Chris Meyns

Publication: The Senses and the History of Philosophy. Edited by Brian R. Glenney and José Filipe Pereira da Silva. London, Routledge, 2019, pp. 169–184.

Summary: Article on Amo's claim, made in response to Descartes, that the human mind cannot sense.

Keywords: perception, Anton Wilhelm Amo, René Descartes, sensation, impassivity

Anton Wilhelm Amo and the Problems of Perception

Anton Wilhelm Amo


“The human mind”, Anton Wilhelm Amo writes at a crucial point in his work on the subject, “is a purely actual and immaterial substance” (1734, p. 4). Amo’s position has serious consequences. Among these is the result that the human mind cannot sense. Instead, he holds that sensation and the faculty of sensing only belong to the body.

Amo (c. 1703–c. 1759) was a legal scholar and natural philosopher working in eighteenth-century Prussia, including at the universities of Halle and Jena. He was among the first African professors in Europe. Representatives of the Dutch West India Company snatched toddler Amo from his home near Axim in Guinea (present-day Ghana), handing him as a “gift” to Duke Anthony Ulrich of Brunswick-Wolfenbüttel in 1707.1 Only two of Amo’s main works are currently extant. He wrote On the Rights of Moors in Europe (De jure Maurorum in Europa, his 1729 law dissertation, presumed lost); On the Impassivity of the Human Mind of 1734, which I will focus on here; and Treatise on the Art of Philosophizing Soberly and Accurately (Tractatus de arte sobrie et accurate philosophandi), a work on logic published in 1738.2 We know Amo lectured on the “most elegant and curious” parts of philosophy, physiognomy, political philosophy, and cryptography (Lochner 1958, p. 177; Abraham 1964, pp. 77–78).

Amo’s radical claim about the mind occurs in his 1734 dissertation, fully titled On the Impassivity of the Human Mind, or How Sensation and the Faculty of Sensing Are Absent from the Human Mind and Present in Our Organic and Living Body (Lat. Dissertatio inauguralis philosophica de humanae mentis ἀπαθεία, seu sensionis ac facultatis sentiendi in mente humana absentia et earum in corpore nostro organico ac vivo praesentia). His stance that the mind cannot sense may sound extreme, but as I will show, he provides valid arguments and starts out from not too unreasonable assumptions. After presenting the structure of Amo’s text and his core concepts, I will discuss his three central theses and how he supports them. This allows me to pin down the exact positive position that Amo ends up with. I discuss three main possible objections to Amo’s views and indicate how he would be able to respond to them. I conclude that while Amo has the resources to resist two main concerns, a final skeptical objection falls outside of the more medically oriented framework in which he operates.

Amo’s project

Amo wrote On the Impassivity of the Human Mind for his doctorate at the University of Wittenberg. He had left the University of Halle, which had come under a spell of conservative pietism under the influence of Johann Joachim Lange (1670–1744), opposing the more progressive, rationalist philosophy of scholars including Christian Thomasius (1655–1728) and Christian Wolff (1679–1754). Wolff was ousted from Halle in 1723, Thomasius died in 1728.

In his dissertation, Amo argues that the human mind does not suffer, have a passion, or undergo anything. In short, he claims that it is impassive—free from all passivity. Amo’s thesis is significant against the background of raving debates between two approaches: a mechanism in the Cartesian–Leibnizian tradition, on which body is strictly separate from the soul, and inanimate matter operates purely mechanically; and vitalist tendencies driven by the work of Georg Ernst Stahl (1660–1734), who held that in living organisms soul animates the body. Amo’s analysis of body and mind as strictly distinct easily makes him side him with the mechanists.

The work has a clear structure. Amo begins Chapter 1 by defining his central concepts, including “spirit” (spiritus), “human mind” (mens humana) (Part I); the predicates of “sensation” (sensio) and “faculty of sensing” (facultas sentiendi) (Part II); and how to understand the condition of “impassivity” (Part III). In Chapter 2 he explains how his central claim splits into three theses, and finally demonstrates what supports each of them.

Mental impassivity

What is the condition of impassivity that Amo says applies to the mind? In his Latin text, he uses the Greek apatheia (ἀπαθεία) untranslated. Apatheia is generally used to indicate a condition opposed to that having pathos (πάθος); that is, a condition without undergoing, feeling or suffering. In this light, it need be no surprise that the concept occurs prominently in the ancient Stoic philosophical tradition, signifying a person’s condition of being free from emotion.3 A further strand lies within the Latin Christian tradition, where apatheia is associated with the doctrine of divine “impassibility,” namely the idea that God is unable to suffer or undergo anything. Following this doctrine, God was understood to be wholly causally independent of anything else. Were God able to suffer they would (impossibly) be subject to another being’s actions.

Against this background, Amo defines impassivity specifically as the absence of sensation. If a being is impassive, it cannot sense and lacks a faculty of sensing (1734, p. 10). What exactly does it come down to for a being to lack sensation in this way? Amo defines “sensation” (sensio) and the faculty of sensing (sentiendi facultas) as, respectively:

  • sensation: Sensation in general is: sensible properties of directly present, material things really acting on the sense organs (1734, pp. 10–11).

  • faculty of sensing: That disposition of our organic and living body, by means of which an animal is affected by material and sensible things and their immediate presence (1734, p. 11).

For example, on this line, the faculty of smelling consists just in the material, living body being so arranged that it is able to register odors when those are present. A sensation of smelling in turn is nothing other than an instance of the sense organs actually being stimulated by the presence of such odors. Hence, Amo analyzes sensation purely in terms of physical stimulation and does not require that sensation must be conscious.

On the surface, Amo’s account may seem to echo some of Leibniz’s statements on unconscious perception. According to Leibniz, we have a bulk of perceptions of which we are not aware. As he states in his New Essays on Human Understanding: “at every moment there is in us an infinity of perceptions, unaccompanied by awareness or reflection” (1996, Preface), though he also notes that we can become conscious of these perceptions if our attention is drawn to them in instances of “apperception” (1996; Leibniz 1969a, sec. 4; Leibniz 1969b, sec. 14).4 Amo agrees that basic processes of sensation do not involve attention. As will become clear, he also accepts that a mind can become aware of sense operations by means of attention. However, his view differs from Leibniz’s on a crucial point. Where Leibniz thinks that unconscious processes of perceiving are always already representations in the soul, Amo captures sensation as a purely corporeal, non-representational process in which no soul or spirit is involved. Hence, despite some similarities, bare sensation fulfills a very different structural role for Amo than it does for Leibniz.

Amo’s definitions clarify that he thinks that sensation involves bodily things, and that whoever senses is in some way being acted upon. Only organic, living bodies disposed in a certain way can have faculties of sensing. Moreover, signaling a broad usage, Amo notes that he also regards what Descartes in Passions of the Soul calls “inner senses” and affections of the soul (animi pathemata) as sensation (1734, p. 11).

The human mind, on Amo’s picture, belongs to the genus of spirit, which is characterized as, “whatever substance is purely actual, immaterial, always understanding through itself”, that is, understanding directly.5 Spirits are conscious and operate spontaneously, by means of intentions or representations of the soul (1734, p. 4). Human minds are distinctive in the category of spirit, because they are those spirits which relate to a living, organic body: “The human mind is: a purely actual and immaterial substance which, in exchange (commercio) with the living and organic body in which it is, understands and operates through intentions, for a purpose and conscious end” (1734, p. 8). In short, Amo sees human minds as immaterial, purely actual, conscious beings that exist in living, organic bodies.

Scholars disagree on how Amo views the relation between mind and body. Jacob Emmanuel Mabe classifies Amo as a defender of a (slightly dubious sounding) “dualistic materialism” (Mabe 2014, p. 76). Both Victor U. Emma-Adamah (2015, p. 156) and Justin E. H. Smith (2015, pp. 223–227) suggest that Amo accepts a pre-established harmony in the spirit of Leibniz. The latter would make contextual sense but is contentious in relation to his text. Amo nowhere cites Leibniz or Wolff in On the Impassivity, nor does he use terms like “harmony,” “concord,” or “correspondence.” Amo’s affinity with a Leibniz–Wolffian mechanism and resistance to vitalism does not settle that he must hold this specific positive position, as a flood of alternative theoretical options on the soul–body relation is equally available. Hence I regard Amo as a (mechanist) dualist and hold off on classifying him as a harmony theorist.

Amo wants to show that an immaterial, actual, conscious being in a living body does not sense. One might think that conclusion follows almost by definition. Amo stipulates that certain beings are “not suited” (non apto) to have sensation, mentioning stones and spirits as examples of such unsuitable subjects (1734, p. 12). Nonetheless, even if the conclusion is within reach, Amo needs to do some work to motivate why this would be so. He does so by specifying his main claim into three theses, two negative and one positive (1734, pp. 15–18):

  • T1. The human mind is not affected by sensible things.

  • T2. There is no faculty of sensing in the human mind.

  • T3. Sensation and the faculty of sensing belong to the body.

He defends each separately.

Support for T1

In support of T1, Amo proposes three proofs. Two of these proofs center around questions of property entailment. In proof 1, Amo argues that sensing entails other attributes that would be incompatible with the soul:

Whatever senses, lives; whatever lives, nourishes; whatever lives and nourishes, grows; whatever exists in this way, is ultimately resolved into its first principle; whatever resolves into its first principle, is a composite (principiatum); each composite has its constitutive parts; whatever exists in this way, is a divisible body; hence if the human mind were to sense, it follows it would be a divisible body. (1734, p. 15)

One might object at several points to this reasoning. Do living and sensing really entail one another? Amo insists so: “To live and to sense are two inseparable predicates” (1734, p. 16). Further, some, such as Thomas Hobbes, will happily accept that all processes traditionally referred to “incorporeal things” are in fact bodily (viz. Leviathan 4.46). Hence, Amo already assumes that the mind is not a divisible body.

In a later proof, Amo attempts a similar line. Drawing on religious authority, he notes that no one needs to fear bodily death because souls cannot perish with the body. From this point, Amo draws out further implications about living, schematically:

  • L1. Whatever can die, lives (ass.).

  • L2. If it lives, then it senses (ass.).

  • L3. If it senses, it enjoys the faculty of sensing (ass.).

  • L4. The body can die (Math. X, 28).

  • L5. The body lives (from L1, L4).

  • L6. The body senses (from L2, L5).

  • L7. The body enjoys the faculty of sensing (from L3, L6).

To establish the soul’s inability to sense, Amo would presumably want to flip the argument around, so that the converse would apply to the soul, as in:

  • L8. The soul cannot die (Math. X, 28).

  • L9. The soul does not live (from L1, L8).

  • L10. The soul does not sense (from L2, L9).

  • L11. The soul does not enjoy the faculty of sensing (from L3, L10).

But, of course, the inference at L9 is invalid, blocking steps L10–L11. Nothing in L1 settles how the property of living relates to the inability to die. Something unable to die might just as well live forever.

The most significant support for T1 comes when Amo (in Proof 2) postulates a general exclusion, writing, “No spirit senses material things; and yet the human mind is a Spirit, therefore it does not sense material things” (1734, p. 15). Formally:

  • S1. Spirit does not sense material things.

  • S2. The human mind is a spirit.

  • S3. The human mind does not sense material things.

As Amo takes S2 as an instance of genus-species classification, he holds that it does not allow for contradiction (1734, pp. 15–16). The major S1, however, is a different story. Amo feels he has already supported it in his earlier definition of spirit. Updating the argument for completeness, it would look as follows:

  • Sʹ1. Spirit is purely actual (ass.).

  • Sʹ2. Whatever is purely actual does admit passion (ass.).

  • Sʹ3. Spirit does not admit passion (from Sʹ1, Sʹ2).

  • Sʹ4. To admit passion is to sense material things (ass.).

  • Sʹ5. Spirit does not sense material things (from Sʹ3, Sʹ4).

  • Sʹ6. The human mind is a spirit (ass.).

  • Sʹ7. The human mind does not sense material things (from Sʹ5, Sʹ6).

Here, Sʹ1 is simply Amo’s definition of spirit. I have supplied Sʹ2 and Sʹ4, making explicit the reasoning and the work Amo wants the argument to do. Sʹ4 should be fine if passion (or passivity) and sensation are equivalents, as Amo thinks. He seeks to demonstrate the mind’s impassivity by showing that a mind cannot have sensation. In the background here is that Amo has defined “sensation” as a condition in which material things operate on the sense organ (1734, pp. 10–11) and where being operated on is a passive relation.

Point Sʹ2 should not be too controversial. For any set of opposites, if something is wholly A, then it cannot also simultaneously be wholly not-A. Something 100-percent waterproof cannot at the same time be 40-percent leaky. Hence, if we understand passivity as potentiality and assume that potentiality opposes actuality, then whatever is fully actual cannot also at the same time be to a certain extent non-actual, as Sʹ2 states. Hence, here Amo demonstrates the human mind’s incapacity to sense.6 Surprisingly, even though he has already inferred it, he subsequently offers an additional proof of point Sʹ5. His reasoning is insightful about his wider picture of sense perception.

Amo’s demonstrates Sʹ5 by elimination. If a spirit were to have passion, that would have to happen either by communication, or by penetration, or through contact (1734, p. 5). But if none of these options works, then spirit cannot have passion. Let’s take communication first. Amo defines communication as “The extent to which the Parts, properties and effects of one being, by means of some act, come to be present in another being analogously and aptly” (1734, p. 5). For example, when I warm my hands near the fire, the heat of fire gets communicated (transfers) from the fire to my hands. Spirits cannot have this, Amo argues:

No parts, properties and other effects of a being can come to be present in a spirit by means of some act; otherwise spirit would contain in its essence and substance something other than what it ought to contain. Likewise, to contain, and to be contained are material concepts, which cannot truly be predicated of spirit. Therefore spirit does not sense by communication. (1734, p. 5)

Through communication, spirit would come to contain something of another substance in itself; a part, property or effect. But spirits, which we presume are simple, cannot contain extrinsic things. The whole notion of the containment (continere) is only applicable to material things, which spirit is not.

Pushing ahead, Amo adds that sensible beings and spirits are “contrary opposites” (contrarie oppositae): they are comparable, but the one lacks a defining property which the other has (e.g., material and nonmaterial) (1734, p. 8). No contrary opposites can communicate. Hence, communication thrice fails for spirits.

Similarly, spirits have passion by penetration, in which parts of one being transfer to another, Amo notes (1734, p. 5). Spirits cannot be penetrated, because spirits do not have parts: “No spirit senses or is affected by way of penetration, because penetration is: The transition of a being through parts of another being; but no spirit enjoys constitutive parts; Therefore; [spirit] is beyond all passion” (1734, p. 6). Here too Amo relies on definitions, namely of spirit as unitary. If spirits indeed lack parts, they cannot be penetrated.

Amo’s reasoning on part-free spirits reflects early modern and medieval debates. Just two decades prior, Leibniz, in Monadology (1969b), insisted that spirits are partless because they are not material and that whatever lacks parts cannot be acted upon. After introducing the monad as “a simple substance … without parts” (Leibniz 1969b, sec. 1), Leibniz notes:

There is also no way of explaining how a Monad can be altered or changed in its inner being by any other created thing, since there is no possibility of transposition within it, nor can we conceive of any internal movement which can be produced, directed, increased or diminished there within the substance, such as can take place in the case of composites where a change can occur among the parts. (Leibniz 1969b, sec. 7)

If partless substances cannot be changed by being acted upon, then they must be their own principles of activity. While Amo does not cite Leibniz, he draws on similar arguments in resisting the idea that minds could be penetrated.

Finally, spirit could not sense through contact (contactum). Amo describes contact as: “The extent to which two surfaces in some physical or sensible point in some way mutually touch” (1734, p. 5). Contact by definition involves touch. As Descartes had shown—Amo cites Descartes’ correspondence with Elisabeth of Bohemia—touch is a characteristic only applicable to body (1734, p. 6). Spirit is not body, hence spirit cannot touch, and so not be in contact with anything. In this argument, as in others, Amo mobilizes a basic incompatibility between spirit and body. He does not present it as a brute fact because he offers wider considerations (about opposites, parts, contact), but it does stand out as a core premise.

With no option remaining for spirit to sense, that completes Amo’s additional proof of claim Sʹ5 that spirit lacks sensation. These three proofs settle Thesis 1, that the human mind does not sense. Amo’s support for T2 and T3 is more succinct.

Support for T2

For T2, Amo offers just a single proof, which again considers the intertwinement between various properties: “To that to which the circulation of the blood belongs, to that also belongs the principle of life; and to which this belongs, also belongs the faculty of sensing; Anyway, the circulation of the blood & the principle of life belong to the body” (1734, p. 17).

Amo must assume these options to be exclusive and exhaustive, such that sensing (living, blood circulation) must belong either to body or to mind but not to both, and so if it belongs to the body, it cannot belong to the mind. This support for T2 is relevant because it shows how Amo backs up his reasoning with the medical science of his time, explicitly referring to several recent texts in physiology (Johann Gottfried Berger’s Physiologia, 1702; and Christian Vater’s Physiologia experimentalis, 1712).

Support for T3

Amo’s proof of T3, brief and relying on prior results, finally explicates the direct exclusion principle that already surfaced earlier: “Sensation and the faculty of sensing belong either to the mind, or to the body, not to the mind, as has been extensively deduced. Therefore [they belong] to the body” (1734, p. 18).

With those points in hand, Amo has offered support for all three theses (T1–T3) of his central claim that the human mind is impassive. What positive picture of the mind results?

Active mind

The human mind, as far as Amo is concerned, does not sense. Rather, mind operates fully spontaneously and uses the body as an instrument in its operations. Amo states that spirit is: “always understanding through itself, and operates spontaneously with intention, for a purpose and conscious end (conscium finem)” (1734, p. 4), and, later, “Every spirit operates spontaneously i.e. intrinsically determines its operations toward an end to be pursued, nor is it in any other way forced to operate” (1734, p. 7). How do we know that spirit operates spontaneously? We know this, because:

If spirit were forced by another, this would happen either with another spirit or matter forcing. If another spirit, that preserves in both the spontaneity or the faculty to freely act and react. If spirit were forced by matter, it would not be able to, because spirit is always actual, while matter is always something undergoing (patiens), and receiving all action operating upon it. (1734, p. 7)

Matter is always passive, says Amo, therein following a long tradition reaching back through medieval philosophy all the way to ancient Greece. If matter is always passive, then it cannot act upon things—spirit included. Surprisingly, Amo seems to allow that spirit could force (act upon) another spirit. Though he immediately suggests that if one spirit were to force another, it would still not detract from neither spirit’s spontaneous operation. My shot is that Amo thinks that any spirit would still have to perform those “forced” acts itself, from its own intentions. Hence even a forced spirit would still be operating spontaneously. This analysis has implications for the relation between the human mind and its organic, living body.

Amo suggests that the human mind uses the body as its “instrument” or “medium,” using sensations occurring in the body. That Amo allows a form of mind–body exchange may sound surprising, as he strongly denies that a body could act upon the soul. But we can make sense of such interactions as asymmetric relations. Exchanges need not be two-way things: “Exchange of body and mind consists in this (1) it [sc. the human mind] uses the body in which it is as subject (2) as instrument and medium of its operations” (1734, p. 8).

In explaining (T1), Amo had said of the human mind that it understands and uses sensations appearing in the body (1734, p. 15). We can then conceive of the full process as follows:

  • Stage 1: Sensible things are present to the body, stimulating the sense organs.

  • Stage 2: The soul attends to the sensory organ as it is stimulated and commences its own operation.

The process of sensation itself, presented here as Stage 1, does not involve the soul nor any instances of attending. Were we to put it in terms of conscious or unconscious processes, then whatever happens at Stage 1 is not conscious. Stage 2, however, does involve processes that could classify as “conscious,” in so far as it involves the soul’s acts of attending. Stage 1 involves the purely corporeal, mechanical process of sensation, whereas Stage 2 is initiated spontaneously by the mind. Crucially, this requires no extrinsic properties to transfer into, or be contained in, spirit. All it requires is the soul’s attention and subsequent spontaneous action. Amo insists that mind and body still remain strictly separate in any such exchange:

Likewise we there do not confuse the diverse aspects of the body and the mind coming together. For whatever consists in the pure operation of the mind, is to be attributed only to the mind; whatever truly presupposes sensation, the faculty of sensing, and concepts involving matter, is all to be attributed to the body. (1734, p. 18)

When I use my phone to communicate or determine my location, I nonetheless remain distinct from it. Similarly, a mind that uses a body as an instrument still remains distinct from it. Sensation and the faculty of sensing belong to the body, while the mind operates spontaneously. With Amo’s reasoning out there, I will consider several points of pushback that it might face. For example, Amo’s definition of sensing as passive was central to one of his proofs of T1 but can be challenged from a strand of thinking about sense perception as active.

Pushback 1: Active sensing

Plotinus (c. 205–270) insisted that perception is an act of mind: “Perceptions are no imprints, we have said, are not to be thought of as seal-impressions on soul or mind,” continuing that, instead, “[t]he mind affirms something not contained within it: this is precisely the characteristic of a power—not to accept impression but, within its allotted sphere, to act” (Plotinus 1966, book IV, ch. 6, sec. 1, 2). Similarly, Augustine (354–430) writes about a case of seeing a body:

[L]et us remember how these three things, although diverse in nature, are tempered together into a kind of unity; that is, the form of the body which is seen, and the image of it impressed on the sense, which is vision or sense informed, and the will of the mind which applies the sense to the sensible thing, and retains the vision itself in it. […] But the third is of the soul alone, because it is the will. (Augustine 2002, 11.5)

Perceiving, for Augustine, is never simply a case of objects passively impressing something on the soul. It also always involves an act of the soul itself.7 Similar considerations about how perception must involve an active element come up in Themistius (317–390), Simplicius (c. 490–c. 560), Boethius (c. 480–524), Averroes (1126–1198), and Nicholas of Cusa (1401–1464), among many others.8

Why accept a theory of active perception? One reason lies in metaphysics. Augustine and others assumed a metaphysical hierarchy, where causation only flows in one direction: the ontologically nobler can act upon the ontologically less noble, not the other way around (except by a mode of resistance). As immaterial spirits are assumed to be metaphysically nobler than body, body must be assumed to be unable to act upon spirit.9

Even Descartes, to whom Amo regularly refers, is a candidate for a theorist of active perception, but for different reasons. In his sixth set of replies to objections to his Meditations, Descartes distinguishes three grades of perception. The first grade concerns purely corporeal stimulation by external objects, the second “everything that immediately results in the mind on account of its being united to the bodily organ that is affected,” such as bodily feelings, emotion, sensation. Of the final grade, Descartes states: “The third grade includes all the judgments that, on the occasion of motions in the bodily organs, we have been accustomed to make since childhood about things existing outside us” (Descartes 1964–1976, vol. VII, p. 437). Judging is an act, hence Cartesian perception is at least to this extent active.10

Descartes had distinguished grades of perception in response to Marin Mersenne’s (1588–1648) charge that—contrary to Descartes’s claims—the senses are actually more reliable than the intellect. Distinguishing these grades of perception allows Descartes to pinpoint the risk of error in the perceptual process. Perceptual Grades 1 and 2 are error-free: “For it is clear that we are not dealing here with the first and second levels of sensation, because there can be no falsity in them” (Descartes 1964–1976, vol. VII, p. 438). In Grade 3, however, we are active and can make (or fix) mistakes: “And therefore this very example shows that only the intellect can correct the errors of the senses; nor can any example be found of error due to trusting the operations of the mind rather than the senses” (Descartes 1964–1976, vol. VII, p. 439). To explain the possibility of perceptual error, Descartes resorts to active perception.11

This brings up two reasons for accepting sense perception as active. One, with Augustine and others, the consideration that body is metaphysically less noble than spirit, and so—assuming associated restrictions on causation—would not be able to act upon spirit. Since spirit still perceives, its perception must be its own act. Another epistemical, as discussed for Descartes, where distinguishing an active stage of perception can help to account for the possibility of perceptual error. While passive “effects” of sensory stimulation cannot be erroneous, our perceptual judgments may slip. Would either of these concerns put pressure on Amo?

Amo need not be moved by either argument. First, Amo’s work contains remarkable parallels with Neoplatonist ideas about metaphysical hierarchy. While Amo does not invoke the doctrine that spirit would be metaphysically nobler than the body, his insistence on the soul’s impassivity ties in with this idea, as well as with the later religious doctrine that God cannot be acted upon or suffer from the actions of another being. Further, Amo even agrees with authors in that tradition on aspects of process: bodily sense organs are stimulated, the souls acts of itself. However, he parts ways with the tradition on classification. While Plotinus and Augustine see the act of the soul as sense perception, Amo insists that sensation is restricted to the stimulation of corporeal sense organs. Without further criteria of what a theory of sense perception must explain, either party could insist that they capture the process correctly—giving either a more inclusive or a more minimalist account of the process. Hence, Amo need feel no pressure to expand his classification of “sensing” to include acts of mind.

Similarly for the epistemic point. Amo could endorse elements of Descartes’s grades of perception. He agrees that material things stimulate the sense organ (Descartes’ Grade 1). He also accepts that the soul acts (Grade 3). But he denies that anything—feelings, emotions, sensation—could be produced in the mind as a direct result of its attachment to the body (Grade 2). Because it would amount to an instance of the mind being (impossibly) passive and acted upon, Amo denies that anything takes place of the kind that Descartes captures as Grade 2 of perception. Sure, the mind can be in a variety of contentful states. However, on his analysis, no state of the mind will ever be directly caused by the body’s operation.

Descartes sought to differentiate between grades of perception to explain the possibility of perceptual error. Could Amo accommodate the possibility of error with a different overall analysis? Were he so inclined, he could explain error as resulting from the mind’s own, active judgments. He would simply deny that this would be sense perception.

Even Descartes seems flexible on the exact source of perceptual error, attributing the third grade of “perception” solely to intellect. After discussing how a stick half-immersed in water looks crooked, Descartes notes (Descartes 1964–1976, vol. VII, pp. 437–438):

For when I judge, from this sensation of colour by which I am affected, that the stick, existing outside me, is coloured, and when I estimate its size, shape, and distance from the extension and the boundaries of this colour and from the relation of its position to the parts of the brain, even though these activities are commonly ascribed to the senses, for which reason I included them here in the third level of sensation, it is nonetheless clear that they depend on the intellect alone.

If acknowledging the mind’s activity suffices for explaining possible error, then whether one classifies this process as “perception” (as Descartes does) or not (as Amo would have it) does not make any argumentative difference. Hence, Amo also has the means to resist this pressure to broaden the category of sensation on epistemic grounds.

While this settles the first pushback, more aspects of Amo’s work can be challenged. How about his assumption that spirit is purely actual?

Pushback 2: Spiritual passion

In Passions of the Soul (1649), Descartes had stated that the mind can be acted upon, or have passions. In one of his broader definitions, he notes: In the first place, I note that whatever takes place or occurs is generally called by philosophers a “passion” with regard to the subject to which it happens and an “action” with regard to that which makes it happen. Thus, although an agent and patient are often quite different, an action and passion must always be a single thing which has these two names on account of the two different subjects to which it may be related. (Descartes 1964–1976, vol. IX, p. 328)

On that line, any occurrence necessarily always has two dimensions—active and passive—but classifies as “action” or “passion” depending on how it is considered. An occurrence is an action for whatever caused it (which for Descartes could be the mind itself, or something external to the mind), but a passion for the subject in or to which it occurs. When you kick me, I am kicked. The same event is a kicking on your part (the agent) and a getting-kicked for me (the one subject to it). Hence, the occurrence is at once an action (as far as you are concerned) and a passion (for me).

Elsewhere, Descartes provides a stricter account of passions, classifying passions as “perceptions” (that is, as “modes of knowledge” or representations) with a specific cause, namely “we may define them generally as those perceptions, sensations or emotions of the soul which we refer particularly to it, and which are caused, maintained and strengthened by some movements of the spirits” (Descartes 1964–1976, vol. IX, p. 349). Here Descartes builds upon his distinction between three different kinds (not grades) of perceptions, based on what they are “referred” to,that is, what we judge them to be caused by (Descartes 1964–1976, vol. IX, pp. 345–348):

  • External sensations: perceptions caused by objects outside us.

  • Internal sensations: perceptions caused by the natural appetites of our body.

  • Passions: perceptions caused by our soul

In this narrow sense, passions, for Descartes, are those perceptions that we judge to be caused by the soul and “whose effects we feel as being in the soul itself” (Descartes 1964–1976, vol IX, p. 347).

What Descartes says about passions need not worry Amo, for two reasons. For one thing, while Descartes presents an overview, he omits any argument for why his inventory of states of the soul is correct. Without such argument, Amo can simply offer a different inventory, leaving the two authors argumentatively on a par—Descartes allowing passion in the mind, Amo resisting it.

More significantly, Amo could pick up on Descartes’s admission that his “passion” of the soul, those perceptions we refer to the soul itself, “is really one and the same thing as a volition” (Descartes 1964–1976, vol. IX, p. 343). Volitions are actions of the soul. Amo could insist that if an act is performed by the soul, it must count not as a passion but as an action of the soul. As though anticipating such a concern, Descartes explicates that these perceptions are best captured as passions because ultimately we passively perceive this act of willing:

And although willing something is an action with respect to our soul, the perception of such willing may be said to be a passion in the soul. But because this perception is really one and the same thing as a volition, and names are always determined by whatever is most noble, we do not normally call it a ‘passion’, but solely an ‘action’. (Descartes 1964–1976, vol. IX, p. 343)

In short, Descartes falls back on conventional classification when insisting that the soul has passions. Amo has addressed part of Descartes’ stance when discussing whether a spirit’s spontaneous action could be compromised by an external force. He ruled this out because any external force would still be forcing the soul’s spontaneous action. This suggests that Amo takes it as a general rule that whatever occurs in a spirit is a spontaneous action of that spirit. Hence, what Descartes classifies as the soul’s passions, Amo would still understand as a mental act.

Amo may here be pushing back against a Cartesian strict separation between intellect and will. Where Descartes allows intellect as receptive (passive apprehension) and will as active (judgment, involving assent), Amo brings these two closer together, attributing any reflection to an act of mind. This is a disagreement, of course. But it is not one that can be decided in either party’s favor without further criteria or evidence.

Pushback 3: Epistemic risk

Here is a final, still more serious, issue. Some, including Descartes, have given the passivity of sensation an argumentative role in demonstrating the existence of body (Descartes 1964–1976, vol. VII, pp. 79–80). When, in Meditation VI, Descartes describes all of his sensations, he insists that he cannot but have these sensory ideas:

And surely it was not without reason that, on account of the ideas of all these qualities that presented themselves to my thought, and of which alone I had personal and immediate sensations, I believed I was sensing certain things quite distinct from my thought, that is to say, bodies from which these ideas proceeded. For I experienced these ideas as coming to me without any consent of mine. (Descartes 1964–1976, vol. VII, p. 75)

We can reconstruct Descartes’s claim and subsequent proof of the existence of body (AT VII 79–80) as follows:

  • PB1. Sensible ideas are produced either by me or by something other than me (ass.).

  • PB2. If sensible ideas were produced by me, they would not occur against my will (ass.).

  • PB3. Sensible ideas do occur against my will (ass.).

  • PB4. Sensible ideas are not produced by me (from PB2, PB3).

  • PB5. Sensible ideas are produced by something other than me (from PB1, PB4).

  • PB6. If sensible ideas are produced by something other than me, they are produced either by god, or by body (ass.).

  • PB7. Sensible ideas are produced either by God, or by body (from PB5, PB6).

  • PB8. If sensible ideas were produce in me by god, then they would come from something which does not formally12 contain the objective reality of these ideas (ass.).

  • PB9. If sensible ideas would were produced by something which does not formally contain the objective reality of these ideas, then god would be a deceiver (ass.).

  • PB10. God is no deceiver (ass.).

  • PB11. Sensible ideas are not produced by something which does not formally contain the objective reality of these ideas (from PB9, PB10).

  • PB12. Sensible ideas are not produced by god (from PB8, PB11).

  • PB13. Sensible ideas are produced by body (from PB7, PB12).

  • PB14. If sensible ideas are produced by body, then body exists (ass).

  • PB15. Body exist (from PB13, PB14).

Descartes uses the observation that I do not produce certain of my sensory ideas to argue for the conclusion that bodily things exist. Bodies’ causal effect on my cognition affirms their existence. If I did produce all of my ideas, as Amo insists, then this proof of the existence of bodily things would not go through.

Amo would likely want to resist PB3, that sensible ideas occur against my will, or against the soul’s action. Indeed, he would be happy to accept that sensible things—light, sounds, odors, flavors, or tactile properties—can stimulate a body’s sense organs unsolicited. However, none of those processes of corporeal stimulation amounts to the soul’s having ideas against its will. This is because the soul on Amo’s picture only experiences when it attends, and attending is not something that unwittingly happens to the soul; it is the soul’s own action.

Amo has urged that spirit operates spontaneously, that is, through its own intentions, and that it determines its operations (1734, pp. 7–8), including the operation of attending to what occurs in the body. But the dialectic is murky here. If spirit indeed operates spontaneously, then that contradicts Descartes’s supposed “datum” in PB3 that sensible ideas can occur against my will. And if PB3 is to be given up, none of the inferences depending on it can go through either.

Consider two main issues. First, if the soul does not sense, and hence receives no confirmation of the existence of body through being causally affected by body, can Amo demonstrate that body exists in some other way? While Amo defines the human mind as being “in” a living, organic body, nothing he has said so far rules out that (at least epistemically) this corporeal instrument and its user could be detached from one another. Second, if sensory ideas are spontaneously self-produced, does cognition on Amo’s model still in any way latch onto corporeal things in the world? Or would it float freely in epistemic isolation?

Amo can avoid a risk of epistemic isolation. Yes, he argues that spirit operates spontaneously. But spontaneous thought need not be baseless. Amo says that the mind uses bodily sensations as an instrument or medium (1734, p. 8). Elaborating on T1, he notes, “the human mind is not affected by sensible things, although they are closely present to the body in which it is; But it understands sensations appearing in the body, and uses [these] understandings in its operations” (1734, p. 15). As sketched, a possible account of the “exchange” Amo envisages would have it that sensible things operate on the body while the soul attends to the stimulation and commences its own operation. Only with the mind’s attending is there a conscious awareness. On this picture, the mind’s spontaneous acts are produced while using what happens in the body. Bodily stimulation does not cause the mind’s operation. Rather, it provides the mind an occasion to operate. Instruments—be they forks, phones, or bodies—can be useful even if they do not cause their user to operate. If the mind uses corporeal stimulation as its starting point in spontaneous action, then that case of instrument use circumvents the risk of cognition ending up free-floating, severed from corporeality.

Things are different for the proof of the existence of body. Amo gladly accepts that there is such a thing as body. He directly refers to body, and requires it in his analysis of sensation in T3. All the same, it looks like Amo is not too concerned about wider metaphysical or skeptical questions about body’s existence. Instead, within the context of his dissertation, he regards such questions either as settled, or as no suitable object of his own philosophical inquiries.

Indirect support for this diagnosis lies in the debates that Amo orients himself toward, which are mostly physiological. He rejects the Wittenbergian physician and chemist Daniel Sennert’s (1572–1637) view that the mind senses, discusses Jean Leclerc’s (1657–1736) treatise of spirit (Pneumatologia, 1710), and references work by the surgeon Georg Daniel Coschwitz (1679–1729), a follower of Stahl’s vitalism. When Amo cites Descartes, he focuses on questions about perception, not on broader metaphysical doubts. Amo ventures into topics of physiology, but his comments on the wider physics of, say, visual perception (optics) are limited. Given this, he seems unconcerned to refute a skeptic about the existence of body but silently presumes these issues dealt with.


Anton Wilhelm Amo offers the radical stance that the human mind cannot have sense perception, as defended in On the Impassivity of the Human Mind. Zooming in on Amo’s three main theses—(T1) that the human mind does not sense; (T2) that the human mind does not have a faculty of sensing; and (T3) that sense perception belongs to the body, I have shown that much of his reasoning relies on assumptions that spirit must be purely active and that spirit excludes anything bodily. Amo radicalizes the Cartesian separation of spirit and body, ending up with a causal asymmetry: while no body can act upon mind, minds can use bodies as instruments in their operation. Around these ideas Amo builds his arguments that the human mind does not sense, and only ever acts spontaneously.

Within the wider early modern perception debate, Amo can expect several lines of pushback, of which I here considered three: (1) Could perception be active? (2) Could passivity be realized in spirit? and (3) Does spontaneous cognition carry substantial epistemic risk? Amo has the material to ward off most these challenges. On (1), he broadly agrees with active perception theorists on matters of process (a sense organ gets stimulated, the mind is active), but has grounds to resist classifying the mind’s activity as “perception.” On (2), he can insist that there is insufficient evidence to conclude that the mind experiences its own acts passively; all we know for sure is simply that the mind itself acts. On issues of epistemic risk, (3), Amo’s results are mixed. While he can resist any concerns about spontaneously operating minds ending up “free-floating” from corporeality, skeptical issues about the very existence of body will draw a blank. Perhaps that need not be a major issue. Immersed in early eighteenth-century physiological approaches to sense perception, Amo has at this point simply stepped away from a wider skeptical framework that might underpin such worries.


  1. Facts about Amo’s life are scarce and sometimes disputed. Biographical notes on Amo can be found in: Lochner (1958); Abraham (1964, 2008); Brentjes (1976); Bess (1989); and Sephocle (1992). As Houtondji (1996) and Damis (2002) correctly note, much of the literature has “instrumentalized” Amo, focusing mainly on his extraordinary life while ignoring his actual work. Change is on its way, though, with more studies recently touching on Amo’s philosophy of mind, including Hountondji (1996), Wiredu (2004), Mabe (2014), Smith (2015),and Emma-Adamah (2015).

  2. A text by Johannes Theodosius Meiner (1734), which Amo supervised, is sometimes also attributed to Amo.

  3. Apatheia is discussed as the absence of emotion in persons by, among others, Zeno of Citium, Dionysius of Heraclea, Democritus (as reported in Diogenes Laërtius 1925, book VII, pp. 110, 167, book IX, p. 45), and in Epictetus’s Discourses (Epictetus 1768, book 4, ch. 6).

  4. See: Kulstad (1981, 1991); McRae (1976); Theil (1994); and Jorgensen (2009, 2011) for canonical discussions of Leibniz on grades of perception and apperception.

  5. Hountondji has argued that Amo’s claim that the human mind uses the body for cognition “is tantamount to saying that the human mind cannot be regarded as a particular species of the genus spirit” (1996, p. 125). As will become clear below, this is incorrect. Hence here I will stick to Amo’s classification.

  6. Wiredu (2004, pp. 203–205) surprisingly states that Amo’s discussion of activity and passivity adds nothing to his argument against Descartes. Instead, they propose that with this move Amo may idiosyncratically have been pushing influences of the Akan thought that he would have been exposed to as a three-year-old toddler. However, Wiredu misrepresents aspects of Descartes position and ignores how concerns about active and passive perception build upon a long Aristotelian–scholastic tradition in which Amo would have received formal instruction. Taking that into account, we can see how, in using arguments about activity and passivity, Amo is in no way idiosyncratic but builds upon a received body of thought.

  7. For more on Plotinus on perception see Blumenthal (1971) and Emilsson (1988); for Augustine, O’Daly (1987, chapters 3–5) and Byers (2012) provide extended studies.

  8. See Pasnau (1997, chapter 4), Spruit (2008), and Silva and Yrjönsuuri (2014) for studies on active perception in medieval and early modern debates.

  9. Silva describes Augustine’s stance on metaphysical nobility as follows: “the soul’s activity guarantees the inviolability of the basic ontological principles of the superiority of the soul over the body” (2014, p. 117). See also Leijenhorst (2014, p. 169), and Menn (2002, p. 153).

  10. Descartes’s stance on active perception has recently been taken up by Wee (2014) as well as in Leijenhorst (2014, pp. 179–180).

  11. Casting Descartes as a theorist of active perception may be surprising, as he regularly emphasizes perception’s passivity: “Moreover, there is in me a certain passive faculty of sensation, that is, of receiving and knowing ideas of sensible things” (Descartes 1964–1976, vol. VII, p. 79). However, while grades 1–2 stand out as mere “effects” on the sense organs and in turn the soul, his claims in the Sixth Replies signal that these only account for part of the perceptual process.

  12. Following scholastic terminology, formal containment is something’s belonging to a thing’s form or nature (essence). It contrasts with objective containment (having it in the mind) or for Descartes in this passage with eminent containment (designating how everything are contained in God).


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