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1.3 A problem and a solution: Kant's metaphysical principle of succession

In this section, I discuss a problem with Kant's early conception of change. In section 1.2.5, I argued that Kant defended the anti-Leibnizian doctrine that every change, or at least every change of a body's motion, involves the exercise of a transeunt force. The problem lies precisely in the manner in which I qualified this claim in the preceding sentence: Kant may have defended physical influx for bodies only, not for substances generally. Since Leibniz might plausibly be interpreted as having defended pre-established harmony for monads and physical influx for bodies, Kant's own discussion of influx may not have been as anti-Leibnizian as I have made it out to be [44].

I discuss two solutions to this problem, one speculative and one based on an idea Kant published in the 1750s. The speculative solution is what I call the "indifference thesis:" Kant may have spoken indifferently about bodies and substances because he believed that the points he raised about bodies also applied to other types of substances [45]. If this thesis can be attributed to Kant, then his defense of influx should be interpreted as applying to all substances, including simple substances as well as bodies.

I discuss these points in section 1.3.1. In section 1.3.2, I discuss how Kant's metaphysical principle of succession, which he defended in the New Elucidation of 1755, provided a decisive solution. In the context of this principle, I argue, it is clear that Kant intended his defense of physical influx to be general and not restricted to bodies only. While there is no evidence that Kant had formulated the principle of succession in its final form when he published Living Forces, I conclude that there is evidence that Kant had developed the principle in 1747, or at least that he had accepted something akin to it.
 

1.3.1 Physical influx for bodies, pre-established harmony for monads?

I have shown that the first three sections of Living Forces contained the rudiments of arguments for physical influx and against pre-established harmony. It is important to emphasize that, although this result was anti-Leibnizian, it was not a criticism of the vis motrix view, since that view was compatible with physical influx and, indeed, many of its defenders did not defend pre-established harmony [46]. What I have shown is that Kant's arguments against the vis motrix view illuminate Kant's own rejection of pre-established harmony. I raise this issue because it is extremely important to my study of Kant's solution to the mind/body problem. As I show in section 1.6 below, Kant's rejection of pre-established harmony was essential to his views on space, interaction, and his claims about the sense in which souls exist in space and interact with other substances.

For now it will suffice to note that one conclusion Kant drew was that change always involves the exertion of an externally-directed force. Whereas Leibniz had held that force is always internally-directed, Kant maintained that a substance's own force, considered in isolation from the effects of other substances, can never be a ground for its own changes. Examining briefly how Kant used this idea in later pre-critical texts will help us better to understand its somewhat prolix employment in Living Forces to solve the mind/body problem.

In the New Elucidation of 1755, Kant defended the principle of succession, which stated "no change can happen to substances except in so far as they are connected with other substances; their reciprocal dependency on each other determines their reciprocal changes of state" (1:410). This principle remedied what Kant may have seen as an important limitation in his argument in the first sections of Living Forces, which discusses bodies only. As I discuss in section 1.4.1 below, there is some evidence that Kant spoke indifferently of bodies and other substances in Living Forces—that is, that he believed that the points he made about bodies applied equally well to other types of substances. The evidence about this is far from clear, however, and unless this point can be substantiated, Kant's discussion of pre-established harmony in Living Forces appears vulnerable to the charge that it applied to bodies only and not to monads.

Since in this period Kant held that bodies were ontologically derivative substances composed of monads, a defense of physical influx among bodies would not go far enough [47]. Unless the indifference thesis could be substantiated, Kant's original argument did not exclude the possibility that pre-established harmony might hold true for monads. In this case, however, could not defenders of pre-established harmony assert that their theory explains the true source of change [48]?


1.3.2 Kant's answer

Although it is difficult to say with confidence whether Kant believed that the argument of Living Forces applied to substances generally, his discussion of the principle of succession eight years later was admirably clear. This principle asserted that no substance undergoes change unless it is acted on by another substance [49]. Thus the principle of succession applied to substances in general the same lessons that Kant drew about bodies in the first sections of Living Forces: no substance has the power to change itself, and all change in a substance involves the action of another substance. Although he did not defend them explicitly, these conclusions are important to Kant's argument in Living Forces. As I show in section 1.6, Kant argued that immaterial substances like souls can change only if they are in real interaction with the community of bodies. If Kant's arguments against pre-established harmony applied to bodies only, then he would have no basis for concluding that the community of genuine interaction includes souls as well as bodies [50].

 

1.4 The "general concept of active force" and the real possibility of temporal order (Living Forces, part I, §4)

In Living Forces section four, Kant tried to show that a transeunt force that causes change in substances' internal states could be the cause of both motion in bodies and representations in souls. As I explained earlier, Kant thought that the vis motrix view was incompatible with mind/body interaction [51]. Because they believed that force only causes changes in motion, Wolff and others defended a conception of bodies' force that was incompatible with change in souls' perceptual states, a change that does not seem to involve only motion. In Living Forces section four, Kant articulated his own conception of a broader conception of change that was compatible with mind/body interaction.

Specifically, Kant discussed change in a substance's internal determinations that is caused by an externally-directed force. As I explain in section 1.4.1, I call this change transeunt internal change. I am specifically concerned in that section with explaining why Kant thought that transeunt internal change could be the cause of bodies' motion. In section 1.4.2, I compare and contrast Kant's understanding of internal change with Leibniz's. This provides the background necessary for a detailed analysis of the argument of section four, a task which occupies sections 1.4.3, 1.4.4, 1.4.5., and 1.4.6. The last three of these sections are chiefly concerned with Kant's important doctrine that in our world force is exerted gradually, bit by bit over time. I call this doctrine the "nach und nach thesis."

I conclude by arguing that although Kant's understanding was weakened by the dogmatism that prevails throughout Living Forces, he nonetheless articulated a vision of change that supported a greater range of activity than did either Leibniz or the defenders of the vis motrix view. In sections 1.5 and 1.6, I show how Kant parlayed this new account of change and action into a solution to the mind/body problem.


1.4.1 Change is not just change in motion: Kant's account of transeunt internal change

In Living Forces section four, Kant discussed the notion of transeunt internal change. Leibniz believed that the only effect of a substance's force was a change in that substance's own internal states. Kant's conception of change was broader than this in two respects: he believed that transeunt or externally-directed force was involved in every change and he believed that force could have external effects including changes of motion. Kant's view was also unlike the vis motrix view, which held that force may be transeunt but is always external because forces cause changes in motion only.

As I show in sections 1.5 and 1.6 below, Kant believed that only his conception of transeunt internal change provided the resources for solving the mind/body problem. In this section, I focus on another facet of Kant's discussion of active force in Living Forces section four, namely the manner in which his doctrine that in our world active force is exercised in our world as a transeunt or externally-directed force provided him with an explanation of bodies' motion [52].

In section 1.2, I explained Kant's criticisms of Leibniz's successors, who identified the force of bodies with vis motrix. However, I have not yet answered a basic question: If the effect of force is not always a change of motion, exactly what else can the effect be? Unfortunately, Kant's answer was unsatisfyingly abstract. Leibniz's followers, he argued, went astray by giving a specific definition of force as whatever changes a body's state of rest or motion. Kant posited a broader and more abstract explanation of the effects of force: substance A exerts a force on substance B just in case A's agency changes the inner states or determinations of B. Kant outlined this view in Living Forces section four, where he argued specifically that this change provided the sufficient reason for bodies' motions and changes of motion. As I explain in section 1.6 below, this point was crucial for Kant's project of showing that a single force could cause both motion in bodies and representations in souls.

Here is how Kant explained his understanding of transeunt internal change and its relation to the motion of bodies:

At the beginning of this passage, Kant adopted what looks like a Leibnizian position: force is measured by its effect, and the effects of force are changes in the "internal states" of substances. Leibniz understood the internal states of monads to be perceptions, and he argued that monadic change occurs when a monad's essential force changes its own perceptions. Unfortunately, Kant did not explain what he took the internal states of substances to be. If they are perceptions, then his view would have differed from Leibniz's by affirming genuine interaction: a monad's perceptions change because it is acted upon by the internal force of other monads.

Leibniz argued that God's harmonization of the monads entails that each substance's internal "script" is coordinated so that each monad "mirrors" the states of all the rest of the monads. Nothing of the sort went on in Kant's understanding of internal change, for Kant rejected pre-established harmony and adopted a conception of transeunt force. I stated above that Kant's account of transeunt internal change was unsatisfyingly abstract. One reason for this was that Living Forces provided no textual evidence explaining what Kant meant by internal change. Kant spoke only of abstract "determinations," and avoided saying more by reminding his audience that a completely abstract definition of change avoided the pitfalls experienced by Wolff and other supporters who appealed to vis motrix as the basis of a specific definition of change [53].


1.4.2 Four principles of monadic change

This problem was partially mitigated by Kant's use of several Leibnizian principles of monadic change. It is useful to list these here, even though I won't discuss the textual evidence for them attributing them to Kant until later in this chapter and in Chapter Two. The principles are:

I show in section 1.6 below that the notion of internal change (or change in a substance's inner states) was central to Kant's solution to the mind/body problem: Kant believed that if one does not think of change in terms of internal change, then the mind/body problem is insoluble. If all change involved changes in external relations, Kant assumed, change would only involve changes of motion. As I have emphasized throughout this chapter, a central thesis of Living Forces was that there are other types of change in addition to change in motion.

It important also to emphasize the extent to which Kant's conception of internal change was not Leibnizian. In contrast to Leibniz, Kant maintained that the spatiotemporal world constituted a genuine unity and he believed that that bodies and monads are united by the same principle of change. Finally, and as I have already explained, Kant's principle of change, in contrast to Leibniz's, appealed to transeunt force.


1.4.3 The argument of §4

Although he did not define it precisely, Kant's notion of transeunt internal change supported a comprehensive metaphysical explanation of the world. In Living Forces section four, Kant specified the relation between abstract inner change and the motion of bodies. Here is my reconstruction of his line of argument:

My reconstruction captures three striking features of Kant's argument. The first two features relate to Kant's own philosophical beliefs. The first is that, as the steps one and two demonstrate, Kant used a specific account of active force, namely an account of a transeunt or externally-directed external force. As I have already mentioned, this made Kant's view staunchly anti-Leibnizian, for Leibniz denied the existence of transeunt forces. The second feature concerns Kant's argumentative strategy, which, as step eleven shows, accorded the principle of sufficient reason a central role. This represents an important parallel between the argument of section four and Kant's argument for the principle of succession in the New Elucidation [54]. In each case, Kant applied the principle of sufficient reason to argue that there must exist a sufficient reason why a substance exerts its force on particular substances at different moments.

The third feature captured by my reconstruction concerns a potential problem with Kant's argument: Kant began with claims about substances in general, but he ended by referring to bodies in relative motion in space. Although Kant was committed to the existence of several types of substances, for example material bodies and immaterial souls, his argument appears to have taken little heed of these distinctions. As I suggested in section 1.3.1 above, the most charitable response to this problem is to hold that Kant was merely indifferent to them because he believed that his claims apply equally well to all kinds of substance [55]. This may be true, but it is a major thesis of this dissertation that Kant's early dualism was unsatisfactory because Kant could not prove that souls did not have the same material mature as the simple constituents of bodies. A less charitable but equally-plausible interpretation of Kant's apparent sloppiness to keep straight claims about different types of substances is that Kant lacked the conceptual resources necessary for drawing all the ontological distinctions that he wanted to draw [56].

I discuss this problem in Chapter Two. As I explain in detail in section 2.4, despite his clear intention to distinguish between material and immaterial substance, it became difficult for him to avoid the problematic, untenable view that monads and souls are all material in nature. I introduce this difficulty now because it proved so important for the development of the critical philosophy: as I argue in Chapters Three and Four, Kant's recognition of this problem, and his responses to it, prompted him to ask questions that led him to several important critical insights.

The focus of this chapter remains understanding exactly what Kant asserted about mind/body interaction in Living Forces. To do this, it is essential to understand what Kant asserted in section four about the relationship between change, motion, and temporal succession. As I argue in section 1.6, Kant's reflections on these topics led him directly to his first solution to the mind/body problem.


1.4.4 The "nach und nach" thesis: time and the deferment of vis activa

Kant thought that his account of a transeunt force that caused inner change could also explain the motion of bodies. As he put it at the start of section four, "There is, however, nothing easier than to derive the source of that which we call movement from the general concept of active force" (§4; 1:19). Namely, as steps three and four summarize, Kant conceived of transeunt internal change as the source of motion. Motion exists because substances exert force on each other "nach und nach" (§4; 1:19), which in this context means gradually, a little bit at a time. If this were not the case, Kant stated, there would exist no motion [57].

By the "nach und nach thesis" I mean the claim that our world is one where force is exercised gradually, a little bit at a time. Kant apparently found it obvious that a world where substances expended their force immediately would contain no motion, for he stated this dogmatically. As Kant put it at the end of the first paragraph of section four, if the world were like this, then the exercise of vis activa could be explained without our having to "name the force of bodies" or appeal to the concept of motion (§4; 1:19). Thus Kant believed that, to explain motion, we must assume that the nach und nach thesis is true or that substances in our world exercise their forces gradually over time [58].

This idea provided Kant with a novel explanation of the source of motion: motion is the effect of a transeunt internal force that is exercised gradually over time, which is to say that motion is caused by the deferment of the exertion of force. If the monadic substances that constitute our world were not able to resist each other's vis activa, the nach und nach thesis would not obtain and our world would be motionless. Kant thus held that our world is composed of substances that have both an active and a passive power: every substance exerts force on other substances, and each substance resists the force impressed on it by other substances. According to Kant, therefore, the defenders of the vis motrix view were right to think that motion is grounded on substances' force, but they erred in thinking that the exercise of force cannot cause anything else besides motion [59].


1.4.5 A speculative defense of the nach und nach thesis

I have said that Kant assumed that the nach und nach thesis obtains because his aim was to explain the source of motion. In this section, I speculate about whether Kant had any other reasons for thinking that the nach und nach thesis obtains. I concentrate on two ideas, namely (1) that a body must act with all its force and (2) that the thing it acts upon is capable of being acted on just so much and no more. The first idea came from Kant's presupposition that a force is measured through its effects: it makes no sense to attribute to a substance a force that never has an effect. The second point was an assumption that Kant made about bodies: they can suffer or endure only so much change.

As I have explained it so far, the argument of section four shows only that, a substance cannot exert all of its force all at once on one other substance if that substance is to be thought of as the ground of motion. Could not such a substance exert all its force at one moment, namely by exerting some portion of it on a number of different substances? If the universe only contained two substances, then from this Kant would be entitled to conclude that, if substance A cannot exert all its force at once, then it must exert its force at some later time. However, consider the case of a world with three substances such that substances B and C could each endure exactly one-half of substance A's force. In this case, could not A could exert all its force at the first moment, namely by acting simultaneously on B and C? Since we possess clear criteria for distinguishing one substance from another (namely, their internal states), there seems no conceptual problem with the notion of a substance acting at the same time on two or more separate substances. However, in this case B could not endure any force exerted by C and, likewise, C could not endure any force exerted by B. It would follow that B and C would have to exert their force on substance A, and that they would be able to exert their force at the first moment only if substance A could endure the entire quantity of each of their forces. This would happen, for example, if substances B and C possessed relatively little vis activa or if substance A was able to endure relatively great amounts of this force.

It is hard to know what Kant would have described this seemingly empirical claim about the ratio of the quantity of force to the ability to suffer change. Unfortunately, he said almost nothing about the crucial notion of a substance's inability to endure unlimited quantities of vis activa. Perhaps Kant assumed that each substance would "repulse" enough vis activa to require successive exertion of force. This would be guaranteed if the ratio of total quantity of force there is to be exerted to force endured were high enough: for example, substances would necessarily exert their force over time if it were the case that a substance that could endure one unit of vis activa at a single moment had two units to expend. Although Kant could not prove this directly, he surely considered the existence of movement in our world sufficient reason for concluding that our world must be such that substances express their force over time.

However, even this was far from what Kant required. He asserted that, after the initial moment where A acted on B, at the next moment A goes on to exert its force on another substance, substance C. This is strange, because could not substance A exert its force on B bit by bit over time? At the very least it seems plausible to suppose that B might be able to endure more of A's force at a later time. Although Kant did not discuss this possibility, he might have argued like this:

To say that substance B has endured as much vis activa as it is capable of enduring seems to entail that some time must pass before it can endure any more force. If at the very next moment B could endure more force, then it simply seems wrong to say that at the first moment B could have endured no more. If Kant were to assume that B could recover the ability to endure more force only at some later moment, then step 6' would give him what he needed: If there is no time when substance A is not active, then at the very next moment, when substance B is incapable of enduring more force, A must exert its remaining force on some substance other than B.


1.4.6 From the nach und nach thesis to motion—and a host of problems

This argument would have provided Kant with an explanation of the real possibility of the existence of motion in our world: the ground of the real possibility of motion is the fact that the nach und nach thesis obtains in our world. Unfortunately, Kant did not provide many details about how this argument was supposed to go.

Thus far I have shown why Kant may have believed that substance A could not expend all its force on substance B and why, at the very next moment, it would move on to exert its force on substance C. It is important to recognize that this "movement" occurs at the metaphysical level and is analogous to motion but is not literally motion: all Kant has shown is that, after acting on B, A subsequently acts on C [61]. Kant asserted dogmatically that substance A would possess a different "relation of location and position" with respect to substance B and with respect to substance C (§4; 1:19). Kant used step eleven to move from this to conclusions about motion:

Kant asserted that the only possible ground is that A is in motion relative to B and C or, as he put it, "A changes its place in that it acts successively" (§4; 1:19). There are several reasons why Kant's claim is hard to understand. Kant's provided little detailed argument, and, on the face of it, the leap from successive action to motion is a non-sequitur of considerable grossness.

Consider Kant's perplexing argument that A cannot bear exactly the same spatial relationships to substances B and to C.

At the first moment of exertion of force, A bore a certain relationship of position and location to B. Although Kant gave no specific examples of the relations he had in mind, he asserted that they provide a ground or sufficient reason why A acted on B at that moment. If C bore exactly the same relations to A, then "there would be no ground for A's not having acted initially on substance C as it did on B" (§4; 1:19). Applied to bodies, this argument seems perfectly reasonable. As I show in Chapter Two, Kant believed that bodies possessed two primary forces, a force of attraction and a force of repulsion, the intensity of each of which varied according to distance. Suppose that, at a certain time, a body A exerted an attractive force on two other bodies, B and C. Since the intensity of the attractive force varies with distance, if B and C were the same distance from A, then A would exert the same degree of attractive force on both bodies. Indeed, if distance determines the intensity of force, then the only reason why A could exert different degrees of attractive force on B and C would be that B and C were not the same distance from A. Suppose further that body A initially exerted five units of attractive force on body B and one unit of force on body C, and that at a subsequent time A exerted one unit of force on B and five units of force on C. This would imply that A was in motion relative to B and C: A would have moved away from B and toward C.

The argument of section four was organized around two distinct claims. According to the nach und nach thesis, the real possibilities of space and spatial relation are grounded on our world being one where substance A is unable to exert all its force on substance B. Later in the argument, Kant spoke of body A, and he made claims about motion that make sense only if force follows the model of the attractive and repulsive forces of bodies. Unfortunately, these two claims appear to be inconsistent: on the physical force model of universal attraction, all things continually act on each other and it is never the case that one thing can no longer endure another's force.

Kant provided a few hints for unraveling these confusions. In the next two sections, I examine two important arguments that Kant made about the relationship between substances' vis activa and bodies' physical force. The first, which maintained that all substances are in space, is an application of Kant's conclusions about motion in section four. The second drew upon the first as well as on the nach und nach thesis. This argument contained Kant's proposed solution to the mind/body problem [62].

I address these points in sections 1.5 and 1.6. First, however, I close section 1.4 with some general reflections on the argument of Living Forces section four. Earlier I argued that Kant's argument for physical influx had two main weaknesses: Kant had no response to occasionalism and his discussion of pre-established harmony may not have excluded the possibility that physical influx is true of bodies but not of monads. Kant's project of explaining real possibility was also incomplete, for he never attempted to explain the real possibility of interaction. Since his accounts of change, force, motion, and time all presupposed interaction, this omission limited the philosophical depth that Kant could reach in Living Forces. Fortunately, Kant addressed many of these problems in subsequent works. For example, just as the metaphysical principle of succession bolstered Kant's defense of physical influx (see above section 1.3.2), the principle of coexistence was meant to demonstrate the real possibility of interaction [63]. In Chapter Two, I examine the fruit that Kant's first work bore in the 1750s.

Living Forces was a dogmatic text based on incomplete philosophical project. Nonetheless, Kant's first publication was an important work, both because it set forth large elements of Kant's pre-critical metaphysical system and because—as I show in Chapters Two, Three, and Four—here for the first time Kant raised issues and problems that set him on the path towards the critical philosophy. Under no illusions that Kant's first work was complete or tenable on its own, in the remainder of this chapter I will sketch out as clearly as possible the remainder of Kant's metaphysical vision, with the goal of making understandable its most important element, Kant's first solution to the mind/body problem.

 

1.5 First application of Kant's account of vis activa: All substances in our world are in space (Living Forces, part I, §§7-8)

In this section, I connect Kant's notion of transeunt inner change with his explanation of the unity of our world. It followed from the argument of Living Forces section four, I maintain, that our world is unified spatially. From the specific manner in which the nach und nach thesis is realized in our world, two important conclusions followed. The first conclusion was that all of the substances in our world are located in space. The second was that each substance possesses an attractive force that attracts all other substances in accordance with Newton's inverse square law of universal gravitation. As I discuss in greater depth in Chapter Two, Kant conceived of gravity as the omnipresent force that unifies our world [64]. Here I focus on the first claim, that every substance in our world exists in space. This section is divided into three sub-sections. In sections 1.5.1 and 1.52, I discuss Kant's general metaphysical understanding of worlds. Section 1.5.2 also addresses Kant's specific account of the unity of our world, an account that I use in section 1.5.3 to show how the argument of Living Forces section four can be extended to show that all the substances in our world have a spatial location.


1.5.1 Kant's definition of a world

In Living Forces sections seven and eight, Kant affirmed the possibility of a plurality of actual worlds. He defined a world as a whole that is not a part of anything else. A world is not itself a substance, but rather is a composite of the substances that constitute its parts. These parts compose a genuine unity in virtue of the way that they relate to each other. Specifically, a world is unified in virtue of the principle of influx that specifies the manner that substances can act on each other. As many actual worlds are possible as are principles of influx; Kant concluded "it is actually possible that God has created many millions of worlds" (§8; 1:22). Each world would consist of a set of substances that are connected together by a different type of influx. Kant sometimes called this type or principle of influx the form or schema of a world [65].


1.5.2 The varieties of worlds

Kant conceived of two broad categories or types of worlds, each of which contained a different type of substance. First, a world may contain just one substance, namely a solitary substances that is capable of interacting with nothing else. This is the limiting case: a solitary world has a form that makes impossible any influx. Second, there are worlds that contain several finite substances, all of which interact with each other in virtue of a principle of influx. In these populous worlds the nach und nach doctrine either holds true, in which case the world contains motion, or it does not, in which case the world is static and, Kant suggested, is not a spatial world [66]. That our world contains motion implies that it is a world of the second type whose form or schema involves a principle of influx that causes vis activa to be expended successively.

Worlds, for Kant, denoted limits of interaction: no substance in one world can interact with a substance in another world. Solitary substances are, by the nature of the schema of their worlds, incapable of interacting with anything else. Nor can substances in two populous worlds interact: if two worlds' principles of influx permitted inter-world action, then the worlds would each be parts of a greater unity, not wholes that are parts of nothing else. It follows that each of the spatiotemporal worlds is unified by a schema that allows its substances to interact with each other but not with the substances in any other world.

Kant maintained that each populous world where the nach und nach thesis obtains would have a different type of spatiality. The schema of our world, he believed, is such that in it the nach und nach thesis is realized in a way that causes the substances in it to interact in a three dimensional space where Newton's inverse square law of universal attraction holds true. It is just because our world is one where substances act outside themselves in a certain way that our world has these features. Our world is not unified with the substances in other worlds precisely because those substances possess different forces and exist in a different type of space. In those other worlds, the specific nature of substances' exertion of vis activa makes possible different types of interaction and spatiality [67].


1.5.3 The argument of §4 extended

Recall the argument of section four:

Kant's discussion of worlds in sections seven and eight of Living Forces allowed him to conclude that in worlds where the nach und nach thesis obtains, all substances—material and immaterial—are located in space:

Step thirteen followed from Kant's definition of a world. Kant took himself to have shown in section four that, in each world where the nach und nach thesis obtains, the world's schema or form is such that its substances interact via an influx that puts them in spatial relation to each other. To show that all the substances in our world are located in space, Kant required two things: (1) knowledge that our world is one where the nach und nach thesis obtains, and (2) an argument that the nach und nach thesis entails that substances bear spatial relations to each other. The first point Kant considered inductively proven by everyday experience [68]. The second Kant considered himself to have demonstrated in section four. Kant concluded that the ground or sufficient reason why substance A exerts its force on substances B and C at different moments is that that A bears different relations of position and location to those substances. Since the nach und nach thesis requires interaction to be successive, this conclusion guarantees that nach und nach worlds are spatial, i.e. are worlds composed of substances that bear spatial relations to one another. Thus all the substances in our world are located in space.

The crucial point for the purposes of this work is that Kant applied this conclusion to all the substances in our world, material and immaterial alike. In particular, souls, which he considered immaterial substances, are located in space. This proved crucial to Kant's proposed solution to the mind/body problem.

 

1.6 Second application of Kant's account of vis activa: Kant's first solution to the mind/body problem (Living Forces, part 1, §§5-6)

In this section, I present and evaluate Kant's first solution to the mind/body problem. In section 1.6.1, I argue that Kant understood the traditional mind/body problem to presuppose several false interrelated assumptions, namely that bodies' force is vis motrix, that bodies act only by causing changes of motion, that bodies can be acted upon only by being moved, and that souls and bodies do not share a common force. In sections 1.6.2 and 1.6.3, I discuss why Kant believed that the vis motrix view was incompatible with mind/body interaction; these sub-sections address, respectively, the difficulties with matter acting on mind and the difficulties with mind acting on matter.

In section 1.6.4, I discuss Kant's own solution to the mind/body problem. I argue that his account of mind/body interaction can be understood as an application of his account of transeunt inner change. In accordance with the divine schema of our world, both souls and bodies possess a vis activa that is exerted successively (see section 1.4 above), and that has as its effect both the production of motion in bodies and the production of representations in souls. This follows because a condition of being in our world is being located in space, and a substance can be in space only if it is capable of acting on and being acted upon by every other substance in the world.

On Kant's account, a soul is capable of causing a body to move by changing the inner states of the monadic substances of which the body is composed and a body is capable of causing representations in a soul by changing its inner states. In section 1.6.5, I criticize Kant's argument for being dogmatic, for failing to exclude the possibility of an objectionable hylozoism, and for presupposing a metaphysical dualism that is extremely difficult to understand. This last problem is the chief topic of Chapters Three and Four. To summarize one argument I make in Chapter Two, if, as I argued in section 1.5 above, Kant's understanding of the divine schema of our world entails that each substance in our world continually exerts an attractive force on every other substance, then there is reason to worry that souls are the same type of simple substances as the monadic constituents of bodies. Although this conclusion would seemingly strengthen Kant's claim that souls and bodies are capable of interaction, I argue in Chapters Two and Three that it contradicts one of Kant's specific doctrines about mind/body interaction and that the view amounted to an odd and possibly objectionable form of materialism, according to which souls are not matter but are of a material nature [69].


1.6.1 Kant's understanding of the mind/body problem in 1747

Kant conceived of the mind/body problem as a series of related difficulties with understanding how souls can act on bodies and how bodies can act on souls. In each case, Kant argued, the difficulties arise only if one assumes that vis activa is vis motrix. He titled Living Forces sections five and six "the difficulties regarding the action of body and soul which arise from the view that body has no other force than vis motrix" (§5; 1:19-20) and "the difficulty which similarly arises regarding the action of soul upon body, and how through the introduction of vis activa it can be removed" (§6; 1:20). The first paragraph of section six demonstrates how Kant approached the mind/body problem:

Kant maintained that the alleged difficulties with mind/body interaction all share several false assumptions: that bodies possess vis motrix only, that a body can act only by causing motions in itself or something else, that a body can be acted upon only by being moved, and that the moving force of bodies is alien to whatever type of force immaterial substances possess. These assumptions generated two main difficulties for understanding mind/body interaction. First, if a body can act only by exerting vis motrix, then a body can act on a soul only if it can cause the soul to move. But, Kant objected, such an explanation would do nothing to explain the characteristic effect of matter on the soul, namely the production of representations. If bodily force is a moving force, he concluded, the body's power to produce mental representations is an unfathomable mystery. The second problem is closely related to the first. If bodies can be acted upon only by being caused to move, then the assumption that the essential force of the soul is not vis motrix (but some unknown power) provided no basis for explaining how souls could act on bodies. For these reasons, he concluded, the vis motrix view entails that the nature and possibility of the mind's action on the body are hermetic puzzles that philosophy will never crack.

Kant believed that the traditional conception of the mind/body problem was wrong on all counts. He believed, first, that both main assumptions were false and, second, that applying his account of vis activa could dissolve all of the alleged problems with the action of the mind on the body and the action of the body on the mind. In a slogan, Kant believed that the crucial question was not whether bodies and souls can move each other, but rather was whether each can affect transeunt internal change on the other [70].
 


1.6.2 The difficulties with matter acting on mind

If the vis motrix view were true, Kant admitted, it is indeed mysterious how "matter can be capable…of generating representations in the soul of man" (§5; 1:20). Here is how he put the problem:

If the vis motrix view was correct, then motion would be the only effect that matter could cause. Kant found it is "paradoxical" to think that something that can cause motions only could "impress certain representations and images on the soul" (6; 1:21). To think that motion could do this, Kant judged, was an inconceivable non sequitur.

Of course, Kant himself denied that motion is the only effect of the exertion of a body's force. As I have shown in sections 1.2 through 1.4 above, he believed that the primary or essential effect of force was change in a substance's inner states. To be sure, he also maintained that motion may be a secondary effect of the exertion of vis activa; this is the case in those worlds—including our own—whose schema or form determines that vis activa is exerted successively. However, even in worlds where the nach und nach thesis holds true, Kant's position was that matter can exert force without causing any motion, which was what his prized but obscure example of a sphere resting on a table was meant to demonstrate [72].

 

1.6.3 The difficulties with mind acting on matter

Kant held a similar attitude about the alleged mystery of the mind's action on the body. If the vis motrix view is correct, then the action of the mind on matter is just as mysterious as the action of matter on mind. On the vis motrix view, the mind could act on matter only if it could cause the body to move, but once again this seems impossible because immaterial substances are "things of so entirely different an order from motions" (§5; 1:20).

However, as I have already shown, Kant denied that matter can only be acted upon by being moved. According to his monadism, matter is composed of monadic or simple substances. Matter changes, Kant concluded, when and only when a monad's internal states are changed by another monad's vis activa. As he argued in Living Forces section four, the motion that we sometimes observe accompanying change is a secondary phenomena that arises when vis activa is exerted gradually over time. Kant believed that the mind/body problem is dissolved "when the force of matter is viewed not in terms of motion but in terms of those effects in other substances that we are not in a position to define more precisely" (§6; 1:21). Indeed, it was precisely by attempting to define Leibniz's notion of vis activa more precisely that Leibniz's successors generated the difficulties with understanding force, action, change, and mind/body interaction [73]. Kant's own notion of transeunt inner change was designed to turn away from the vis motrix view and recapture the philosophical utility of a vis activa whose activity is understood—in a general sense only—to cause change in a substance's inner states. [74]
 

1.6.4 Kant's solution

I have explained Kant's strategy for solving the mind/body problem, but have not yet evaluated the details of his solution. Uppermost among the questions about Kant's solution are whether his account of vis activa and transeunt inner change could really account for the body's capacity to cause representations in the mind and explain the real possibility of matter being acted on by an immaterial substance. Kant's line of reasoning continued the extended argument of the opening sections of Living Forces:

Kant argued that the real possibility of interaction between our bodies and our souls is guaranteed by the way that, in accordance with the divine schema, the nach und nach thesis holds true in our world. Kant's argument rests on two claims. Against the vis motrix view, Kant argued, it is possible for bodies to act without causing motion, and it is possible for bodies to be acted upon without being caused to move. Kant's example of a sphere sitting on a table provided him with a concrete model of this: the sphere acts on the table in a way that involves no motion, for the weight of the sphere presses down on the table even when the sphere is at rest. Kant's deep point about change was that this case is no different from those where change is accompanied by motion: at the most fundamental level, all change is change in a monadic substance's inner state. When the internal states of the monadic constituents of a body change in this manner, the body often moves, although, as the sphere example was meant to demonstrate, this is not always the case. Thus there is no mystery about how an immaterial soul could cause a body to change motion: like all the other cases of action in our world, a soul acts on a body by exerting its vis activa in a manner that causes transeunt inner change in the bodies' constituent monads.

The possibility of a body acting on a soul can of course be explained in exactly the same manner: a body acts on a soul by exerting vis activa on the soul in a manner that causes the souls to undergo transeunt inner change. Kant's solution gave him what he thought he needed to explain specifically why it is possible for bodies to act on souls in a way that causes changes in souls' representations. Unfortunately, his argument dogmatically presupposed that "the whole inner state of a soul" is nothing but a manifold of representation (§6; 1:21). Although rationalist metaphysicians had long held similar views, Kant did nothing to defend or explain this claim. He could perhaps be excused for not defending a philosophical commonplace of his time, but in this case his silence vexes contemporary interpreters.
 

1.6.5 More problems: hylozoism, dogmatism, an unproven dualism

One problem is understanding how Kant distinguished the monads out of which bodies are composed from the monads that are identical with souls. Was his view that the inner states of the former—what he later called "physical monads"—consisted of manifolds of representations? If so, Kant would be hard pressed to avoid the hylozoism he criticized in Leibniz [76]. However, if the inner states of certain monads were not manifolds of representation, would not this require him to justify his claim that the inner state of each soul is simply "the compound of all its representations" (§6; 1:21)? By design, Kant's conception of monadic inner change was bereft of specificity – he described this change as causing "effects in other substances that we are not in a position to define more precisely" (§6; 1:21). Unfortunately, Kant's account of monads themselves was similarly imprecise, an imprecision that would eventually prove fatal to the system of metaphysics he developed in the 1740s, 1750s, and early 1760s [77].

Just as Kant's defense of physical influx was marred by his failure to refute ocasionalism, so too his monadism required defense against hylozoism. As I show in the next chapter, the problems multiplied after Kant attempted to address these problems. I argue in Chapter Two that the principles of Kant's physical monadology left him with no resources for proving that souls are not physical monads. As my reconstruction of Kant's argument in Living Forces shows, however, Kant was firmly committed to metaphysical dualism, and he remained so throughout the 1750s and 1760s. By the late 1770s, avoiding this problem caused Kant to abandon his assumption that souls are substances—and with this most of the rest of his earliest system of metaphysics. The lessons Kant learned proved important indeed: in Chapter Four, I show how, in the mid-1770s, important elements of the critical philosophy began to emerge from the wreckage of Kant's ambitious metaphysical vision of Living Forces.

 

NOTES

44.  Kant left open the possibility that changes of a body's motion always or sometimes have two causes, namely another body's externally-directed vis activa and the original body's internally-directed vis activa. There is no evidence in Living Forces that Kant believed this, but he did not rule out this possibility. In the Metaphysik Herder (1762-64), however, Kant was reported as teaching that one thing's being acted on by another presupposes both "outer" and "inner" grounds (28:82). This might be evidence that Kant thought every change involved both externally- and internally-directed vis activa, but unfortunately this intriguing notion falls outside the focus of this study. For a partial translation of the Metaphysik Herder see Karl Ameriks and Steve Naragon, editors and translators, Immanuel Kant: Lectures on Metaphysics (Cambridge: Cambridge University Press, 1997).

45.  I owe this point to Hannah Ginsborg.

46.  I am grateful to Daniel Warren for pointing out this possibility.

47. On this see Eric Watkins' unpublished manuscript, "From Pre-established Harmony to Physical Influx: Leibniz's Reception in Eighteenth Century Germany." I am grateful to Eric for providing me with a copy of this manuscript.

48. Unfortunately, pursuing the extremely general question of the status of bodies in Kant's early ontology would take me too far afield from my discussion of Kant's solution to the mind/body problem. There is a large question about exactly what Kant inherited from Leibniz's account of the dependence of the phenomenal on the non-phenomenal. One interesting question is this: Since we have a concrete idea of force that relates to spatiotemporal changes in bodies, what content is there to a metaphysically abstract notion of force that makes no reference to bodies, space, or time? I suspect that, in the pre-critical period, Kant may not have had the resources to answer this question satisfactorily.

49.  Leibniz and Wolff both entertained the idea of asserting pre-established harmony among monads while also asserting interaction between bodies. What makes this position coherent is the ontologically derivative status of bodies in their systems—in Leibniz's case as merely "well founded phenomena". For a discussion of their positions see Richard Miller, "Leibniz on the Interaction of Bodies," History of Philosophy Quarterly 5 (1988), 245-255 and Charles Corr, "Christian Wolff and Leibniz," The Journal of the History of Ideas 36 (1975), 241-262.

50.  It would be interesting (though a topic for a different study) to trace the exact relationship between these arguments and their critical counterpart, the Second Analogy of the Critique of Pure Reason. The Third Analogy bore interesting relations to Kant's principle of coexistence, which I discuss in Chapter Two.

51.  Unfortunately, this response proved to be not much of an argument against pre-established harmony. As I show when I discuss Kant's arguments for the principle of succession in section 2.3 below, Kant was fairly dogmatic and his position may have amounted to ruling pre-established harmony out without argument.

52. See section 1.2 above.

53.  It is unfortunate that section four was not included in the most readily available partial translation of Living Forces into English, Kemp Smith's partial translation in John Handyside's Kant's Inaugural Dissertation and Early Writings in Space (Westport, Connecticut: Hyperion Press, 1929).

54.  See section 1.2.3 above.

55.  I discuss this argument in detail in section 2.3.1 below.

56.  This line is plausible only if one understood what Kant might have meant by referring to the internal states of bodies. I believe that he had the resources to make this clear: following Leibniz, he could have maintained that bodies have distinctly internal states in virtue of the internal spatial relations and motions of their parts. I am grateful to Daniel Warren, who pointed out this possibility to me.

57. Another reason—related to this one—concerns a problem with Kant's early ontology: Kant did not specify in what sense or how the monadic realm grounds the realm of bodies.

58.  In assigning space a phenomenal status, Kant was of course following Leibniz. However, Kant's explanation of this status differed markedly from Leibniz's. A point that I owe to discussion with Hannah Ginsborg and Daniel Warren is that for Leibniz, space had a merely imaginary status; space and motion were imaginary manifestations of physical relations of well-founded phenomena. Kant followed Leibniz in thinking that the unity of space and time depends on the unity of the monadic realm, but in contrast to Leibniz he believed that space and time have a genuine unity. Although the details of his position were complex, Kant believed that Leibniz's ultimate ground for assigning space this status was his doctrine that substances do not act on one another. On Kant's own account, space and time have a phenomenal status, but this status depends on the fact that substances do interact. Although I cannot pursue this topic in depth in this study, I explain one source of this important difference between Kant and Leibniz when I discuss Kant's notion of composite unity in section 2.1 below. To maintain the focus of this study, I must acknowledge these interesting questions and move on.

59.  I owe this characterization of Kant's presupposition that the nach und nach thesis holds true in our world to Daniel Warren.

60.  Kant's pre-critical distinction between exerting and suffering vis viva was a model for his critical distinction between receptivity and spontaneity. This connection is made clear in the lectures on metaphysics. In the Metaphysik Mrongovius (1782-3), substances are portrayed as simultaneously active (in that they can exert their "power" in a way that changes the inner determinations or the outer relations of other substances) and passive (in that they it suffer the power of other substances): "The possibility of acting is a faculty, and of suffering receptivity….Every substance is self-active, otherwise it could not be substance; it can be suffering in one relation, but can also be active…" (29:823). As in Living Forces, Kant held that all substances exist in an interactive community characterized by the "transeunt action" of externally-directed force (29:823). Similar statements are found throughout the lectures; for example, according to the Metaphysik Dohna (1792-3), he stated that "real connection is reciprocal influence (acting and suffering)" and "a multitude of substances without real connection makes no world" (28:657).

Of course, Kant's critical understanding of what it means for a substance to exert, suffer, or resist power differed considerably from his account in Living Forces. Most notably, the notion of vis activa dropped out of his discussion of substances' power. Instead, he appealed to the results of "natural science," which provide one with "good reason to regard the attractive and repelling powers as primitive powers" (29:821) and he adopted a skeptical attitude towards cognition of substances' inner states. What Kant retained was a model of the action of substances in an interactive community that appealed to substances' externally-directed forces, the exertion and suffering of which determined their inner determinations and outer relations. A work from late in the pre-critical period, the Metaphysik Herder (1762-64), stressed that "if two substances effect one another reciprocally" then one substance suffers change "not merely by its own but rather also by external power" (28:52).

61.  Kant wrote: "Substance A…works always continuously into other substances" (§4; 1:19; emphasis added).

62.  At least one astute reader of Living Forces failed to draw this distinction. Of the very few critics who mention Living Forces, most pass over section four. An exception is Susan Meld Shell, who devotes the second chapter of The Embodiment of Reason: Kant on Spirit, Generation, and Community (Chicago: Chicago University Press, 1996) to Living Forces. Unfortunately, Shell's brief analysis of section four conflates the metaphorical "moving on" from B to C with A's literal motion.

63.  The second argument occurs first in the text. However, because Kant's solution to the mind/body problem presupposes that all souls are in space, it is convenient to comment on it after examining Kant's argument that all substances are in space.

64.  I thus disagree strongly with Paul Guyer's and Allan Wood's interpretation of the principle of coexistence as a dogmatic "retention of Leibnizian theory." This view is mistaken on two counts: First, Kant used the principle of coexistence to strengthen his anti-Leibnizian argument. Second, Kant used it not dogmatically, but rather to counter dogmatic assumptions that real interaction is possible. For Guyer's and Wood's views see their introduction to their translation of the Critique of Pure Reason (Cambridge: Cambridge University Press, 1988), pp. 27-28.

65.  See section 2.3 below.

66.  I discuss Kant's notion of the divine schema of a world at length in Chapter Two.

67.  Although Kant's views of the dependence of spatiality on the nach und nach thesis are extremely difficult and interesting, a detailed examination of them falls outside the scope of this study.

68.  Kant developed these points later in Living Forces. Although he admitted that "the ground of the threefold dimension of space [in our world] is still unknown" (§9; 1:23), he concluded that "it is probable that the threefold dimension of space is due to the law according to which the forces in substances act upon one another" (§10; 1:24). Namely, Kant believed that the likely explanation for the space of our world being three dimensional is that in our world the nach und nach thesis is realized in a way that entails the inverse square law of gravitation: "the threefold dimension seems to arise from the fact that substances in the existing world so act upon one another that the strength of the action holds inversely as the square of the distances" (§10; 1:24). The implausibility of Kant's sketchy speculations is not important here. What matters is the general principle upon which those speculations were based, namely that God could create worlds with different types of interaction and, consequently, different types of spatiality. Here is Kant's clearest statement of this position:

69. Kant's discussion contained an interesting anticipation of his critical doctrine that space and time are forms of intuition. In Living Forces he argued that there is a special fit between our specific mental constitution, our knowledge of the world, and our world's divine schema. In Living Forces section twelve, Kant wrote:

 Whether or not Kant is entitled to claim this I have already discussed above; see section 1.4.4 above.

70.  See section 2.4 below.

71.  Kant's approach was different in the critical period, and yet his solution was in some respects similar. In 1787, in the Conclusion to the Solution of the Psychological Paralogism of the second edition of the Critique of Pure Reason, Kant gave this characterization of the mind/body problem:

Although he cast the problem in terms of the critical discussion of inner and outer sense, Kant's solution hearkened back to his pre-critical position: it is possible, he argued, that mind and body are appearances of the same substance and hence that mind/body interaction is no more difficult to explain than body/body interaction. In the second edition of the Critique of Pure Reason Kant argued that the mind/body problem can be solved if one understands "how a community of substances is possible at all" (B428).

72.  In his notes to the Metaphysik Herder (1762-64), Gerhard Lehmann refers to Berkeley's objection to matter generating mental representations. One of Berkeley's last works, Siris: A Change of Philosophical Reflexion and Inquiries Concerning the Virtues of Tar-water (1744), was translated and published in Germany in 1745. Berkeley concluded that "..all phenomena are, to speak truly, appearances in the soul or mind; and it hath never been explained, nor can it be explained, how external bodies, figures, and motions should produce an appearance in the mind" (Lehmann's notes to 28:42). Lehmann's note is cited in Karl Ameriks' edition of the Lectures on Metaphysics (Cambridge, Cambridge University Press, 1997), p. 553.

73.  See section 1.4.4 above.

74.  See section 1.2 above.

75.  See section 1.4 above.

76.  Kant speaks of the Zusammenfassung of representations (§6; 1:21).

77.  Among other places (including the well-known passage in the Amphiboly of the Concepts of Reflection section of the Critique of Pure Reason, A266/B322), Kant criticized Leibniz on this ground in the Foreword to Living Forces, Ak. 1:8-16.

78.  I discuss this in chapters Three and Four below.