The sensorium: Animal, human and divine

The sensory, or sensorium, sometimes called the common-sense, was held to be a place in the brain to where the five external senses delivered their information. The soul, or mind, was held to be also there in the sensorium and was therefore able to perceive this information by virtue of being directly present to the incoming sensory data. Clearly, it would be absurd to suppose the soul needed its own eyes and ears to see and hear messages coming in from the external eyes and ears. Accordingly, it was assumed that the information simply had to be presented immediately to the soul, and somehow (though just how remained mysterious) the soul could perceive and comprehend the information. Newton summed it up perfectly well immediately before he first introduced God’s sensorium in Quaestio 20. In English in the 1717 Query 28, he put it this way:

This is not an idea that Newton invented to suit his own purposes. He was simply adapting a standard belief. It was generally accepted that the sense organs merely conveyed information to the soul, or the mind, and it was really the soul/mind that perceived what the senses were communicating to it (Henry and McGuire Reference Henry and McGuire2018, 589–91). We can see this, for example, in John Locke’s Essay Concerning Human Understanding:

So, although Newton talks of God seeing and thoroughly perceiving things, he is not thereby committed to the view that God has sense organs. For Newton, just as the soul can directly perceive things within the sensorium, so God can perceive things within his sensorium. And, since infinite space is “as it were… his sensory,” and everything is in infinite space, then everything is in God’s sensorium, or “immediately present” to his sensorium. Newton actually added to Query 31 in 1717 a comment that was not present in the Latin Optice:

God perceives things “by their immediate presence to himself” (ibid., 370).

Perception was clearly regarded as an important function of the soul, or mind, but it was not the only one. An equally important feature of the mind was the will. Perception and will were regarded at the time as the two main functions of the mind; once again, Locke’s Essay illustrates the point:

Newton evidently recognized these dual purposes and wanted to show that the analogy between animal, or human, sensories and the sensory of God could hold for both perception and willing. The first appearance of God’s sensorium, in Quaestio 20, discusses perception and comprehension, while the second, in Quaestio 23, focuses on God’s will. Although Newton himself does not use the word “mind,” preferring “sensitive Substance” (Substantia sentiens) in Quaestio 20, Samuel Clarke, in his exchange with Leibniz, suggests that for Newton the sensorium was “the place where the mind resides” (Clarke’s Third Reply, §10, in Alexander Reference Alexander1956, 33).

Now, Newton scholars have paid very little attention to these comments.Footnote ⁶ After all, they are brief, and seem to be mentioned in passing, with no build-up, and having mentioned them Newton quickly moves on to other topics. So, it has been easy for scholars to dismiss them as minor or even insignificant aspects of Newton’s thought. The only major study of these comments until very recently was itself focused on an aspect of these comments that seemed to confirm that Newton only meant them as nothing more than an intriguing metaphor. This was the article published in 1961 By Alexandre Koyré and I. B. Cohen, entitled “The Case of the Missing Tanquam” (Koyré and Cohen Reference Koyré and Bernard Cohen1961). Koyré and Cohen wanted to get to the bottom of the disagreement about the status of the sensorium between Newton’s great rival G. W. Leibniz, and Newton’s defender Samuel Clarke. In his famous exchange with Clarke, Leibniz wrote:

To which, Clarke replied:

Koyré and Cohen argued, on material grounds, that both might have been right. When Newton added the Quaestiones with these comments to the Latin Optice in 1706, he referred in Quaestio 20 to God “who in infinite space, his sensory, sees the things themselves…” Evidently Newton quickly realized he had made a theological error and revised this sentence simply by adding the Latin word “tanquam”, which can mean “as if,” or “so to speak,” or similar qualifications. So, the comment now read, as Clarke suggested, “who in infinite space, as it were his sensory…” (qui in Spatio infinito, tanquam Sensorio suo…) (Newton Reference Newton1706, 315; Newton [1717] Reference Newton1979, 370). Unfortunately for Newton, the relevant set of pages had already been printed by the time he sent the printers this correction, and so a new page had to be printed and stuck over the original in each set of pages. Clearly, it was an expensive and time-consuming mistake to put right.

Furthermore, Koyré and Cohen were able to establish that the printer had already sent out some copies of the book before Newton asked for the correction to be made. Always eager to read whatever Newton published, Leibniz bought one of the first copies to emerge from the printer, and so his copy was an uncorrected copy (at least this is what Koyré and Cohen surmise). If that was the case, then Leibniz was perfectly correct to say that he had read Newton saying space is the sensorium of God, “in express words.”Footnote ⁷

Newton’s determination to insert the “tanquam,” and Clarke’s insistence that Newton’s comment was “by way of similitude only,” seems to have been taken by scholars to indicate that Newton was not saying anything with any real significance. Accordingly, little more needed to be said about God’s sensorium.Footnote ⁸ In so far as it has appeared in scholarly discussion it is usually in connection with attempts to understand Newton’s views on the relationship between God and absolute space, and God’s sensorium is relegated to a merely incidental role (e.g. Koyré Reference Koyré1957, 235–72; Ray Reference Ray1991; Gorham Reference Gorham2011b).

Equally, however, Newton’s determination to immediately correct his first comment on God’s sensorium can be taken as an indication of its importance to him. It seems clear that, even after the addition of the tanquam to Quaestio 20, Newton still believed that infinite space and the world that occupied it were closely related in some way to the mind of God. As Patrick Connolly has recently shown, the most important aspect of Newton’s thinking about the sensorium was that he held it to be the place where an animal, or human, and by extension any thinking being, exercised their will. The sensorium of God, consequently, was the place where God exercised his will (Connolly Reference Connolly2014). The question remains, however, as to just why Newton introduced the sensorium of God into these two queries. Why did Newton need to invoke the will of God in just the way he did at these two separated points in the Queries?

The sensorium of God and theology

Although Newton immediately changed his initial suggestion that infinite space was God’s sensorium, to the weaker suggestion that it was merely similar to God’s sensorium; he made no changes to the second suggestion that God could move the bodies in the universe, that is in “his boundless uniform Sensorium” by an act of will. Bearing in mind that the correction to the first comment was costly and complicated, it seems that Newton must have had a serious reason for changing it. And yet, he saw no need to change the second comment about the sensorium of God. So, what was it that Newton felt was wrong about the first comment that it could not be allowed to pass into the hands of the reading public?

So far, the only attempt to provide an answer to this question has been provided by Patrick Connolly, author of the first study devoted to Newton’s speculations concerning God’s sensorium. Connolly has suggested that there was a theological problem with the first statement, but the second statement was perfectly compatible with sound theology as Newton understood it. Accordingly, the first had to be corrected, but the second did not (Connolly Reference Connolly2014, 194–96).

The problem, according to Connolly, is that the first statement presents God as a perceiver. Perceivers are passive, however, and can be changed by what they perceive (they might learn something, for example). In traditional theology, of whatever creed, God was always held to be supremely and purely active, and to consider him to be merely passive in any respect was to diminish his perpetually active agency in the world. Furthermore, God was always held to be completely immutable or unchangeable. Two considerations led to this assumption: firstly, God was held to be perfect, but changeability suggests a lack of perfection, a need to still seek perfection; secondly, there was no cause that could conceivably initiate change in the omnipotent and omniscient God.

Newton’s religion was unorthodox, but even he would never have deliberately denied the purely active nature of God, or that God was immutable. So, Newton recognized his mistake and took steps to correct it. He perhaps felt that the main thrust of what he was saying in the whole passage was clear enough, and theologically acceptable—namely, that the omnipresent God comprehends all things “wholly by their immediate presence to himself.” Now comprehending is an active enterprise, and to attribute comprehending to God is perfectly legitimate theologically. But Newton made the mistake of rhetorically building up to the comprehension of God—God sees all things, he perceives all things, he comprehends all things. Seeing was clearly meant metaphorically, perceiving was meant to imply a more thorough awareness of things than just seeing them, but should also be understood metaphorically, but what God really does, literally, is to fully comprehend all things, to fully understand them as the creator of them. So, although Newton perhaps felt that his main point, about God’s comprehension, was perfectly acceptable and could be taken literally, he realized that he needed to inform his readers that he only intended God’s seeing and perceiving metaphorically—hence the “tanquam”. Or so Connolly claims (ibid., 195).

It ought to be clear from this that Newton made no mistake when he wrote the second comment about the sensorium of God in Query 31. Here God is presented as supremely active, moving the bodies in infinite space by his will, and even forming and reforming the parts of the universe. Newton felt no need, therefore, to make any changes to this part of his text (ibid., 195–96). This is a good story, well told by Connolly, but in the end it remains unconvincing. The tanquam clearly qualifies the claim that infinite space is God’s sensorium. If Connolly were right it ought to qualify “sees the things themselves”—God, as it were, sees the things themselves.

There is a much simpler explanation for the single added tanquam. It seems reasonable to suppose that Newton did not want to commit himself to the view that infinite space was quite literally the sensorium of God, so that God’s sensorium was nothing more or less than infinite space. Similarly, he did not want to suggest that God had a sensorium in precisely the same way that animals and humans were said to have a sensorium (for example, he would not want his readers to assume that God’s sensorium was a place in God’s brain). In the General Scholium added to the second edition of the Principia (1713), Newton noted that “all discourse about God is derived through a certain similitude from things human, which while not perfect is nevertheless a similitude of some kind” (Newton [1687/1713] Reference Newton, Bernard Cohen and Whitman1999, 942–43). Presumably Newton felt that to understand God’s will, it helped to think of a sensorium from where it was enacted; but this only helped us to understand, and could not be said to be literally true. Accordingly, when he reconsidered Quaestio 20 he realized that he must add the tanquam (see also Kassler Reference Kassler2018, 112). Certainly, in several manuscript drafts of a 1716 letter to Conti Newton rejects a perfectly literal interpretation of these passages. For example, in one draft he writes of Leibniz that “He accuses me as if I said that God had a Sensorium in a litteral sense.” And in another he writes “as if any man except the Anthropomorphites ever feigned that God had a Sensorium in a litteral sence” (Koyré and Cohen Reference Koyré and Bernard Cohen1962, 109, 114).

There remains a problem with this account, however. If Newton’s concern was to avoid suggestions that God had a sensorium in a literal sense, then he should have also qualified the second mention of God’s sensorium. In this second mention he says that all the bodies of the universe are “within his boundless uniform Sensorium.” Surely, this calls for another tanquam? Unless Newton felt that, having made it clear thirty pages earlier that he was speaking merely of a similitude, he did not need to repeat the point (especially, because making a second correction to the already printed text would cause even more difficulty and expense). Accordingly, it seems fairly safe to assume that Newton felt he shouldn’t commit himself to a literal identification of infinite space with the sensorium of God, and so added the tanquam, the first time he wrote of it. He avoided the extra expense and inconvenience of correcting the second comment, simply by allowing the tanquam in Quaestio 20 to stand as a qualifier of both mentions of God’s sensorium. Certainly, if anyone objected to the comment in Quaestio 23, he could simply refer them back to the earlier comment, where he had already made it clear (he could legitimately claim) that he was speaking metaphorically. Newton had ample opportunities to adjust these comments for the 1717 edition, but he evidently did not feel the need to make any further changes.

Before moving on, it is perhaps worth noting that Leibniz did lay other charges against Newton’s talk of the sensorium of God. Evidently, Newton never accepted these as valid criticisms of his stance, and left it to Samuel Clarke in his famous published correspondence with Leibniz to defend his position. One of these charges was that if God was considered to have a sensorium then he must be a material being. Leibniz wrote to Clarke that “the word sensorium hath always signified the organ of sensation” (Leibniz’s Second Paper, § 3, in Alexander Reference Alexander1956, 16–17), and seems to have regarded it as a physical part of the brain. Clarke responded that “The word sensory does not properly signify the organ, but the place of sensation” (Clarke’s Second Reply, § 3, in Alexander Reference Alexander1956, 21). The implication seems to be that although sensation takes place in the head, it is not associated with a bodily organ. Clarke had already tried to impress upon Leibniz that Newton’s point depended upon the immaterial mind:

Instead of simply pointing to the tanquam and the metaphorical nature of Newton’s talk of God’s sensorium, Clarke tries to shift the focus from the sensorium itself to the immaterial mind, or soul, that is located there. This also serves to repel Leibniz’s objection that if God is said to have a sensorium, then he is said to have parts. God, as the supreme exemplar of what Descartes designated res cogitans, might be said to be all mind, and even if that mind is located, as it were in God’s sensorium, then that mind can still be one, simple, and indivisible (Connolly Reference Connolly2014, 192–94).

Certainly, Newton himself was quick to deny any suggestions that talk of the sensorium of God implies God has organs or parts:

In view of the fact that Newton, and Clarke, defended the suggestion that the world and all it contains existed “within his [God’s] boundless uniform Sensorium,” it seems clear that it was a suggestion that Newton felt captured something important about the nature of God, the world, and the relationship between them. The two mentions of the sensorium of God in the Queries, although very brief and seemingly included in almost a throw-away fashion, were evidently more important than might appear from a superficial reading. Although it is impossible to say to what extent Newton saw infinite space as somehow representing the sensorium of God, he seems to have felt that this “similitude” provided a valuable insight into the relationship between God and his Creation (see Kassler Reference Kassler2018, 104–25; and Henry and McGuire Reference Henry and McGuire2018).

The importance of this similitude is especially marked if we remember that Newton was by no means given to flights of fancy. In spite of his well known rejection of hypotheses in the General Scholium which he added to the second edition of the Principia in 1713, Newton did allow hypotheses if they seemed to him to be indicated and supported by empirical results. What he objected to in the General Scholium, and earlier, were hypotheses of the kind invoked by Descartes to explain gravity and the motions of the planets. “The hypothesis of vortices,” he wrote, “is beset with many difficulties” (Newton [1687/1713] Reference Newton, Bernard Cohen and Whitman1999, 939). Not only was there no direct evidence in its favor, but empirical evidence and mathematical analysis strongly suggested it was completely misconceived.

Elsewhere, however, Newton did offer his own hypotheses as tentative explanations for phenomena, but only when he could point to some empirical evidence in support of the putative explanation. Clearly, Newton felt that his hypothesis of the sensorium of God, and its concomitant account of God’s action in the world, were based on experiential evidence. As Newton wrote in Quaestio 20, “does it not appear from Phaenomena…”; and in Quaestio 23 he used the argument from design to insist that the “Contrivance” of the parts and instincts of animals “can be the effect of nothing else than the Wisdom and Skill of a powerful ever-living Agent,” and that furthermore, such an agent must be “more able by his Will to move the Bodies within his boundless uniform Sensorium… than we are by our Will to move the Parts of our own Bodies” (Newton [1717] Reference Newton1979, 370, 403).Footnote ⁹ In the second edition of the Principia, Newton made the more general point that “to treat of God from phenomena is certainly a part of experimental philosophy” (Newton [1687/1713] Reference Newton, Bernard Cohen and Whitman1999, 943; my emphasis).

As we shall see in the next section, the essential point of the idea that infinite space was comparable to something we might choose to call the sensorium of God, in so far as it is the place in which God exercises his will, was that God could create the world and everything in it merely by willing it into existence, just as we can move the parts of our bodies just by willing it. And if God could create the world, he could also move all of its bodies “within his boundless uniform Sensorium.”

The sensorium of God and the cause of gravity

To invoke the sensorium of God the way Newton does seems to be uniquely original. I know of no comparable discussion in the writings of any other natural philosopher, or natural theologian, much less in those of any religious author. We need to ask ourselves, therefore, what led Newton to this highly original way of thinking about God and his action in the world? Unfortunately, there seems to be no external evidence that we can bring to bear in helping us to answer this question. Newton does not discuss the concept of God’s sensorium in his correspondence, and if he discussed it with Samuel Clarke when he was defending Newton’s view in the correspondence with Leibniz, it must have been conducted orally by these two neighbors, and nothing was written down (Meli Reference Meli, Bertoloni, Iliffe and George2016, 590–92). Jamie Kassler has recently surveyed everything that Newton has to say about sensories—in animals and humans, as well as these two references to God’s sensory—but nothing in Newton’s discussions of animal and human sensories helps us to understand why Newton developed the idea of a corresponding sensorium of God (Kassler Reference Kassler2018).Footnote ¹⁰ Accordingly, we must proceed by a close reading of the two comments themselves, and their immediate context in the Queries.

So, let us begin by looking at the context when God’s sensorium was first introduced. I will refer to the English translations in the 1717 edition, and use the numbering of the relevant Queries in that edition (28 and 31—but in 1706 these were 20 and 23). Query 28 begins with a long, critical, and ultimately dismissive account of all attempts to explain physical phenomena by supposing the existence of an aether. It begins by rejecting aetherist accounts of light, but soon moves on to dismissing Descartes’s and others’ theories about the motion of planets through heavens filled with “fluid Mediums” (Newton [1717] Reference Newton1979, 362–68).

At this point Newton turns to what he considers to be the correct account of gravity and the motions of the planets:

Newton goes on to say that this correct view was dismissed by later philosophers, “feigning Hypotheses for explaining all things mechanically.” So, Newton has now led himself into a discussion of gravity and its cause. He knows that the cause of gravity is non-mechanical, because he established this in the Principia,Footnote ¹¹ but he does not have a ready answer as to what is the cause of gravity. So, at this point he brings God into the discussion:

At this point Newton introduces the argument from design to reinforce the existence of an intelligent first cause; “whence arises all that Order and beauty which we see in the World?” (ibid.) Among the various questions he lists which he believes can only be resolved by acknowledging a first cause is: “whence is it that the Sun and Planets gravitate towards one another, without dense Matter between them?” Still pursuing aspects of design in the world, he soon comes to animals:

This brings Newton to mention the will, and immediately after, the sensory of animals:

It is at this point that Newton makes the first of the two statements about the sensorium of God. Let us look at it again:

Now, there is a non sequitur here. Given the immediately preceding discussion, about the order and design in the heavens and in animals, we might expect Newton to say what appears from phenomena is that there is an all powerful designer God. That would, at least, have followed, but he does not really make that point at all. Instead he is seemingly side-tracked into saying that God, like animals and humans, has a sensory, and his sensory is somehow related to infinite space. Newton has brought infinite space into the discussion out of the blue.

What are we to make of this? It seems to me that we can only suppose that it made sense to Newton because he had already been dwelling on these matters for many years. It looks very much as though Newton is trying to give an abbreviated account of complex matters he has thought long and hard about, but has left out crucial connecting steps, and the result doesn’t really make sense to naïve readers.Footnote ¹² Perhaps Leibniz might have pointed out this non sequitur, if he had not been preoccupied by what he saw as the more dangerously materialist implications of Newton’s claims about the sensorium of God.

Be that as it may, we can trace out the salient points in the argument: Newton is concerned to explain gravity without introducing mechanical hypotheses; he thinks about God, the first cause, who is not mechanical; he then turns to the design argument as a way of reaffirming the existence of God, this leads him to wonder how animals and humans move their bodies merely by their will; and then he introduces the sensorium of God, which he likens to infinite space. Interestingly, and surely significantly, there is a very similar pattern of discussion in the second place where the sensorium of God is mentioned, as we shall now see.

Query 31 is the longest and richest of the Queries and starts off by reiterating Newton’s belief that all physical phenomena can be explained by assuming bodies are made of invisibly small particles which are endowed with attractive and repulsive forces “by which they act at a distance” (Newton Reference Newton1979, 375–76). What follows are various examples, chemical and physical, which Newton believes confirm his claim; “For we must learn from the Phaenomena of Nature”, he writes, “what Bodies attract one another, and what are the Laws and Properties of the Attraction…” (Ibid., 376).

Crucially, he brings this survey to an end by introducing Gravity into the Opticks for the second time:

Shortly after, God is brought in as the Creator of these particles and their properties, and after a short digression rejecting charges that he is resorting to occult qualities, Newton returns, for the first time since Query 28, to the argument from design to bring God once again into the proceedings.

As in Query 28, Newton quickly introduces animals into the discussion, and allows that to lead straight into his second claim about the sensorium of God:

It should be noted that there is no explicit mention of infinite space here. We can easily imagine contemporary readers asking themselves what are these Bodies within God’s sensorium? It is only if they remember Newton had already mentioned that infinite space is (as it were) God’s sensorium, that they might realize that Newton must be referring here to all the Bodies in the universe, which are now said to exist in God’s boundless sensorium. Presumably, therefore, infinite space in which all the bodies in the universe are normally held to exist, is God’s boundless sensorium, or is very much like it.

It can be seen, anyway, that in both places where the sensorium of God is mentioned, it follows on from a discussion of the cause of gravity. And in both places there is a clear sequence of discussion: the cause of gravity is introduced, Newton then uses the argument from design to affirm the existence of God, and then the sensorium of God is mentioned and linked to infinite space and the Universe. In order to make the transition from the design argument to God’s sensorium, on both occasions, Newton introduces the will of animals and humans into the account of divine design. In the second discussion of the sensorium of God, this leads Newton to refer to the mysteriousness of the way we can move our bodies by our will, and to the suggestion that God can move the bodies in the infinite space of the universe merely by exercising his will.

This repeated sequence is all the more striking, because each of the three elements in the sequence only ever appear in the Quaestiones, and later in the Queries, at these two points. The only two places in the Queries where the sensorium of God is mentioned, are also the only two places where the argument from design is invoked, and the only two places in the 1706 Optice, where the cause of gravity is discussed.Footnote ¹³ It seems clear, then, in spite of the somewhat obscure and elliptical way of introducing the sensorium of God into Quaestiones 20 and 23, and later Queries 28 and 31 (based merely on idiosyncratic correlation, rather than logical entailment), that Newton associated God’s sensorium with attempts to explain gravity. So, we need to consider just what Newton had in mind—how did talk of the sensorium of God help to explain gravity?

The cause of gravity was a real problem for Newton. Gravity, according to him, was an attractive force operating between bodies, and this attractive force was capable of operating across vast distances of empty space. For most of his contemporaries this was a completely unacceptable theory of gravity. The standard view, held by traditional scholastic philosophers and by those who subscribed to the new mechanical philosophy of Descartes alike, was that bodies could only act on one another by contact. For the mechanical philosophers, therefore, the reason why bodies fell to Earth was not because the Earth attracted them, but because there are streams of invisibly small particles perpetually descending towards the Earth which push anything above the Earth down towards its surface.Footnote ¹⁴ It was these mechanical philosophers Newton was referring to when he wrote that they had “banished” the correct cause of gravity, instead “feigning Hypotheses for explaining all things mechanically” (ibid., 369). Newton explicitly denied this mechanical explanation of gravity. There was, after all, no evidence in its favor. It was, as Newton pointed out in the General Scholium which he added to the second edition of the Principia (1713), merely an unsupported hypothesis and was not in any way “deduced from the phenomena.” These were the kind of hypotheses that “have no place in experimental philosophy,” and famously Newton refused to countenance them (Newton Reference Newton, Bernard Cohen and Whitman1999, 943).

For Newton, gravitational effects demonstrated that bodies were capable of acting upon one another without making contact (Henry Reference Henry, Schliesser and Smeenk2019; Henry Reference Henry2020).Footnote ¹⁵ Given that the force of gravity was clearly able to penetrate “as far as the centers of the sun and planets without any diminution of its power to act” (Newton [1687/1713] Reference Newton, Bernard Cohen and Whitman1999, 943), as he wrote in the General Scholium, it was presumably an immaterial force. It was a standard belief, unanimously accepted, that matter could not interpenetrate matter; two particles of matter could not occupy the same place at the same time. Accordingly, if the force of gravity could penetrate to the centre of material bodies, it must be an immaterial force. This only raises further problems, however. If the force of gravity could penetrate bodies without the process of penetration affecting the force in any way, how could the force move the bodies it was penetrating? Effectively, it was the same problem as the mind/body problem—how does the immortal soul, or the immaterial mind, cause the body to move? A body needs to be pushed or pulled to set it in motion, but how can something immaterial, which by definition simply passes through bodies, also provide bodies with impulsion or traction?

Although the operation of such immaterial forces remained unexplained, Newton and his followers believed that we have easy access to abundant evidence that immaterial substance can, one way or another, move bodies. We only have to raise our arms, or jiggle our toes.Footnote ¹⁶ As Newton himself had noted in his unpublished speculative piece, known by its incipit as “De gravitatione,” “each man is conscious that he can move his body at will, and believes further that all men enjoy the same power of similarly moving their bodies by thought alone…” (Newton [c.1672 or c.1684?] Reference Newton, Rupert Hall and Hall1962, 138).Footnote ¹⁷

We can put this together with a comment made later by John Locke in his Essay Concerning Human Understanding. In the chapter “On Power,” Locke wrote:

If we want to understand how motion is initiated, we should not consider bodies, but the working of our will. We can make our own bodies move just by an act of will.

One of the most remarkable features of “De gravitatione” is Newton’s attempt to explain the nature of body solely in terms of “extension and an act of the divine will” (Newton Reference Newton, Rupert Hall and Hall1962, 140). Newton suggests “that God, by the sole act of thinking and willing, can prevent a body from penetrating any space defined by certain limits” (ibid., 139). He goes on from there to show that such a region of impenetrable space might be made indistinguishable from body (reflecting light, sounding when struck, and so forth), and that indeed all bodies may be constituted in exactly this way.

It seems clear that Newton was very pleased with this speculation, and saw it not only as offering a new account of body, but also as extending the ways in which we are supposed to be made in God’s image (by showing the similarity between our will and God’s):

But Newton never published this, and he never returned to this concept of body in any later work. It does seem clear, however, that he adapted these ideas many years later, in order to offer a solution to the problem of the cause of gravity. If we can move the parts of our bodies by an act of will in our sensoriums, then God can move any and every body in infinite space, or, which is effectively the same thing, every body “within his boundless uniform Sensorium” (Newton Reference Newton1979, 403).Footnote ¹⁸ Newton’s speculation that infinite space might be somehow analogous to the sensorium of God, and that everything in the universe, therefore, might be said to be in God’s sensorium, enabled him to offer an explanation for what seemed to be gravitational attraction at a distance—it was God who brought about the movements we attribute to gravity. Newton might have repeated, slightly changed, the comment we have just seen him make in “De gravitatione”: “Thus I have deduced a description of gravity from our faculty of moving our bodies.”

We have independent evidence that Newton was indeed thinking along these lines. David Gregory, Savilian Professor of astronomy in Oxford, had privileged access to Newton and tells us of what they spoke about on December 21, 1705:

So, Gregory confirms here that when Newton was thinking about God’s omnipresence and his intimate presence to everything in the world, he was also thinking about the cause of gravity.

A draft of Query 23, written in English, also shows the link in Newton’s mind between the sensorium of God and gravity:

In the second mention of God’s sensorium in the published Optice, Newton was suggesting that just as we can move the parts of our own bodies by an act of will, so God can move the bodies in his “boundless uniform Sensorium”; that is to say, he can move the bodies in infinite space, merely by willing it. Accordingly, if a reader were to enquire about the cause of gravity, Newton had provided himself with a ready answer: the will of God is the cause of gravity.

Primary and secondary causes of gravity in the Queries

Newton did not leave it there, however. If he simply believed that God was the immediate cause of gravity then we would have to see Newton as a fellow-traveller with Continental Cartesian occasionalists, or at least as a thinker who allowed far more divine intervention in the world than was usual outside the ranks of the occasionalists. Indeed, evidence suggests that Newton’s position came close enough to the view that God was solely and immediately responsible for gravity that a number of his close associates believed that was his view. In the early 1690s, Newton’s friend and admirer, Nicolas Fatio de Duillier, and Christopher Wren both seemed to think that Newton believed gravity was caused directly by the will of God (Westfall Reference Westfall1980, 509–10). Similarly, we have seen that Gregory seemed to suggest in 1705 that Newton believed God to be the immediate cause of gravity.Footnote ²⁰

Certainly, Leibniz, writing in 1716, insisted that Newtonian gravity was “a supernatural thing” because it could not be “explained by the nature of things” (Leibniz’s Fourth Paper, §45, in Alexander Reference Alexander1956, 43), but only by supposing it is “God himself that performs it” (Leibniz’s Fifth Paper, §118, in Alexander Reference Alexander1956, 94). Furthermore, a number of modern commentators have followed suit and insisted that Newton believed in the direct intervention of God in the world, in order to bring about gravitational effects. R. S. Westfall suggested that “God was an incorporeal aether who could move bodies,” and that “every movement in the world was the immediate effect of His power” (Westfall Reference Westfall1971, 397, 398). Andrew Janiak has taken a similar line:

Similarly, for Geoffrey Gorham, Newton’s position was “very close to the occasionalist view” (Gorham Reference Gorham2011a, 24, see also 25, 32).

It might be supposed that I am now adding my voice to theirs by insisting that Newton believed gravity was caused simply and immediately by God’s will. However, it seems to me to be perfectly clear from the whole tenor of Newton’s writings, published and unpublished, that he was neither an occasionalist, nor close to being one. In spite of his suggestion in Quaestio 23 and Query 31 that God can move every body in the universe simply by an act of his will, it is evident that he did not regard God as the only cause operating in the universe. Moreover, he certainly does not continually refer his readers to the will of God to explain phenomena—neither in this query, nor elsewhere in his writings. On the contrary, he continually refers his readers to the regularly operating secondary causes in nature through which the primary cause, God, has chosen to operate. “The main Business of natural Philosophy,” he wrote in Query 28, “is to argue from Phaenomena… and to deduce Causes from Effects, till we come to the very first Cause” (Newton [1717] Reference Newton1979, 369). We arrive at the first cause, God, at the end of a process of deduction based on earlier secondary causes, derived from our observation of phenomena. This is abundantly clear just from the Queries, where God is only invoked in the discussions leading up to the two mentions of his sensorium; otherwise Newton explains phenomena throughout by reference to natural causes—usually attractive and repulsive forces operating from the particles of bodies (e.g. Newton [1717] Reference Newton1979, 339, 371, 372, 373, 375–76, 383, 384, 385, 386, 389, 391, 392, 393–94, 395). Similarly, although Newton writes in the General Scholium (added to the second edition of the Principia in 1713) that the world is contained in God, “In him all things are contained and move,” he immediately goes on to say that “he does not act on them” (Newton [1687/1713] Reference Newton, Bernard Cohen and Whitman1999, 941). This is obscure, but it seems to mean that God does not act directly on “all things”, preferring to let them act in their own right (in accordance with the laws of nature he has instituted) as secondary causes. It is shortly after this that he reminds us that he has “explained the phenomena of the heavens and of our sea by the force of gravity;” and declares “that gravity really exists and acts according to the laws that we have set forth” (ibid., 943). In taking this line—that the primary cause, God, chose to operate through natural secondary causes—Newton was simply accepting the standard view, embraced by natural philosophers and theologians alike (except for the occasionalists).

It can be seen just how far from being an occasionalist Newton was by comparing him with his close friend Samuel Clarke. Clarke has recently been convincingly revealed to be a “partial occasionalist” who believed that gravitational effects could only be brought about by the direct intervention of God, or by angels delegated by him (Sangiacomo Reference Sangiacomo2018). In order to convince his readers that the direct intervention of God is required to make an apple fall to the ground, or to keep Saturn in its orbit, Clarke has to first demonstrate (at least to his own satisfaction) that material bodies are categorically passive and inert, and that not even God can endow bodies with active powers, such as the power of attraction. It is the nature of bodies to be inert, Clarke insists, and not even God can change that (Henry Reference Henry2020).Footnote ²² Accordingly, Clarke argues, what looks like gravitational attraction has to be brought about by God, or angels, moving the relevant bodies in the appropriate ways (in accordance with the law of gravity). There is nothing like this in Newton’s writings. Nowhere does Newton claim that bodies cannot be endowed with powers, much less that God cannot bestow such powers. On the contrary, Newton routinely refers to the powers of bodies, including their attractive and repulsive powers (Heimann and McGuire Reference Heimann and McGuire1971; Downing Reference Downing, Biener and Schliesser2014; Henry Reference Henry2020). Moreover, Newton was a voluntarist in his theology and consequently did not believe that God’s creative power was restricted by foreordained essences or natures of things. While Clarke insisted that the nature of bodies was such that not even divine omnipotence could make bodies active, for Newton, if God wished to superadd activity to passive matter, he just could (Henry and McGuire Reference Henry and McGuire2018; Henry Reference Henry2020).

Accordingly, we can discern what is effectively another explanation for gravity in Quaestio 23 and Query 31—that is to say, an explanation for gravity that does not refer to the direct intervention of God. Right at the outset of this Query Newton reminds his readers that “it’s well known, that Bodies act upon one another by the Attractions of Gravity, Magnetism, and Electricity” (Newton [1717] Reference Newton1979, 376). Having shown throughout this longest of the queries how the “small Particles of Bodies” attract one another and thereby explain chemical phenomena, Newton finally comes to gravity:

After a digression in which he dismisses the Cartesian claim that the “quantity of Motion in the World” is always the same, Newton returns to gravity:

The cause of Gravity is now said to be one of several active Principles at work in the world. It is at this point, somewhat abruptly, that God is brought in to the exposition:

These “other Properties” include the aforementioned active principles:

Newton is by no means clear in his exposition at this point. Having first of all suggested that there is an active principle which is “the cause of Gravity,” he now tells us that gravity is an active principle. Perhaps his meaning is simply that gravity is a principle of activity placed in matter by God, and therefore, it can be said that the cause of gravity simply is the active principle. In the same way that heat might be said to be an active principle placed in fire, and so we can refer to the active principle as the cause of heat in fire. Or perhaps Newton is simply writing loosely or hastily. After all, he continues the quotation above:

So, what he really meant to say was, “such as that which causes gravity, and that which causes Fermentation, and that which causes Cohesion.” It seems safest to assume, therefore, that Newton saw active principles as the causes of phenomena such as gravity, fermentation, cohesion, magnetism, electricity, and the other “attractive Powers” that he mentions in the course of this query. In this regard, they are similar to the active principle which is said to enable us to move our own bodies: “Thinking is an active principle by which we move our bodies according to our will”, Newton wrote (Newton c. 1704–1718, Cambridge University Library MS Add. 3970.3, f. 620v). So, gravity is an attractive power which moves bodies, and is caused by an active principle in bodies.

Almost immediately, however, he complicates the issue again by saying that he considers these active principles to be laws of nature:

This is very problematic, and seems irresolvable. At first, an active principle is said to be the cause of gravity, and this principle is a law of nature; but then we are told that things are formed by the laws of nature, even though the causes of these things are not yet known (ibid.). Newton seems to say that laws of nature (active principles) are the cause of things, and then to suggest that there are unknown causes operating in a regular way, which enable us to formulate laws.

Newton is clearly unaware of his confusion—or, at least, unaware that he is writing in a way that readers can only find confusing. Although necessarily speculative and ultimately undecidable, I believe it is possible, by close reading, to understand how Newton went astray here.

If we start at the beginning of the paragraph, Newton tells us that particles of matter have a Vis inertiae, a force of inertia, and this ensures that the particles follow certain laws of nature (laws which are entailed by the existence of inertia): “Particles have… a Vis inertiae, accompanied with such passive Laws of Motion as naturally result from that Force” (ibid.). Clearly, Newton is referring here to the three laws of motion which appear at the beginning of the Principia (all of which are indeed based on the principle of inertia) (ibid., 416–17). So, inertia determines how bodies move (as summed up in the three “passive” laws of motion), but, he goes on, their movements are also determined “by certain active Principles, such as is that of Gravity…” It should follow, therefore, that just as inertia leads us to laws of motion, so should the active principles. Passive inertia leads to passive laws, active principles lead us to active laws—such as the law of gravity. Presumably Newton believed that there must also be laws of fermentation, of cohesion, of magnetism and of electricity, and of the probably existing “more attractive Powers than these,” but these laws have not yet been discovered (Newton [1717] Reference Newton1979, 376).

Now, one reason we know the law of gravity is correct is because the truth of it appears to us from the way it coincides with our daily experience of gravitational effects. This is what Newton means when he writes that things themselves are formed by the laws, “their [the laws’] Truth appearing to us by Phaenomena” (ibid., 401). So, at this point everything seems clear. Newton believes that empirical phenomena lead us to the conclusion that there is an active principle which is the cause of gravity. This active principle acts in such a regular and predictable way that we can arrive, indeed we have arrived (thanks to Newton), at a law of gravity. The validity of the law then establishes that the starting premise—that gravity is caused by an active principle—is correct.

Things go wrong, I believe, because Newton is tempted at this point to digress into a response to charges that he has reintroduced occult qualities into natural philosophy. The digression has all the hallmarks of something developed separately from this discussion of the cause of gravity. Perhaps Newton had already decided that the way to dismiss this charge was to distinguish, as he does here, between “manifest Effects” and occult causes. Gravity, magnetism, and electricity have very visible and striking effects, and we can learn a great deal from those effects, even if we do not know how they are caused. This was a perfectly standard way of defending the use of unexplained effects within Baconian experimental philosophy (Henry Reference Henry1986), and Newton is simply adopting it here.

We can see this for example, in Robert Boyle’s New Experiments Physico-Mechanical Touching the Spring of the Air and Its Effects (1660). Undecided as to the cause of the elasticity of air, Boyle declares that it is not his intention “to assign the adequate cause of the Spring of the Air, but onely to manifest, That the Air has a Spring, and to relate some of its effects” (Boyle Reference Boyle, Hunter and Edward2000, 1:167). Similarly, in his Of the Systematicall or Cosmicall Qualities of Things (1671), Boyle wrote:

Similarly, Robert Hooke insisted that “unheard of Powers, Operations, Effects or Motions” could be introduced into natural philosophy providing an experimenter can “daily try, see, and find the regular working of them,” thereby bringing them “within our reach and command” (Hooke [1678] Reference Hooke1931, 179).

So, we can see this digression in Query 31 as Newton taking the opportunity to respond to accusations from Leibniz and other Continental mechanical philosophers that he was merely resorting to occult qualities in his discussion of gravity, by making what must have seemed to him (working in the heartland of Baconianism) a very obvious, and very effective response, namely, that he was dealing experimentally with manifest effects, which revealed the detailed operations of whatever caused those effects, even if those causes remained occult, or hidden (Newton [1717] Reference Newton1979, 401).

Unfortunately, however, it was a feature of this standard Baconian response to accept that causes remained occult. Newton followed suit, and ended up implying that he did not yet have a casual account of gravity. So, Newton begins the paragraph by telling his readers that gravity is caused by an active principle placed in matter by God, but then allows himself to be diverted into dismissing charges that he resorts to occult qualities, and ends the paragraph by saying that he leaves the cause of gravity “to be found out” (ibid., 402).

Newton perhaps saw himself as introducing this standard Baconian defense of the use of occult or unexplained causes (legitimate if the effects of these causes can be demonstrated empirically) to Continental, and largely Cartesian, readers. This was prepared, after all, for the Latin edition of his work on optics. Newton used the same Baconian argument a few years later in the General Scholium added at the end of the second edition of the Principia (1713). On this occasion, however, there was no contradiction. In the Principia Newton did not allow himself to speculate, and so he was perfectly correct to say, “I have not yet been able to deduce from phenomena the reason for these properties of gravity” (Newton [1687/1713] Reference Newton, Bernard Cohen and Whitman1999, 943). Our concern here, however, is with the speculative causes for gravity that Newton had already provided at the end of the Optice, and later repeated in the 1717 Opticks, where he was “proposing only some Queries…” (Newton [1717] Reference Newton1979, 339).

The Queries were added to the end of the Opticks as a way of rounding off what was essentially an unfinished work, and they provided Newton with the opportunity to put forward various speculations that he suspected were correct, but which he could not establish with any certainty. The material presented in the Queries, therefore, differs greatly from that presented in the Principia. Newton was heavily criticized for failing to provide a causal account of gravity in the first edition in 1687, and by the early 1690s (according to Fatio, Wren, and Gregory) he was evidently already thinking about the role of God in any putative explanation of gravity. Gregory tells us that he was thinking about these matters again in 1705, and in the Optice of 1706 he made public, in Quaestio 23, his belief that God could form and reform parts of the universe just by thinking about it. As we have seen, these speculations about God were closely linked to attempts to explain gravity, but gravity was not declared to be enacted solely and immediately by God because, as Newton wrote, “it may be also allow’d that God is able to create Particles of Matter … of different Densities and Forces” (ibid., 403–04). Gravity was said to be caused by active principles which God imposed on these Particles (ibid., 401).

By the time Newton was ready to publish the second edition of the Principia, in 1713, the musings about the cause of gravity in Quaestio 23 remained entirely speculative. Consequently, when Newton decided to discuss the nature of gravity in the General Scholium, which he added at the end of the revised Principia, rather than introduce his speculative account of gravity, he chose to meet Continental critics of his theory head-on. Their alleged casual accounts of gravity were entirely speculative and not deduced from phenomena, he forcefully pointed out, while his account, though lacking a supposed cause, was entirely derived from phenomena and “sufficient to explain all the motions of the heavenly bodies and of our sea” (Newton [1687/1713] Reference Newton, Bernard Cohen and Whitman1999, 943).Footnote ²⁴

Even so, when he issued the second English edition of the Opticks, Newton showed no reluctance to return to his earlier speculations. He added eight new Queries and made changes to some of the earlier ones (Hall Reference Hall1993, 127–62), but he left his comments about the sensorium of God and the associated account of gravity unchanged. It seems clear from this that he felt that these particular speculations continued to point to something important about the nature of the world, and of God’s relationship with it.

One thing seems abundantly clear from Newton’s introduction of the sensorium of God into the Optice, and from the opinions of Fatio, Wren, and Gregory, as recorded in Gregory’s memoranda (Westfall Reference Westfall1980, 509–11; Hiscock 1937, 29–30), and that is that Newton felt a greater need to discuss the role of the primary cause than was usual in natural philosophy. Although all were agreed that God was the primary cause who established and maintained the smooth running of the secondary causes, it was usual to simply take God’s role for granted, and to focus discussion on the workings of the secondary sources. This had been the standard approach among natural philosophers since the Middle Ages (Grant Reference Grant2007, 239–73). It was clearly important to Newton, however, that natural philosophy should help us to understand God as well as nature: as we have already noted, he wrote in the General Scholium that “to treat of God from phenomena is certainly a part of natural philosophy” (Newton [1687/1713] Reference Newton, Bernard Cohen and Whitman1999, 943).Footnote ²⁵

This may simply have been an aspect of Newton’s undeniably intense religious devotion. But, it may also have been a result of what Newton saw as the inherent difficulty of explaining to his contemporaries (especially as many of the leaders among them were mechanical philosophers) an attractive force that operated at a distance. The Principia demonstrated that gravitational attraction acted at a distance, across space that was devoid of intervening matter. The force of gravity had to be immaterial, therefore, and yet still be capable of moving matter. Newton must have known that this theory of gravity would attract dismissive criticism, or, if he did not know, he soon became aware of such criticism, from Huygens, Leibniz, and others. In order to persist in assuming that an immaterial force could move matter, Newton (presumably after long thought, throughout the 1690s and up to Reference Newton1706) drew attention to the fact that our immaterial souls can move our bodies, though we do not know how we do it. If we can do that, then surely the omnipotent God can move all bodies, even though he is completely immaterial. The discussions of God’s sensorium in the Quaestiones are intended to bring this out. But, in case anyone should think that God must therefore be acting directly in the world he immediately cautions:

Newton could have chosen to say that God simply brings about gravitational effects by his own direct intervention in the world, after all, French occasionalists had already taken this previously unprecedented line in natural philosophy. Newton did not sign up as an occasionalist, however, choosing instead to suggest that it appears “from Phaenomena” that God’s will decrees that bodies attract one another by an immaterial force. Even though we do not know how that is possible, it is not significantly different, Newton implied, from our ability to move our own bodies (without us knowing how that is possible). Furthermore, it is evident from the law-like way gravity behaves that it must have been established by God. Accordingly, God established active principles in the particles of matter which he created, and those principles cause an immaterial power of attraction.