable signs of external objects that are accessible to all visually able perceivers (unlike sensations, which are mental entities, and so private to each individual). Despite being the immediate objects of visual perception, however, their existence is dependent upon the relationship between the location and orientation of the perceiver’s eye and the external objects that fall within its view (ibid: 123). This is why even non-visually able perceivers are able to derive the properties of a given visible figure geometrically from the relation between the surfaces of external objects and the eye — a fact that is frequently emphasised by Reid (e.g ihm 95). Visible figure, therefore, belongs to the ontological category of relational properties — or, more accurately, sets of relational properties — whose existence is contingent upon that of objects and some kind of perceptual apparatus resembling the human eye; i.e. a concave spherically-shaped projection surface. This does not render visible figure mind-dependent since its properties are determined by the physical geometry of the eye (Nichols 2007: 115) rather than the conscious awareness of the perceiver. Indeed, different kinds of visible figure may be derived for different kinds of surfaces; e.g. a perfect Euclidean plane, or a centrally magnifying lens as possessed by vultures and other birds of prey (Snyder and Miller 1978). There are, in fact, an infinite number of possible visible figures for any given set of objects, only a tiny fraction of which we are able to detect with the naked human eye (cf. Nichols 2007: 119). In each case, however, such figures are derivable from the real properties of objects relative to the eye, and so both objective and mind-independent.

Having established that visible figures consist of relational properties, we might legitimately ask whether there is any evidence as to whether Reid is a realist about such properties. As Nichols (op. cit: 122) points out, Reid makes it clear that relations such as the fact that ‘my foot is longer than my finger’ (eip 293) can be perceived immediately and non-inferentially, just as for visible figure. However, whilst this lends support to the notion that visible figures are relational and gives good reason to believe that Reid is a realist about visible figure, it does little to ascertain the epistemic directness of his account of visual perception. Indeed, one might argue precisely the opposite on the grounds that if visible figures are real and external to the eye then it is they, and not the external objects that they signify, that are the direct objects of perception. To clarify this issue, we must instead turn to what I will call Reid’s ‘doctrine of signs’.

VI. Reid’s Doctrine of Signs

Throughout the Inquiry, Reid repeatedly likens the sensible and visible ‘signs’ that lead the mind to form non-inferential conception and belief to a kind of ‘visual language’ (ihm 82, 166, 190). To the modern reader, this might seem like little more than rhetorical flourish, but given Reid’s disdain for the ‘way of analogy’ (ihm 203), it seems reasonable to assume that this comparison represents an important part of his overall theory. Central to this ‘doctrine of signs’ is the idea that in recognising or ‘interpreting’ (ihm 189) a sign, the mind immediately and involuntarily forms both conception and belief concerning the thing that is signified, in this case an object in the external world. According to Reid, there are three ways in which such associations may be established: (i) innately, by virtue of our natural constitution, as in the case of colour, (ii) acquisition by custom or habit, as in the case of depth perception, and (iii) through the operation of reason (ihm 177). Once established, however, even in the case of associations acquired through habit, the transition from sign to what is signified occurs solely in virtue of our physical and mental constitution, and not through any process of logical reasoning or inference (Copenhaver 2004: 70; ihm 81). As such, the formation of new associations in cases (ii) and (iii) may be seen as a way of preparing the mind to make similar such non-inferential associations in future, as opposed to involving the acquisition of any kind of knowledge concerning the link between signs and what they signify. In many cases (e.g. sensations) we may not even be aware of the ‘sign’, which immediately gives way to an awareness of the object itself. However, since both visible and real figure may be made the direct object of perception when attended to accordingly, this creates the impression that there are two direct objects of vision. It is only when we examine the respective role of each of these objects within the perceptual process that the distinction between sign and signification becomes clear.

For Reid, visible figure therefore performs the same function in the case of visual perception as sensation does for non-visual perception; i.e. as a sign for external objects (cf. ihm 186). Thus it is not that visual perception is indirect due to by the presence of visible figure, but rather that visible figure is itself an intermediate, non-causal stage in the formation of a fully fledged visual perception. On this view, it is correct to say both that visible figure is the ‘immediate object’ of visual perception (since it is the objective entity that we initially perceive) and that visual perception is direct (since the perception of visible figure immediately gives way to the perception of external objects by means of the natural operation the mind, just as with each of the other senses).10 We can therefore make sense of Reid’s claims about the directness of visual perception by interpreting his theory within the context of his doctrine of signs. Combined with the derivability of visible figure from the relational properties of objects with respect to the eye, Reid’s claim that the former is the ‘immediate object’ of visual perception does not affect the epistemic directness of his account in any important sense. We are able to see external objects by virtue of their relational properties with respect to the eye. This perceived or visible figure then gives way to a fully-fledged conception and belief concerning the object whose existence it signifies, which then forms the direct intentional content of our perception.

VII. Problems for Reid

The above interpretation of Reid’s theory leaves him open to several further criticisms. Firstly, it is not clear that visual perception does always proceed through the distinct stages that he describes. However, since the same can also be said of each of the other four senses, this represents a more fundamental problem for Reid’s doctrine of signs than the original charge of inconsistency with respect to direct realism and visual perception. One possible rejoinder would be to claim that the mind proceeds directly to the object signified without any distinct intervening stages whatsoever, although this would conflict with Reid’s official position that perception ‘follows’ sensation and/or visible figure. Of course, it could be argued that Reid was simply wrong about this, in which case the rest of his theory stands relatively unchanged. Another response might be to interpret the distinction between the immediate and intentional objects of perception (in this case visible and actual figure) as delineating functional and cognitive aspects of perception, respectively, rather than constituting a literal description of the mechanism by which perception takes place.11 Indeed, some commentators — notably Immerwahr (1978 in van Cleve 2002) — take Reid to hold just such a ‘double-tier’ theory in which sensation and perception exist alongside one another, or where sensation forms a proper part or ‘element’ of conception and belief (e.g. Pappas op. cit: 163), as opposed to being an interim stage or by-product of the perceptual process. However, again, these interpretations run contrary to Reid’s own writing and so represent a development, rather than a defence, of his account. Perhaps the best response is simply to deny that such processes must take place at the level of conscious awareness, making Reid’s argument an empirical hypothesis about the workings of the human perceptual apparatus.

A second criticism that might be levelled at Reid is that the perception of visible figure as a sign does in fact make visual perception indirect, since it only grants us knowledge of the sign and not of the object, with which we have no direct epistemic contact. However, for Reid, it is not the initial object of perception but the intentional content of the resulting conception and belief that is responsible for the directness of perception. Furthermore, his doctrine of signs explicitly states that one is immediately and non-inferentially followed — and in many cases replaced — by the other at a subsequent stage of the perceptual process. Since intentional content is fixed by the presence of external objects and not just of visible figure, which is a purely relational entity, Reid’s account arguably manages to avoid this objection with respect to visual perception.

VIII. Conclusion

I have argued that Reid’s conception of visible figure does not undermine his direct realism about visual perception on the basis that (i) visible figure is relational, and may be derived mathematically by any rational observer, and (ii) when read in the light of Reid’s overarching ‘doctrine of signs’, the claim that visible figure is the immediate (i.e. initial) object of perception does not affect the directness of visual perception in any important sense. On this account, visible figure is a mere stage or aspect of the perceptual process, rather than an epistemically significant element of Reid’s theory. Furthermore, this often neglected aspect of Reid’s philosophy brings unity to the perceptual faculties by emphasising the role that sensation and visible figure play in the formation of perceptual experience, and the mental processes by which this is supposed to occur. As such, Reid’s treatment of visual perception is consistent with that of the sense modalities of hearing, touch, taste and smell — with the important difference that, unlike sensation, visible figure is both objective and mind-independent. This discrepancy can, however, be put down to genuine phenomenological differences between vision and the other four senses, rather than any inconsistency or oversight on Reid’s part, thus making the above a highly plausible interpretation of his theory of perception as a whole.

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Bibliography

Buras, J. Todd 2002: ‘The Problem with Reid’s Direct Realism’. The Philosophical Quarterly, 52 (209), pp 457–77.

Copenhaver, Rebecca 2000: ‘Thomas Reid’s Direct Realism’. Reid Studies, 4 (1),
pp. 17–34.

—————  2004: ‘A Realism for Reid: Mediated but Direct’. British Journal for the History of Philosophy, 12 (1), pp. 61–74.

Cuneo, Terence & Woudenberg, René (eds.) 2004: The Cambridge Companion to Thomas Reid. Cambridge: Cambridge University Press.

De Rose, Keith 2004: ‘Reid's Anti-Sensationalism and His Realism’. The Philosophical Review, 98 (3), pp. 313–48.

Dummett, Michael 1991: ‘Frege’s Myth of the Third Realm’. In Frege and Other Philosophers. Oxford: Oxford University Press.

Hume, David 1737: A Treatise of Human Nature, Oxford Philosophical Texts Edition, D. F. Norton & M. J. Norton (eds), 2000. Oxford: Oxford University Press.

Immerwahr, J. 1978: ‘The Development of Reid’s Realism’. The Monist, 61 (2),
pp. 245–56.

Malebranche, Nicolas 1688: Dialogues on Metaphysics and Religion. Republished as Dialogues on Metaphysics, W. Doney (trans.), New York: Abaris Books.

McDowell, John 2008: ‘Avoiding the Myth of the Given’. In Experience, Norm and Nature, J. Lindgaard (ed.). Oxford: Blackwell Publishing.

—————  2007: ‘Knowledge and the Space of Reasons’. Unpublished paper given at the University of Stirling, 15/11/2007.

Nichols, Ryan 2002: ‘Visible Figure and Reid's Theory of Visual Perception’. Hume Studies, 28 (1), pp. 49–82.

—————  2007: Thomas Reid’s Theory of Perception. Oxford: Oxford University Press.

Pappas, George S. 1989: ‘Sensation and Perception in Reid’. Noûs, 23 (2), pp. 155–67.

Reid, Thomas 1865: Essays on the Intellectual Powers of Man. London: Charles Griffin and Company.

—————  1997: An Inquiry into the Human Mind on the Principles of Common Sense. Edinburgh: Edinburgh University Press.

Snyder, Allan W. & Miller, William H. 1978: ‘Telephoto Lens System of Falconiform Eyes’. Nature, 275 (5676), pp. 127–9.

Torretti, Roberto 2007: ‘Nineteenth Century Geometry’. In Stanford Encyclopedia of Philosophy. Accessed 13 November 2007, <http://plato.stanford.edu/entries/geometry-19th/#DifGeoRie>.

Van Cleve, James 2002: ‘Thomas Reid’s Geometry of Visibles’. The Philosophical Review, 111 (3), pp. 373–416.

————— 2003: ‘Reid's Theory of Perception’. In The Cambridge Companion to Thomas Reid, pp. 101–33.