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ABSTRACT
Descartes analysed the mind into various faculties or powers, including pure intellect, imagination, senses, and will. This article focuses on his account of the sensory power, in relation to its Aristotelian background. Descartes accepted from the Aristotelians that the senses serve to preserve the body by detecting benefits and harms. He rejected the scholastic Aristotelian sensory ontology of resembling species, or ‘forms without matter’. For the visual sense, Descartes offered a mechanistic ontology and a partially mechanized account of sensory processes, including some previously ascribed to judgement. He did this in the context of his theory of brain signs that prompt sensations. The article contends that Descartes’s use of the sign-relation was modelled on standard discussions of non-resembling signs in commentaries on Aristotle’s De interpretatione. It follows three uses of the sign-relation: brain states that cause colour sensations; brain states that cause experiences of spatialized contents, such as shapes; and brain states that realize a ‘natural geometry’. It argues that Descartes’s natural geometry does not involve mental operations but physiological mechanisms that co-vary with the distance to seen objects. While retaining the language of sensory powers, Descartes offered a partial mechanization of those powers.
Notes
1 Descartes’s works are cited in the Adam and Tannery edition, abbreviated ‘AT’, with volume and page numbers; the Principles and Passions, by Part and article numbers. Specific works are mentioned using abbreviated English titles; citations to volume 7 are the Meditations. The translations are my own.
2 This paragraph characterizes types of cognition that Descartes says are useful for knowing things or representing them cognitively. Descartes’s usage of the terms scientia (knowledge; science), cognitio (cognition; knowledge), cogitatio (thought), perceptio (perception), sensus (sensation; sense organ), and related terms is not easily systematized nor even well understood. On the supposition that he demands certainty for knowledge, he nonetheless allows that some thoughts, cognitions, perceptions, and even sensations can be cognitively useful in the absence of certainty, as with the ‘teachings of nature’ from the Sixth Meditation (7: 80–3). Although an act of will is required for a judgement (Fourth Meditation) and hence for a potential act of knowledge, Descartes allows that bare sensory ideas have representational content that may or may not match reality, and that may result in a judgement or not – for example, instead resulting in a motivation to act to avoid something fearful (7: 37). Herein, I mention ‘perceptions’ that are not instances of perceptual knowledge but sense-perceptual representations, which may or may not enter into further acts of judgement but nonetheless are assessable for representational accuracy. See Hatfield, Meditations, xx–xxi, 154–63, 273–4.
3 On powers of the soul in medieval philosophy: (Haldane, ‘Soul and Body’) and (Hasse, ‘Soul’s Faculties’); on Aristotelians around 1600: (Hatfield, ‘Mechanizing’).
4 Des Chene (Spirits, Chap. 2–3) discusses the interplay between structure and function in Descartes’s sketchy account of the formation of the sense organs (Description, 11: 261–4) and finds that, more generally, many structures persist in the developing machine because they yield a stable animal body (Spirits, 58–9). The interplay between function and finality in Descartes is intricate (see also Hatfield, ‘Animals’).
5 Historians disagree on whether Descartes’s human body is individuated by its organic unity or gains identity only in relation to mind. Simmons (‘Re-Humanizing’, 63) has identity and functional integrity depend on mind–body union; Manning (‘Descartes’ Machines’) has identity depend on God’s intentions in the Treatise and on our considering the body as a machine in the Meditations; Hatfield (‘Animals’, 416–17) makes functional unity arise from the body’s ‘nature’, a natural philosophical notion that does not establish metaphysical unity. Even if the body gains identity in relation to mind, it still has a mechanical structure to which the mind is adjusted, as when God adjusts mind–body interaction to the bodily ‘machine’ (Sixth Meditation, 7: 84–8).
6 Descartes’s correspondence with Elisabeth in 1643 concludes that we do not clearly understand mind–body union and interaction but that, in the act of sense perception, we become aware that it exists (AT 3: 692–4). Passions (I.1–2) provides no metaphysical insights but describes functional relations (which are frequently invoked in the work). The present article does not address whether Descartes accepted interactionism or some form of body–mind occasionalism.
7 Ariew (Descartes) and Gaukroger (Descartes, Chap. 2) offer differing accounts of Descartes’s relation to his intellectual background. See also Hatfield (Meditations, Chap. 1). It is uncontroversial that Descartes adopted elements from Aristotelianism, if only some basic terms and concepts; herein, I find more continuity than usual, along with deep differences.
8 Schmitt (Aristotle) offers a limited survey, favouring natural philosophy. Spruit (Species intelligibilis) traces the Aristotelian concept of intelligible species from antiquity to the early modern period (hence, including metaphysics), selectively surveying the Renaissance and seventeenth century in the lengthy second volume. Gilson (Index) tracks Descartes’s relations mainly to the authors named later in this paragraph.
9 On Descartes and contemporary Scotists, including Eustachius, see Ariew (Descartes).
10 This claim remains true, despite verbal similarities and partial precedents in some scholastic authors (Des Chene, ‘Aristotelian Natural Philosophy’). Of course, the details matter more if one asks which scholastic ideas Descartes may have adapted to his own purposes. But he sees himself as opposing a generic Aristotelianism.
11 As needed, I cite translations of Aquinas, Eustachius, and others, and the Latin texts of the Conimbricenses and Toledo; and I give secondary sources that cite in detail the primary texts of our Aristotelian authors. I also cite Descartes’s texts describing Aristotelian tenets.
12 On the sensitive power of the soul and the five senses, see THN (Qu. 78, art. 4). For additional primary sources (including our target authors and medical authors Descartes knew), see Hatfield (‘Mechanizing’, 157–61). On ‘forms without matter’ in the medium (for vision), see Hatfield (‘Cognitive Faculties’, 956). Of course, other Aristotelians (outside our core group) denied sensible species (Spruit, Species intelligibilis, 1: 292–3, 2: 319).
13 Other Aristotelian internal senses include imagination and memory (Hatfield, ‘Mechanizing’, 160–3). As noted, Descartes used the term ‘internal sense’ not for these capacities but for bodily appetites and passions. In the Aristotelian scheme, sensory appetite, which gives rise to passions or emotions, is distinct from the internal senses.
14 Broader and narrower senses of the term ‘intentional’ need be distinguished in this period. Broadly, all sensible species are ‘intentional’, which has two connotations: (1) a species of colour does not render the air or eye coloured as it passes through them, because it has diminished or merely ‘intentional’ being; (2) the species directs the senses toward the coloured surface or represents it (Hatfield, ‘Cognitive Faculties’, 956–8). More narrowly, the term applies only to properties discerned exclusively by the internal senses (so, for vision, properties beyond colour and shape), as the estimative power discerns the enmity of the wolf; such ‘intentions’ are distinguished from ‘sensible forms’ received by the senses (THN, Qu. 78, art. 4; see Hasse, ‘Soul’s Faculties’, 308–9, 314–16). Descartes employs the broader usage (AT 6: 85).
15 Those Aristotelian theories of sense perception that posited the reception of a sensible form without matter typically considered this form, or species, to be a ‘likeness’ or ‘similitude’ (similitudo) of the quality of colour in the object (THN Qu. 78, art. 1, 3). Descartes uses French ‘semblable’ or ‘resemblance’ (AT 6: 112–14) for similar or resembling entities; in Latin, ‘similis’ or ‘similitudo’ (7: 38), the same words used by the scholastics. Some scholars have him interpret the scholastics as establishing a phenomenal resemblance between colour experiences and coloured things via a mental projection of the experiences onto the things (for discussion, Pasnau, Metaphysical Themes, 493–5). More likely, Descartes correctly understood the form or similitude of colour as being received in the sense organ and sensory power via intentional species (Hatfield, ‘Cognitive Faculties’, 957–9); he then denied that any such similitude or species is transmitted and received. See also Simmons (‘Explaining Sense Perception’).
16 Kepler first described the formation of a true optical image in the eye, on the retina (Lindberg, Theories of Vision, 202). But prior perspectivist theories posited two-dimensional patterns of sensation that are appropriately called images (Hatfield and Epstein, ‘Sensory Core’, 369–73).
17 I use ‘institution’ and cognates to translate the French and Latin terms ‘institution’ and ‘institutum’, as found in the phrases ‘institution de la nature’, ‘ex humano instituto’, and ‘par l’institution des hommes’; also in the definition of ‘naturale’ as ‘Quod Naturae primae institutionem & ordinem sequitur’ (Goclenius, Lexicon, 744). This translation can be awkward, but it reveals a shared vocabulary that is masked by renderings such as ‘established by nature’ or ‘human convention’.
18 ‘Force’ and ‘character’ ultimately describe animal spirits flowing from the pineal gland. Flowing spirits and images formed on a ‘certain small gland’ are mentioned in the Dioptrics (6: 110–12, 129), but the details are given in the Treatise (11: 129, 174–88).
19 Translation emended from Read’s (‘Concepts and Meaning’, 14–15) rendering of Boethius’ Latin; Read surveys the reception of Boethius’ discussion in medieval Latin commentaries.
20 Bolton (‘Confused and Obscure’) and Simmons (‘Cartesian Sensations’) contend that colour sensations (and other sensory qualities) represent object properties. Hatfield (‘Descartes on Sensory Representation’) argues that colour sensations obscurely represent (by resemblance) the micro-features of surfaces, while constituting a manifest experience of colour that is non-resembling and surface-presenting. The argument herein does not depend on these positions. One might treat sensations as blank signs; the brain sign would yield a non-intentional qualitative sensation, the sign-value of which would be learned, as with a ‘sign through habit’ in the Aristotelian scheme.
21 See Chap. 22 in Gaukroger et al., Descartes’ Natural Philosophy, responding to Yolton, Perceptual Acquaintance, Chap. 11; also, Chignell, ‘Descartes on Sensation’.
22 Descartes expects his reader to be familiar with words as arbitrary signs (‘You well know’) – perhaps from the commentaries on De Interpretatione.
23 Chignell (‘Descartes on Sensation’) has the mind taking a hermeneutic stance toward brain states, being ‘aware of’ and ‘inspecting’ them in a homuncular manner. Some passages suggest this; for a non-homuncular reading, see Hatfield (‘Seeing Distance’, 178, n. 22). Chignell’s position requires that the mind possess innately a hermeneutics for interpreting brain states and perceiving distant objects via them. I find it simpler to suppose that the mind is innately constituted such that specific brain states produce specific sensations (as suggested in Dioptrics VI).
24 Descartes’s physiological psychology is built on a sensorimotor interplay involving a central brain cavity and animal spirits (subtle matter) that flow from the pineal gland. The cavity is composed of nerve tubules such that, when they are opened through sensory stimulation (via filaments inside the tubules), animal spirits flow to the openings. With voluntary motor acts and acts of imagination, the mind directs patterns of spirits, which force open the appropriate tubules. For the basics, see Des Chene (Spirits, Chap. 4) or Hatfield (‘Mechanizing’, 167–81). Descartes has this physiology in mind in discussing the ‘machine’ of the human body and sensory nerves as ‘cords’ in the Sixth Meditation (AT 7: 84–5, 87).
25 (Graham, ‘Intellect’s Burden’) provides an overview.
26 In the Treatise, Descartes uses the term ‘idea’ for purely corporeal states that will, in an ensouled human, cause sense perceptions or other experiences (11: 177).
27 The Dioptrics adumbrates a view found in later authors, that in accommodation the shape of the whole eye is altered, presumably via the extraocular muscles (6: 116–17, 137); the Treatise posits mechanisms within the eye that change the shape of the lens (11: 153).
28 Descartes does not specifically address the perception of various distances within the field of view (off the point of convergence), but the Treatise (11: 157–8) suggests that successive fixations are conjoined to form the perception of a three-dimensional scene (which he might have envisioned as produced psychophysiologically). As noted below, Descartes also has the perception of distance (three dimensions) arise through habitual mental processes.
29 For human vision, Descartes has a hybrid psychophysiological and judgemental account of size, shape, and distance perception, with psychophysiology dominating for near distances (Hatfield, ‘Natural Geometry’, Sec. 9).
30 Thanks for helpful comments on earlier versions presented at the South-Central Seminar in Early Modern Philosophy, Texas A&M University, and the Summer School on Epistemology and Cognition, University of Groningen, and from the co-editors of this issue and the anonymous referees.