Amo and Molyneux’s Question

An article that discusses what the philosopher Anton Amo (ca. 1703–ca. 1750) plausibly might have said, had they considered questions about cross-modal learning


Counterfactual history of philosophy is part of history of philosophy, which in turn belongs to the enterprise of historical explanation.When doing history, as Geoffrey Hawthorn points out:

[U]nderstanding possibility is at the heart of understanding itself. Although this is in a sense a theoretical issue, no theory, I suggest, can resolve it. Answers to questions about humanly plausible worlds … are given by judgement, in particular, by practical judgement. And the resources that we need to make such judgements, I argue, are given in the details of particular cases. (Hawthorn 1993: xi)

By inquiring into alternative philosophical histories that are plausible, as opposed to merely possible, we are not just explaining, but also aiming to increase understanding of the cases at hand (contrast this with the verdict that reflection on what might have been is a mere “parlour game”; Carr 1964: 97).

The “particular case” for which I will here tease out the plausible from the not-so-plausible is a conversation between two philosophers that did not happen. One which, moreover, could not have happened, given that one of its projected participants was deceased before the other was born. It is a hypothetical which may nonetheless offer us increased insight into the philosophical commitments of one of the parties involved.

On 2 March 1693 the Dublin based William Molyneux (1656–1698)—who was rich from inherited wealth and so at leisure to pursue matters of interest, such as writing on optics, politics and constitutional matters, as well as contributing papers to the journal of the newly founded Royal Society of London—wrote to his friend John Locke about an at that point still counterfactual case (having previously raised the issue in 1688 without receiving a reply):

Suppose a Man born blind, and now adult, and taught by his Touch to distinguish between a Cube and a Sphere (suppose) of Ivory, nighly of the seme Bigness, so as to tell when he felt one and t’other, which is the Cube, which the Sphere; suppose then the Cube and Sphere plac’d on a Table, and the blind Man to be made to see; Query, whether by his Sight, before he touch’d them, he could now distinguish and tell which is the Globe, which the Cube? (Locke 1742: 31–32)

Technically, the query Molyneux posed to his companion comprises a matter for experimental investigation in what would now be called neuroscience and has, over the centuries, indeed regularly been taken up in that field. Nonetheless, Locke found the matter worth speculating upon, and he included it in the second edition of his Essay Concerning Human Understanding (published in 1694), the work which had initially prompted Molyneux’s thought, thus disseminating the puzzle to a wider audience. Subsequent philosophers have regularly taken up the question, and their answers (yes or no) have often been seen as revealing how that author thought about the nature of cognition in relation to sense perception.

The natural philosopher and legal scholar Anton Wilhelm Amo (ca. 1703–ca. 1750), who worked at the universities of Wittenberg and Halle and is known chiefly for his two major works On the Impassivity of the Human Mind (1734) and Treatise on the Art of Philosophising Soberly and Accurately (1738), is not among those who took up Molyneux’s ask.

While there was a general interest in Locke’s theories in Germany from the early eighteenth century onward—including from authors such as Otto Mencke (1644–1707), Gottfried Leibniz (1646–1716), Christian Thomasius (1655–1728), and Christian Wolff (1679–1754)—and a full Latin version of Locke’s Essay was first available in Germany 1710—nonetheless there is little indication that Molyneux’s question specifically had much uptake here (Brown 1951: 467, 474, 476–77). True, Leibniz engaged with the question in his New Essays on Human Understanding written in response to Locke, but while finished in 1704, this text was only published in the 1760s (well after Amo’s death). One of the few documents at the time discussing Locke and Molyneux together—the oration given by Johann Christoph Gottsched (1700–1766, an influential German literary critic) on the occasion of his appointment as a professor of logic and metaphysics at Leipzig—does not touch on Molyneux’s question, or any other philosophical matters, at all (Gottsched, 1734). Titled, in translation, The injustice of foreigners in the judgement concerning our erudites, confirmed with the example of the illustrious men Jo[hn] Locke and Wilh[elm] Molyneux, it makes for a glorious piece of scholarship-cum-nationalist-propaganda, complaining how “arrogant and scornful people” from abroad had discussed German authors unfairly. More importantly, nothing in Amo’s writing indicates that he ever contemplated the question Molyneux posed to Locke.

Still, in the spirit of investigating the counterfactually plausible about what Amo might have responded to Molyneux, I suggest we can get greater insight into Amo’s philosophical commitments, in particular regarding sensation and cognition.

One reason why Amo’s work is, I suggest, fruitfully read with the issue that Molyneux posed in mind is that, based on our still nascent understanding of Amo’s work, his commitments seem to pull in divergent directions. On the one hand Amo is often thought to align with an author who was squarely in the camp of a “Yes” answer. Indeed, various scholars have argued that one of Amo’s central claims—namely that the mind does not sense, but is impassive—places him close to views held by Leibniz (Emma-Adamah 2015:156; Smith 2015: 23). Leibniz, voiced by his spokesperson Theophilus, did respond to Molyneux’s question:

The question strikes me as a rather interesting one. I would need to spend time thinking about it; but since you urge me to reply at once I will risk saying, just between the two of us, that I believe that if the blind man knows that the two shapes which he sees are those of a cube and a sphere, he will be able to identify them and to say without touching them that this one is the sphere and this the cube. (Leibniz 1996: II.ix.8)

On the other hand, some of Amo’s work, especially on the nature of ideas, shows significant affinities with the work of Locke who, in agreement with his chum Molyneux, was adamant on a “No” response. Molyneux stated that a newly sighted person would not be able to distinguish a globe from a cube merely by sight:

… for though he has obtained the Experience of how a Globe, how a Cube affects his Touch, yet he has not yet attain’d the Experience, that what affects his Touch so or so, must affect his Sight so or so; or that a protuberant Angle in the Cube, that press’d his Hand unequally, shall appear to his Eye as it does in the Cube. (Locke 1742: 32)

On which Locke comments that this answer seems to him “acute and judicious” (Locke 1975: II.ix.9)

Would Amo’s commitment to impassivity push him to accept, with Leibniz, that a person newly sighted would indeed be able to distinguish the two geometrical shapes? Or would his affinities with Locke’s manner of thinking about ideas push him in the completely opposite direction?

Here I will argue that there are good grounds for holding the latter view—that Amo would respond with a negative to Molyneux’s question—to be most counterfactual-historically plausible. I will support this diagnosis as follows. In section two I set out the core elements of Amo’s philosophy of mind, followed in section three with a reframing of Molyneux’s query into Amo’s philosophical framework. I then, in section four, run through three distinct options for how Amo might have thought that a newly sighted person can cognitively achieve a recognition, such that a “Yes” answer could be supported. Each of these three options fails, and so I conclude that there is most ground for inferring that Amo would have answered that no, a person newly sighted would not be able to distinguish the two shapes just by sight. In section five, I specify what this hypothetical answer shows us about Amo’s broader philosophical commitments.

Amo’s commitments on cognition and sensation

The three central philosophical ideas that will be relevant when confronting Amo’s system with Molyneux’s question are the following: first, the claim that the human mind is impassive (that is, it does not sense); second, the idea that sensation belongs only to the organic, living body; and third, that the mind itself can nonetheless use its organic, living body as an instrument in its operations. Let me clarify these points.

Commitment 1: The human mind is impassive

A human mind, Amo states, is:

… a purely actual and immaterial substance which, in exchange with the living and organic body in which it belongs, understands and operates from intentions to an end of which it is self-conscious. (Amo 1734: 8)

Two points are crucial here. One is that Amo holds that the mind is an immaterial (or: spiritual) substance. Specifically, he says that it is, among other things, not just immaterial but also conscious (conscium), it operates spontaneously, is purposive or end-directed and, most importantly for what Amo wants to argue, a mind is purely actual and so admits no potentiality or passivity of any sort (Amo 1734: 4).

The other main point is that Amo sees the human mind as distinctive in the genus of spirit, because it has “exchange” (commercio) with a living, organic and material body (Amo 1734: 8) (while Amo sees material and immaterial things as mutually exclusive, at the same time he regards mind and body as the two essential parts of a human being; Amo 1734: 6, 8–9).

Amo’s account of the mind resembles that of Descartes, who also captured the mind as an immaterial, thinking thing. However, where Descartes is wont to refer to the soul’s “passions” (Descartes 1964–1976, vol. VII: 75, 79–80, 437; vol. IX: 328, 343, 347, 349), one of Amo’s most distinctive philosophical theses is that “against Descartes [contra Cartesium]” he maintains that the human mind cannot and does not have any form of passivity (Amo, 1734: 13).This, for him, includes sense perception. Amo thinks that the human mind cannot sense. It can only think.

Amo calls the human mind’s incapacity for sensing its “impassivity” (Gr. apatheia [ἀπαθεία], which Amo leaves untranslated in his Latin text). For Amo, impassivity is not simply the general idea of lacking pathos (πάθος), that is, of not undergoing any feeling or suffering (although he does sometimes note that “I have shown that spirit does not sense or suffer”, for instance at Amo 1734: 6). Rather, he captures impassivity more specifically as the absence of sensation. If a mind is impassive, that means it cannot sense and lacks a faculty of sensing:

What impassivity (apatheia, ἀπαθεία) of the human mind [is] … namely: absence of a faculty of sensing and immediate sensations in the human mind. (Amo 1738: 13, cf. 1734: 4, 10, 13)

Amo offers a variety of arguments for why it must be that minds cannot sense, the most crucial ones of which I will discuss in detail.A linchpin is his observation that a spirit is immaterial and purely active, from which Amo infers: “No spirit senses material things; and yet the human mind is a Spirit, therefore it does not sense material things” (Amo 1734, p. 15) (for discussions of Amo’s arguments for impassivity, as well as his wider philosophy, see: Lochner 1958;Abraham 1964, 2004; Brentjes 1969, 1975, 1976; Fikes 1980; Bess 1989; Sephocle 1992; Hountondji 1996; Bemile 2002; Damis 2002; Wiredu 2004; Mabe 2007; Mougnol 2010; Emma-Adamah 2015; Smith 2015; Oppong 2017; Meyns 2019a, 2019b; Walsh, 2019).

One might think that one would simply draw a “Yes” answer—that is, the conclusion that Amo would think that yes, a person who has just acquired sight would be able to distinguish a sphere from a cube just by looking—directly from Amo’s impassivity thesis. Amo claims that the mind is impassive, and that it itself does not sense. Hence, whatever happens in the mind cannot but be a spontaneous, self-initiated act of that mind. This may, initially, lead one to think that Amo must think that all ideas (which are, after all, operations of that mind) can draw upon nothing but the mind which has them. Hence, also ideas of geometric shape cannot be acquired through stimulation of one or more different sense modalities, but must ultimately be solely the product of the mind’s own spontaneous, modality-independent operations. If that is the case, then—as per Molyneux’s query—any supposed access to one sense modality (vision) as opposed to another (touch) should not be expected to make much of a difference. After all, it would be the same, modality-independent ideas of geometric shape that the mind would operate with. If a switch from one to the other would not make any difference, and presuming the person set to the task would already be able to apply ideas of shape, then Amo might be thought to say that they would still be able to do so even when drawing on vision as opposed to touch.

However, such an inference based purely on Amo’s impassivity thesis cannot work. It cannot work, because it would disregard a core other element of his philosophy, namely his assumption of a sensory basis of cognition.Amo repeatedly insists that nothing is in the intellect which was not previously in the senses. Indeed, he holds that the mind is impassive and cannot sense. But he also sees that mind as associated with a body, a body which senses, and a body which the mind uses, and must use, in thinking about the world. If (or insofar as) Amo does claim that the mind derives all its ideas from sensation, then we simply cannot assume that ideas of 3D geometric shape would be generally available to the mind without being bound to a specific sense modality. This brings me to Amo’s second and third major philosophical commitments, concerning the nature and basis of sensation.

Commitment 2: Sensation belongs to the organic, living body

In his 1734 Impassivity, Amo captures sensation (Lat. sensio) as the process in which “sensible properties of immediately present, material things really act against the sense organs” (Amo 1734, pp. 10–11). That is, Amo views sensing as the basic process of stimulation of the bodily sense organs; in short, a purely corporeal matter. A faculty of sensing, in turn, is “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” (Amo 1734: 11). (Note that Amo says that he uses “sensation”, “sensing” (sensius) and “sense” (sensio) synonymously; Amo 1734: 11).

That approach persists in his Treatise of 1738, where he says: “Sensation (sensio) in general is: the sensible properties of immediately present, material things really operating upon the sense organs” (Amo 1738: 10–11). He calls the faculty of sensing “a disposition of our organic and living body, by means of which the living being is affected by immediately present things” (Amo 1738: 11). Amo’s argument for his conclusion draws on a simple exclusion principle:

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. (Amo 1734: 18)

Precisely because Amo thinks that the mind (being a spirit) does not sense, he maintains that both sensation and the faculty of sensing must be purely corporeal matters (in this verdict Amo stays close to physiological traditions of his time, including works by Johan Gottfried Berger (1659–1736), Christian Vater (1651–1732), Daniel Sennert (1572–1637), Georg Daniel Coschwitz (1679–1729), all of whom he cites). But what, if all of this is the case, can then be made of the relation of “exchange” between mind and body which Amo thought was so distinctive of human minds?

Commitment 3: The mind can use its organic, living body as an instrument

The third of Amo’s central commitments relevant for ascertaining his position on Molyneux’s question concerns the relation between mind and body. Specifically, Amo thinks that human minds are associated with organic, living bodies. This association will prove theoretically crucial. For Amo supposes that it is precisely because of such a connection that the human mind can use (utatur) the body in which it seeks to perform its operations. As he states:

Exchange of body and mind consists in these that (1) it [the human mind] uses the body in which it is as a subject (2) as an instrument and medium of its operations. (Amo 1734: 8)

Later on, Amo specifies that the mind can issue an “effective act of mind” (actus mentis effectivus) in conjunction with the body, where such effective acts are instances of thinking (Amo 1738: 45; cf. Meiner 1734: 5, 10). Amo calls an “idea” an “… operation of our mind, by which it represents or makes present to itself things previously perceived with the senses and sensory organs” (Amo 1734: 7, 15).

What, concretely, does this come down to? Amo emphasises the mind’s representational character, or in short, that the mind thinks with ideas:

That in us which represents to itself is called mind [mens]; that, with which it instrumentally represents other things to itself, [is called] its representative act; that which it represents to itself as an object, is sense, of which something remains in the sense organs or [in] memory; For nothing is in the intellect which was not previously in the senses. The way in which sense is represented to the mind, is called an idea. (Amo 1738: 58)

Take an example. Say that the skin of my hands touches an ivory globe in front of me. Amo holds that this physical sensation establishes in me what he calls an “archetype” (Lat. archetypo), by which he roughly means the referent of an idea. Tactile qualities of the ivory stimulate my skin; its smoothness, temperature, the density as I press it. The human mind, being connected with the body, can in turn attend to what happens in the sense organs and so use this archetype in its mental operations of thinking about—that is, of having ideas of, or representing—these tactile qualities. Hence, the mind can use the body with which it is connected, and in particular the purely physical sensation taking place thence, to obtain ideas and think of things in the world.

Amo is not keen to restrict the scope of his claim regarding a sensory basis of ideas; instead, he envisages a sensory basis for all cognition. He regularly makes the point that: “Nothing is in the intellect, which had not previously been in the senses” (Amo 1738: 63, cf. 59, 62, 70, 83).1 He describes remaining sensation as “a physical adjunct” (adiunctum physicum) which the intellect uses in its operations of thinking and knowing things, and notes that all the mind’s representations spring from the sensing body (Amo 1738: 42–43, 70).

Both Amo’s claim that nothing is in the intellect which was not previously in the senses, as well as the notion of an archetype, echo Locke’s work, who had written that the mind is “furnished” with ideas through sensation (Locke 1975: II.i.2); and who equally used the notion of an archetype to indicate the referent of an idea (Locke 1975: II.xxxi.4). While Amo does not cite Locke, he does frequently refer to the work of Jean Leclerc (1657–1736) who was an early translator and good friend of Locke’s, and whose own philosophy was significantly influenced by the latter’s theories (Leclerc 1700).

Is Amo’s claim that the mind can use its body as an instrument in any way in conflict with his earlier statement that the mind is impassive? Amo does not think so. For if the mind uses the body in its thinking, that is still an operation that the mind itself performs. It is not an instance where it suffers or is acted upon. What Amo allows is a one-directional, asymmetric “exchange” running from mind to body, never from body to mind. The body is acted upon through purely physical sensory stimulation; the mind attends to such stimulation as it occurs in the bodily sense organs, but all it does arises out of its own spontaneous action. Hence (so Amo would say) the sensory basis of the mind’s ideas is perfectly consistent with the mind’s overall impassivity.

Molyneux’s query in Amo’s framework

Molyneux’s query contained a number of specifications that could be significant for Amo’s hypothetical answer, as I will describe in what follows. First, Molyneux asked about an act of distinguishing, in querying the reader whether the person could “distinguish and tell which is the Globe, which the Cube?” (italics added for emphasis). Amo describes distinction as an act: “… in which the mind considers predicates which are not sufficiently determinate”, in particular the extent to which, if at all, the predicate is contained in the subject (Amo 1738: 141).

Amo views distinction as a post-reflective (post reflexionem) intellectual operation: it is one in which the mind is in some way concerned with the existence, origin and nature of things, as opposed to what he calls “pre-reflective” acts in which the mind merely apprehends ideas, which he calls “instantaneous” or “momentary” (momentaneus) (Amo 1738: 46–47, 83ff, 141). Hence, distinction for Amo concerns a judgement about predicates, and the extent to which they apply to a thing.

Second, Molyneux is concerned with distinguishing two objects directly confronting the person making the distinction, with respect to their geometric shapes. Amo identifies a core limitation at this point.He holds that things as such (or,in his terminology,“substances”) cannot be thought of by the mind, but only their qualities, if and insofar as these are sensible. As he states: “The mind is unable to represent a thing as such [secundum se] but only the properties & qualities of a thing that are perceptible to & perceived by the senses” (Amo 1738: 59). As well as:“Therefore [it] does not represent a thing itself to itself but the sensible qualities of things &c to the extent that they are sensible” (Amo 1738: 59–60). Amo ridicules that if things as such— absent sensible qualities—could be represented, then “… it would follow, that the mind would be able to represent to itself Spirit as such, which is impossible” (Amo 1738: 59).

Note that Amo is not claiming that things cannot be represented (and hence thought of) at all. After all, representing “the properties & qualities of a thing”, as he mentions, would be a way of representing that thing—if only indirectly. But he even goes further by indicating how the mind could come to have ideas of more abstract things which (we suppose) would not ordinarily be able to operate on the sense organs.Amo suggests that reflection, and in particular contemplative reflective acts, enable a mind to think ideas such as that of God, spirit, the human mind, matter, properties, parts, ideas of morals and politics (Amo 1738: 95).2 Hence, distinction between two objects, as Molyneux asked for, for Amo in the first instance comes down to a distinction between the sensible qualities that we are able to perceive from those objects.

Third, Molyneux places a methodological restriction, namely that in making their distinction, the person draws only on the sense of vision (which they have newly acquired) and not on any other senses (which they, we presume, are well familiar with).

Amo touches on a distinction between what we would now call sense modalities when he discusses degrees of clarity in ideas.Amo sees differences in degrees of clarity and obscurity as a foundation for dividing sensory ideas; which, in turn, can be seen as strategy for differentiating between the senses that facilitate these ideas.

Working with a traditional list of senses—namely vision, audition, olfaction, taste, and touch—Amo produces an hierarchical ordering in which one sense “surpasses” another in its degree of clarity and subtlety (or, conversely, its obscurity and density) (Amo 1738: 76). (An idea of a thing is “obscure”, according to Amo, when we cannot determine all of the parts and properties of what the idea is of, and “clear” where this is possible; Amo 1738: 74–75).

By induction, he deems vision to be most clear and subtle. He simply notes: “That degree of clarity & subtlety, with which vision surpasses audition, to that degree audition [surpasses] olfaction, olfaction taste, [and] taste touch”, and: “The highest degree of clarity are those, which are perceived by vision” (Amo 1738: 76, cf. 77). By contrast, Amo is much more hesitant about what can be obtained from touch. He states: “That degree of obscurity & density with which touch surpasses taste, to that same degree taste [surpasses] olfaction, olfaction audition, audition vision.” (Amo 1738: 76). Just to make things absolutely clear, he notes: “The perceptibles of touch have maximum obscurity” (Amo 1738: 76). Of all the senses, then, Amo thinks of vision as clearest and touch as most obscure (there is a precedent for such pessimism about touch: Aristotle in his study of the senses, too, complains that “… we are unable clearly to detect in the case of touch what the single subject is which corresponds to sound in the case of hearing” De Anima, 422b32).

Some comment might be in order on what Amo’s stance on the distinction between the senses really comes down to. Does he regard clarity and obscurity as the basis for distinguishing sense modalities? Or is he giving a quantified account, purely in terms of how many properties each sense is able to pick up on? Exciting as these options might be, I suggest there is good reason to think that Amo’s position on sense modalities would actually be rather more mundane. Yes, he thinks that the senses differ in the relative degree of obscurity of their ideas; where obscurity is captured in terms of the range of properties it can capture. And yes, he even thinks that one can give an ordinal ranking in terms of this relative clarity: vision ranking as clearest, followed by audition, olfaction, taste and lastly touch. However, nothing suggests that Amo would see these characteristics of relative clarity and obscurity as the basis for a distinction between several sense modalities (instead of seeing them as simply characterising sense modalities that are already distinct on a different basis). At this point it would be wise to recall the third ofAmo’s core philosophical commitments,namely sensation’s bodily basis. A physical body will have various physical sensory organs which the mind is able to use as its instrument. He has called the sensation remaining in the sense organ the “foundation” of sensory ideas (Amo 1738: 71). All this makes it not implausible that Amo would envisage sensory modalities as distinct based on something as basic as which corporeal tool was used to generate them—with which in turn a grasp of different properties, and varying degrees of clarity and obscurity, are associated.

If all of this is correct, then it follows that Amo would see the case that Molyneux poses as one in which a person would be allowed to draw on the sense which can provide the clearest ideas (but which they had not used before) and is no longer able to use a sense which offers nothing but ideas with maximum obscurity (but which to them would be familiar).With this framing in place, what might we expect Amo to respond to Molyneux’s question?

What might Amo respond to Molyneux’s question?

As has been discussed, it will not be possible simply to infer Amo’s hypothetical response to Molyneux’s question directly from his impassivity thesis, as such an inference would have to ignore his other major philosophical commitments regarding the nature and bodily basis of sensation.That being assumed, what then might Amo’s stance on the question be?

Option 1: Vision gives us figure directly

Here is a more interpretively sound reason for thinking that Amo might respond to Molyneux with a “Yes” answer: not only has Amo claimed that vision is the clearest sense, more strongly, in making that point, he expressly states that one of the properties of a thing that vision can pick up on or, in his words, “accurately determine & enumerate”, is that of “figure” (figuram) (Amo 1738: 76) (together with a list of no fewer than 24 other properties accessible to vision, ranging from olour, quality, quantity, and relation to time, place,as well as motion and rest; Amo 1738: 76. The large number of properties available to vision, in contrast with the lower number of properties that touch might detect, is Amo’s basis for classifying the former sense as clearer and the latter as more obscure). If the sense of vision can accurately determine the figure properties of a thing, one would expect that to include also the figures of being cubical or spherical, possessed by the two objects that Molyneux’s test subject is said to be confronted with. In which case, there is every reason to think that they could positively distinguish by sight alone which of the two objects has which shape (or figure).

However, this line of reasoning faces a complication. Amo, when noting which properties vision can give us ideas of, spoke of sight quite generally. But the case that Molyneux laid out is one where it is the very first time that a newly sighted person will be operating their visual sense organs. There is no reason to assume that what someone would be able to do once they are familiar with operating their sight would automatically extend to an exceptional case like this one. Or, more precisely, we cannot assume that Amo would have extended what he says about the general case to the circumstance of using a new sense for the first time.

What in addition may raise doubts are certain further statements that Amo makes—not so much about which properties vision gives us access to, but rather about the domain of mathematical (and hence geometric) thought. Amo states that mathematical thought is a habit:

Mathematics is: A cognitive habit & effective intention, where we consider determinations & proportions of determinable things as such & with respect to measurement. The end of it broadly appears to be what can be determined. (Amo 1738: 19)

Habits, for Amo and many others around this period, are accidental properties; they are “not as such and originally in a thing” on which they are predicated in the way essential properties might be—for example, how horseness belongs to a horse, or thinking to a spirit—but rather, they are acquired. Or, as Amo specifies: “Habitual is: Readiness acquired [through] frequently repeated exercise; & properly it is called habit [habitus]” (Amo 1738: 38).

Habits are acquired through repeated, regular exercise. If geometric thought is a habit, then it too must be acquired through repeated exercise. Unfortunately, Amo nowhere provides a general theory of (sensory) learning, development or skill acquisition. But what we do know is that in the situation that Molyneux sketches, the person uses their sense of vision for the very first time. If something is used for the very first time, then it cannot at the same time also be a repeated usage. Hence, if and insofar as geometric thought was a habit specific to ideas of the sense of vision, then the newly sighted person could not already have that habit. If the person does not already have that habit, then they equally will not at that point be able to exercise it. And if they cannot, in these circumstances, exercise a habit of geometric thought, then any of their attempts to distinguish between the shapes of a cube and a sphere they are confronted with would be no better than random. Hence, if this were the case, then Molyneux’s question would have to be answered in the negative.

Of course, we need not give up here. Might there be other ways in which Amo could envisage a person newly sighted to have a habit of geometric thought that would be available to them when confronting two differently shaped objects in vision for the first time? In what follows I will consider two additional alternatives. One is that the person had acquired a habit of geometric thought in a way that was not, in fact, bound to any particular sense modality (a generalised, amodal thought) (discussed here as Option 2). The other (Option 3) is that the person obtained a habit of geometric thought specific to the sense modality in which it was acquired (any sense but vision) but is, through some form of translation between ideas, nonetheless able to draw upon that pre-existing habit in their newly acquired sight.

Option 2: Ideas of shape are not tied to a particular sense modality

Given that Amo himself already notes that the mind can have ideas of imperceptibles—including ideas of spirit, justice, mind and morals—he might plausibly be open to the idea that mental operations could provide us with habits of thought that are not tied to specific sense modalities. Amo might here think of operations such as reflection or contemplation, as discussed, or for instance of abstraction. Amo captures abstraction as a mental operation in which we consider the individual parts or properties of things separately (Amo 1738: 67). Such mental operations could result in more general, modality-independent ideas and habits of thinking mathematically.

Leibniz, in the voice of his spokesperson Theophilus, considered a similar approach when concluding that “… it seems to me past question” that someone could distinguish between two geometric shapes using purely their newly acquired sense of vision (Leibniz 1996: II.ix.8). What a person in that situation needs to be able to draw on, Leibniz says, is what he calls an “exact idea” of shape (which he contrasts with “images“. And “exact ideas”, Leibniz says, “are composed of definitions” (Leibniz 1996: II.ix.8). If someone has available to them an exact idea, or definition, of what a cube and a sphere are, and they would be able to extrapolate “by applying rational principles to the sensory knowledge which [that person] has already acquired by touch” (Leibniz 1996: II.ix.8), then, Leibniz holds, they would be able to differentiate the two shapes correctly.3

Amo, for his part, indeed makes much of the mind’s capacity of working with definitions, where he calls a definition a “[d]eterminate & adequate cognition of a thing, declared with distinct and perspicuous words” (Amo 1738: 24); and discusses definition at length in his Treatise.

A newly sighted person might, for example, have previously encountered Euclid’s “distinct and perspicuous words” that a cube is “a solid figure contained by six equal squares” (Euclid 1845: bk XI, def. 25), and that a sphere as “a solid figure described by the revolution of a semicircle about its diameter, which remains unmoved” (Euclid 1845: bk XI, def. 14).4 Euclid’s definitions of a cube and a sphere make reference to spatial concepts—solids, figures, squares, positions and diameters. They do not, however, include reference to specific sensory modalities within which those spatial units must be encountered. Depending on one’s training or familiarity, one might be able to identify a spatial position by touch, hearing or visually. In short, Euclid’s definitions could provide the exact geometric ideas on which Leibniz based his “Yes” answer. Would Amo reckon that, with definitions such as these in hand, a person who newly acquired sight would be able to distinguish a cube from a sphere simply by looking (and inferring)?

While promising, that conclusion actually turns out to be unlikely for Amo. Plausibly, Amo would agree that with a definition such as Euclid’s, someone could have a “determinate and adequate cognition” of the relevant geometric shapes that is not bound to any particular sense modality (other than the manner in which the words of the definitions would be communicated—which, in the eighteenth century, for a person with vision impairment would most likely be auditory, as night writing and Braille were only developed a century later).

Nonetheless, issues arise when turning to Amo’s view of what sort of mental operation would be involved in the act of mind that constitutes thinking definitions. And at this point Amo suggests that, even for exact, abstract thought, the actual thinking still cannot but operate with representations of past sensations in one or more of the person’s particular sensory modalities. For example, in his discussion of definition, Amo specifies that in terms of what the mind does, definition should be understood as: “A representative act of mind, where it intentionally expresses to itself each and every sensation and idea representing a thing denominated” (Amo 1738: 133). Statements may be exact and abstract—not so, according to Amo, our cognition. Cognitively, the act of thinking definitions is still the repetition of past sensations.

In fact, Amo had already made a similar point when discussing ideas of incorporeal things. While on the one hand he noted that: “In thinking therefore of spirits and incorporeal things, we must beware not to confuse the idea with that which is thought or the archetype, for the idea is in this way corporeal, that which is thought of indeed incorporeal” (Amo 1738: 63), at the same time he says: “… [there is] no intellection & idea without an archetype perceptible to the senses” (Amo 1738: 63).

If any actual thinking of definitions must still draw on ideas from individual sense modalities, that has implications for someone who has only worked with hearing, smell, touch, or taste, and now adds to that vision for the first time. For it means that the sense and representations that they would be able to revive—and which, in turn, their cognition would be tied up with— could up to this point only be revived sensations from one of the sense modalities they were already familiar with; in the case of geometric thought, that would most likely be touch or audition. Hence, when this person actually thinks of a solid figure contained by six equal squares, or of a semicircle with a fixed diameter being carried round, their actual thinking will represent sensations obtained from touch, or possibly hearing. There is no reason to think that Amo would suppose that they could simply extrapolate from those to match whatever sensations are at that moment coming in through vision. Hence, even in the case of abstract, definitional thought, we cannot assume that Amo would expect the newly sighted person to correctly distinguish between the two objects.

Option 3: Ideas of vision could translate into ideas of touch

Or could we? Might Amo have envisaged, after all, some manner of “translating” ideas tied to one sense modality directly into ideas associated with another sense? Could habits of geometric thought acquired through one form of sensory stimulation expand into another?

Initially, there does actually seem to be a case for attributing a thought along these lines to Amo. In the course of demonstrating that vision is the clearest sense, Amo considers whether ideas of properties associated with one sense could be “lead back” (reducuntur) to those of another sense. Deciding positively, he gives examples of how perceptibles of other senses could be traced to those of vision:

Many [of the] remaining things perceived with the senses, become clearer to the intellect when brought back to the sense of vision. Thus e.g. with the benefit of watches time is lead back to the sense of vision; elementary qualities perceived by touch [are so returned] with barometers & thermometers; no less holds for audible things, which we see musical notations, which exhibit musical tones. (Amo 1738: 76–77)

If Amo thinks that tactile and audible qualities can be led back to—that is, represented in—a manner accessible to vision, does that not signal that he sees opportunities for translating directly from one sense modality to the other?

That is not obvious. For look closely at what precisely Amo claims here. Consider the barometer case, which would be an example of properties accessible to touch being brought back to (translated into) properties accessible to vision. To use a barometer, you do not need to be familiar with registering atmospheric pressure by touch. Instead, the instrument can be used purely visually; it provides a system that allows anyone, simply by visually reading off, to conclude that the weather will be fair or stormy. Someone unfamiliar with touch but well-versed at seeing could perfectly well be able to operate it. Barometers, Amo suggests, translate (or denote, retrace) properties accessible to one sense modality into another. Could a similar translation be available to the person in the situation that Molyneux sketches? The prospect here seems dim.

The sort of translation that would be required would be from properties accessible through the unfamiliar sense (vision), into the sense that the person is acquainted with (in this case, most likely touch).

First off, Amo thinks that touch is the most obscure of all senses. Recall that he deemed perceptibles of touch to have the “highest degree of obscurity”.That Amo thinks touch is most obscure does not by itself mean that perceptibles from other sense modalities could not be translated into ideas of touch. However, it does signal how Amo might not be too optimistic about this option. For touch’s obscurity does mean that if, hypothetically, such a translation were to happen, it would involve moving from a modality which (in Amo’s view) can capture a wide range of sensible qualities, to a modality which captures far fewer. Such translation would increase the degree of obscurity of the idea (because he has tied a sense modality’s degree of clarity or obscurity to the range of sensible properties that this sense is able to register, one might also capture this as involving the translation of ideas with higher complexity or information to ideas with lower complexity or less information). More importantly, Amo explicitly says that we cannot expect any relevant translation (or “denotation”) from ideas of other senses to that of touch:

In [the case of] the perceptibles of vision & audition we denote the thing by its proper qualities or parts; in [the case of] the remaining [perceptibles] we indicate one by another, or like by like; and analogous by analogous.We can denote perceptibles of olfaction by those of taste; [but] perceptibles of touch neither as such, nor by any other. (Amo 1738: 77)

I read his statement here not as contradicting his earlier points about barometers and thermometers. Rather, I see Amo as making the point that there is no system for denoting tactile properties. Without such a system or standard, there is nothing for perceptibles of sense modalities other than that of touch to be translated into.

Obviously, Amo is moving a bit fast here. He did not contemplate the possibility of haptic language, braille or other tactile denotation systems (many of which, to be fair, only came to fruition in the nineteenth century). However, here it matters not whether Amo is correct, or even charitable. Rather, it is how we may plausibly take him to have assessed the situation Molyneux presents, had he been confronted with the question. Amo claims that we cannot expect a translation (or denotation) from other senses into touch. That makes it extremely unlikely that he would envisage that a newly sighted person who gets sensory stimulation from the unfamiliar sense of vision would be able to translate those sensations “directly” into the familiar sense of touch,for which (we presume) they have geometrical shape ideas. Without such direct translation, this third option for potentially getting to a “Yes” answer to Molyneux too must be set aside.

Amo’s response to Molyneux’s question, and what it might tell us about Amo’s philosophy

Based on the current discussion, I conclude that had Molyneux’s question been put to him, Amo would likely have responded that a person newly sighted would not be able to distinguish visually between the geometric shapes of the two objects facing them; or, that any such distinction would be no better than a random guess. For, of the three main options considered here that this person may have to distinguish between the objects, there is good indication to think that Amo would hold none of the trio viable.

First, Amo would likely think that a person would not be able to see geometric shapes through their freshly acquired sense of vision directly. For Amo sees mathematical thought—of which geometric thinking is a part—as a habit. Habits are obtained through repeat exercise. Someone who is using a new sense for the first time is not at that point engaged in a repeat exercise. Hence they cannot be presumed already to have available to them a habit for having ideas of shape coming from that sense.

Neither does either of the two main alternative routes look viable. The option of drawing on general, non-modal (“exact”) ideas of shape, for example in the guise of geometric definitions, would have to be rejected. Because even though Amo sees definitional thinking as key to philosophising well, he still maintains that any actual cognitive act of thinking a definition (that is, thinking the definition of cube or of sphere) cannot but be bound to revive ideas from a particular sense modality. Someone unfamiliar with the sense of vision would then be bound to fall back on touch (or possibly audition) in thinking of cubes and spheres, however modality-neutral the formulation of their definition.

Equally, the suggestion also has to be set aside that the person tasked with making the distinction might be able to, in some way,“translate” directly from their unfamiliar visual sensations to the ideas of shape in a sense modality they are familiar with (most likely: touch). While Amo does think that, in principle, translation (or, as he sometimes calls it, “reduction” or “denotation”) from one sense to the other is possible, he deems touch a “most obscure” sense, and explicitly denounces the possibility of denoting anything into the sense of touch.

If Amo were to see no options for the person in question to exercise any habit of geometric thought—whether directly or indirectly—then it must be concluded that he would concur with the original proposer of the question, namely that the newly sighted person would “Not” be in the position to correctly distinguish between the two shapes using sight alone.

The “No” answer diagnosed here for Amo raises questions, namely: what, if anything, might it tell us about Amo’s wider ideas and philosophical orientation, if this indeed were his response? I suggest two points. Here’s one: if the inference offered here is correct, then it strengthens the indication that Amo is closer to Locke (and others who likewise answered in the negative) than is often recognised. Moreover, it places him at a further distance of intellectual affinity from authors who do reckon that someone who confronts two three-dimensional objects in an unfamiliar sense modality for the first time would be able to accurately tell them apart—including Leibniz.

In recent scholarship, it has not infrequently been proposed that Amo’s philosophy is close to that of Leibniz. In particular, authors have drawn comparisons between Amo’s thesis that the mind is impassive—it lacks sensation—and Leibniz’s claim that there is a “pre-established harmony” between substances. For example, Victor Emma-Adamah states that Amo “… side[s] more readily with the Leibnizian framework of pre-established harmony” (Emma-Adamah 2015: 156), while Justin E.H. Smith calls Amo’s view of the relation between mind and body “broadly Leibnizian” (Smith 2015: 23). There already was reason to proceed with caution here—Amo nowhere in his extant work discusses “harmony”, and he only mentions Leibniz as an example of someone who is “erudite”, not for his philosophy (Amo 1738: 21). The current counterfactual interpretation should make us even more wary of seeing Amo as a Leibnizian.

More important at this point is that Amo’s possible proximity to Locke is not often picked up on. Nonetheless it is quite relevant, as it can place in a different light not only Amo’s own philosophical orientation, but also that of philosophy in Germany in the 1730s. Amo himself does not mention Locke, but will have come to ideas from the author of the Essay through the work of Jean Leclerc, whom he cites throughout his Treatise.

Another factor may have been in the background, too. Apart from instigating Leibniz’s New Essays, Locke’s influence on German philosophy is often estimated to be of no great significance. As Klaus Fischer states: “It is true that around mid-century and beyond Locke attracted a certain following, but those who accepted his theories were minor figures and exercised very little influence on the future course of German philosophy” (Fischer 1975: 444). At the same time, as Andrew Brown has shown, there was some animus for Locke’s work, in particular at the university of Halle under the influence of Thomasius and colleagues. Halle saw the first publication of Locke’s collected writings (Leben und Schriften Johann Locke, in 1717) and a lecture course was organised on Locke’s Essay in the 1750s (that is, after Amo’s time) (Brown 1951: 477). As it happens, after defending his Impassivity dissertation at the University of Wittenberg in 1734, Amo was based at Halle for a few years. His Treatise, which of his two extant works shows clearest affinity with Lockean themes, was published there in 1738. It is not unlikely, then, that some of Amo’s later thinking on the topic of the mind and its ideas was affected by being based at what Brown calls “an early center for the diffusion of Locke’s ideas” (Brown 1951: 477).

This leads me to the second point. Amo artfully combines a Descartes-inspired insistence that the mind does not sense, but only operates spontaneously, with a commitment to the sense-based origin of all human ideas more commonly found in predecessors and contemporaries (such as Locke or Leclerc) who precisely did think sensation was a key capacity of the mind. If indeed certain themes in Amo’s philosophy are more pronounced in his later publications than in the earlier one, then that should give us pause. For even though Amo’s Impassivity embodies a striking, distinctive claim which clearly marks out his work in contrast with some others at the time, it will be important not exclusively to focus on that earlier, much shorter work, but rather to take Amo’s full oeuvre—insofar as it is available to us—into account when discussing his (hypothetical, plausible) philosophical responses.


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  1. A position also known, with reference to Aristotle (in whose work it technically does not appear) and Aristotelian traditions, as the “peripatetic dictum”. See Cranefield (1970) for discussion. ↩︎

  2. Amo’s proposal that ideas can be obtained with (contemplative) reflection again resonates with Locke’s claim that reflection can be a source of ideas—including of ideas of psychological categories such as willing and understanding, or of more abstract ones such as the idea of existence, unity, or power (Locke 1975: II.iii–vii ff). ↩︎

  3. Leibniz adds for clarification: “My view rests on the fact that in the case of the sphere there are no distinguished points on the surface of the sphere taken in itself, since everything there is uniform and without angles, whereas in the case of the cube there are eight points which are distinguished from all the others” (Leibniz 1996: II.ix.8). ↩︎

  4. Editions of Euclid’s Elements had been available in Europe since the fifteenth century, with the first Latin (1557) and German (1558) translations appearing the century thereafter. ↩︎