​Reid on Leibniz's Monad and the Conceptual Priority of the Whole

Reid on Leibniz’s Monad and the Conceptual Priority of the Whole Tamar Levanon, Bar Ilan University Forthcoming in The International Philosophical Quarterly Abstract: In his Essays on the Intellectual Powers of Man, Thomas Reid draws an analogy between his notion of the self and Leibniz’s notion of a monad. Reid formulates this analogy in order to highlight what he considers to be the essential feature of the self: its unified and indivisible structure. This paper considers Reid’s analogy in the specific context of the diachronic aspect of substantial unity. Its focus is specifically on the role that the idea of continuity plays in establishing the unity and indivisibility of the entities in question (viz., the self and the monad). As part of the ongoing debate over Leibniz’s mature metaphysics of substance, this paper further highlights the positive implication of Reid’s analysis of the self —which is usually viewed as a critical reaction to Locke and Hume—and its place within the early modern debate over the nature of substantial unity. Key words: Action; Continuity; Diachronic unity; Law of the series; Leibniz, G. W; Personal identity; Power; Reid, Thomas; Succession. I. Introduction: Reid’s appeal to Leibniz’s monad In his Essays on the Intellectual Powers of Man (1787), Thomas Reid draws the following analogy between his idea of the self (or of a person)1 and Leibniz’s notion of a monad: When a man loses his estate, his health, his strength, he is still the same person, and has lost nothing of his personality. If he has a leg or an arm cut off, he is the same person as he was before. The amputated member is no part of this person […] a person is something indivisible and is what Leibnitz calls a monad (EIP, 345; emphasis added). In an earlier chapter, Reid describes Leibniz’s monad as something “simple, without parts or figure”; Reid adds a few paragraphs later that “every monad is a complete substance in itself—indivisible, having no parts” (EIP, 307). It is therefore evident that Reid draws the analogy between his idea of the self and Leibniz’s monad in order to highlight the characteristic of indivisibility which he ascribes to the former. And to this end, Reid’s analogy is apt: indivisibility is clearly among the prominent features of the monad, as Leibniz himself made clear.2 Reid conceives of the self, like Leibniz’s monad, as decomposable and containing no parts. While considering the meaning of “personality” he writes: “it is sufficient for our purpose to observe, that all mankind place their personality in something that cannot be divided, or consists of parts. A part of a person is a manifest absurdity” (EIP, 345). 1 Motivated by Reid’s analogy, this paper focuses on Reid’s and Leibniz’s perspectives on the essential unity and indivisibility of a substance. More specifically, it suggests that Reid’s analogy be considered in the specific context of the diachronic aspect of the unity and indivisibility of the entities in question (viz., a person and a monad). This suggestion is motivated by the crucial role played by the diachronic aspect within Reid’s own thinking on the indivisible self in EIP. After drawing the analogy between the self and the monad, he writes as follows: “My personal, therefore, identity implies the continued existence of that indivisible thing which I call myself” (345; emphasis added). Reid is also sensitive to the diachronic aspect of Leibniz’s monad, defining it as that “which has within itself the power to produce all the changes it undergoes from the beginning of its existence to eternity” (EIP, 307). The emphasis that Reid places on the diachronic aspect of substantial unity, both in his own analysis of the self and in his references to Leibniz’s monad, invites us to consider the analogy he draws also in this specific context. In what follows, I consider Reid’s analogy while taking into account this specific aspect of substantial unity and I will primarily focus on the role played by continuity within Reid’s and Leibniz’s perspectives on substantial unity. While this paper is part of the extensive literature on Leibniz’s mature metaphysics of substance, my hope is that the suggested reading will also contribute to the debate over a relatively neglected theme in Reid’s analysis of the self and will relate it to more familiar topics (such as, for example, his philosophy of action). I am particularly interested in the positive implications of Reid’s analysis of the self and its place within the early modern debate over the nature of substantial unity. While most of the discussion of Reid’s analysis of the self is confined to its negative pole, that is, its being a backlash against Locke and Hume, it is his reference to Leibniz that functions as the catalyst for the current discussion. Alongside his sympathetic employment of the term “monad”, Reid also recognizes that his own analysis of substantial unity differs from that of Leibniz in some important respects. Focusing on the similarities and differences between the two schemes—as Reid understands them—makes it possible to capture the essence of his own perspective on substantial unity. The next section (§2) sets the stage for this discussion. It begins with Reid’s critique of the role played by interchangeability of being and one in Leibniz’s analysis of bodily extension. This is an appropriate point of departure since it uncovers Reid’s own perspective on the different senses in which the term “continuity” is used. It also reveals his understanding of Leibniz’s notion of a monad, which provides the foundation for the discussion (in §3) of the diachronic aspect of substantial unity in Leibniz’s mature metaphysics. 3 In clarifying this issue, special attention is focused on Leibniz’s employment of the law of the series in his correspondence with De Volder. Equipped with Leibniz’s view on continuity and its relation to substantial unity, in §4 I consider Reid’s attitude towards Leibniz’s metaphysics of substance and its place within the construction of his own scheme. The final section (§5) provides a concise synopsis of the relationship between Leibniz’s and Reid’s analyses of substantial unity. It also further explicates the essence of the kinship between them, which was understated by Reid. 2 II. “Every being is one” (omne ens est unum): Reid on Leibniz’s analysis of bodily extension In the chapter “Of Matter and of Space” in the second Essay of EIP, Reid writes that: “There is, indeed, a principle long received as an axiom in metaphysics […] that every being is one, omne ens est unum” (EIP, 323). Reid explains this principle as meaning “that everything that exists must either be one indivisible being, or composed of a determinate number of indivisible beings” (EIP, 323). Reid then turns to Leibniz’s endorsement of the principle. Indeed, it is Leibniz who provides one of the most celebrated formulations of the principle in a letter to Arnauld in which he states: “what is not truly one being is not truly one being either’” (April 30, 1687; AG, 86).4 Reid, whose attention in the opening of this chapter is focused on the nature of bodily extension, explains that it is the fact that matter is composed of “simple and indivisible substances” which, according to Leibniz, grounds it as something real (EIP, 323). However, Reid’s reference to the functioning of the interchangeability of being and oneness in Leibniz’s account of bodily extension is critical rather than complimentary. Reid reports that, in view of the dubious metaphysical origin of this principle, he himself is not at all convinced by it.5 Rather, Reid accepts the infinite divisibility of matter as a more tenable position, explaining that if bodies are made up of individual unextended units, this would yield one of two possible, yet equally absurd, consequences. In this case “either we have come by division to a body which is extended, but has no parts, and is absolutely indivisible; or this body is divisible, but, as soon as it is divided, it becomes no body” (EIP, 323).6 Later on, Reid elaborates: To suppose bodies organized or unorganized, to be made up of indivisible monads which have no parts, is contrary to all that we know of body. It is essential to a body to have parts; and every part of a body is a body, and has parts also. No number of parts, without extension or figure, not even an infinite number, if we may use this expression, can, by being put together, make a whole that has extension and figure, which all bodies have (EIP, 308). Evidently, Reid agrees with Leibniz that what lacks parts must also lack extension, but, as evident from the above passage, he denies that the extended is entailed by the unextended. The demarcation between the two realms implies not only that an amalgamation of unextended elements is incapable of creating extension, but also that every part of an extended magnitude (whether bodily, spatial or temporal) must itself be extensive and thus that extension is infinitely divisible (EIP, 323). Due to its infinite divisibility, extension is characterized as continuous. Reid emphasizes this point by means of his distinction between extension and number. Although he defines both extension (whether spatial or temporal) and number as “the measures of all things subject to mensuration”, it is only a number which is considered to be a discrete quantity, “because it is compounded of units, which are all equal and similar, and it can only be divided into units” (EIP, 342). “Duration and extension” on the other hand, “are not discrete but continued quantity. They consist of parts perfectly similar, but divisible without end” (EIP, 342). Notice that this type of continuity, which Reid ascribes to extensive magnitudes, is quite different from the type of 3 continuity he ascribes to the self. Reid clearly employs the idea of continuity to imply both the infinite divisibility of extension and the indivisibility of substantial self. In short, Reid distinguishes between: 1) Discrete quantities, such as numbers, which are determinately divisible according to their basic units. 2) Continuous magnitudes, such as temporal, spatial or bodily extension, which are infinitely divisible (though sometimes they are thought of as discrete due to their measurability using numbers).7 3) Continuity in the sense of unity and indivisibility which reflects the intuitive understanding of the continued existence of ourselves. William James describes this sense of continuity in his Principles of Psychology as “that which is without breach, crack, or division” (1890, 237). It is also clear that in both discussions, i.e. of personal identity and bodily extension, Reid highlights the indivisibility of the monad as its distinctive feature. Reid understands “indivisibility” as implying a metaphysical unity, explaining that Leibniz’s endorsement of the equivalence of being and one is meant to show that “all beings must have this metaphysical unity” (EIP, 323). In “On Oneness and Substance in Leibniz’s Middle Years” (2015), we defended such a reading of Leibniz’s recurring statements concerning the interchangeability of being and one (as implying the essential unity and indivisibility of substance).8 The defense was based on the parallel between Leibniz’s view of numbers and his view of substance. In the realm of mathematics, as we noted, Leibniz regards “one” not as a number but as a unit which is the foundation of all numbers. In the same vein, Leibniz regards the unity of simple substances as the foundation of all plurality. Notice moreover that the idea of a derivative plurality (whose foundation is a unit) is bilateral, involving external and internal sides. This duality is hinted at by Reid in his reference to the common usage of the term “number”. “In arithmetic,” Reid writes in EAP, “the word number among the ancient, always signified so many units; and it would have been absurd to apply it either to unity or to any part of an unit, but now we call unity, or any part of unity, a number” (606). Returning to the role that the analogy between arithmetical and metaphysical units plays within Leibniz’s scheme, we can conclude that, like an arithmetic unit, a metaphysical unit is the basis for both external and internal complex structure. While our earlier paper focused on the external type of complexity (aggregates), the following section focuses on the internal type of complexity (which specifically expresses the diachronic aspect of substantial unity).9 This discussion extends our earlier paper in that it provides an additional perspective on the parallel between the role played by the idea of a unit in mathematics and the role it plays in metaphysics. Furthermore, it provides the basis for the subsequent discussion of the relationship between Leibniz’s and Reid’s analyses of the diachronic aspect of substantial unity. III. Leibniz on the conceptual priority of the whole and the law of the series Already at the beginning of Monadology, Leibniz emphasizes that the simplicity of the monad is compatible with it having an internal complex structure. Even though a monad lacks parts (and thus cannot be divided), it is 4 qualitatively complex. “[T]here must be diversity [un détail] in that which changes” asserts Leibniz in §12 of the Monadology, adding in the subsequent section that “this diversity must involve a multitude in the unity or in the simple. For, as every natural change is produced by degrees, something changes and something remains. As a result, there must be a plurality of properties [affections] and relations in the simple substance, although it has no parts” (Monadology §13; AG, 214; emphasis added). The parallel between the arithmetical and metaphysical units is again employed, this time for the purpose of clarifying the relation between unity and its internal complex structure. In a letter to Louis Bourguet, Leibniz refers to the internal complexity of an arithmetical unit as follows: When I say that unity is not further analyzable I mean that it cannot have parts whose concept is simpler than it. Unity is divisible but not resolvable, for fractions, which are parts of unity, have less simple concepts than whole numbers, which are less simple than unity, since whole numbers always enter into the concept of fractions. Many who have philosophized about the point and about unity in mathematics have become confused by failing to distinguish between analysis into concepts and division into parts. Parts are not always simpler than wholes, though they are always less than the whole (August 5, 1714, L, 664-5; emphasis added) This passage implies that although an arithmetical unit can be divided into fractions, it is not reducible into fractions. Unity is presupposed by any of its fractions and therefore it is simpler in the sense that, although fractions are the products of the division of a unit, the unit itself is not a product of their combination. Thus, a unity can be the object of analysis, but not of real disintegration into parts. And since the idea of a fraction already supposes that of an original unit, it cannot be regarded as basic or as constitutive. The fact that parts of a mathematical magnitude do not have a constitutive role has usually been discussed by Leibniz scholars in relation to the ideal nature of mathematical magnitudes and in contrast to the determinate division of other phenomena in which unities are prior to multitudes (such as, for example, a bodily extension). It is typically emphasized that while ideal things are “composed as a number is composed from fractions”, actual things, which involve a determinate division, are “composed as a number is composed from unities” (January 19, 1706; LDV, 333). In an earlier letter to De Volder, Leibniz explains: From the fact that mathematical body cannot be resolved into primary constituents, it may be inferred that it is certainly not real, but something mental, designating nothing other than the possibility of parts, not something actual. Indeed, a mathematical line is like an arithmetical unity, and in both cases the parts are only possible and absolutely indefinite. And a line is no more an aggregate of the lines into which it can be cut up, than a unity is an aggregate of the fractions into which it can be broken up (June 30, 1704; LDV, 303). However, in the above passage from the letter to Louis Bourguet, Leibniz does not focus on the ideal nature of arithmetical unities or of mathematical magnitudes in general. His main point is rather that an arithmetical unity is not resolvable into its constitutive elements, not because they are indeterminate, but because they are conceptually dependent upon it. The crucial point is that a unity is conceptually prior to the infinity of elements that comprise it. In the case of an arithmetical unit, this means that the concept of the whole unit is already contained in the concept 5 of fractions rather than the other way around. Thus, the whole unit does not result from combining the fractions together but rather is presupposed by them. Moreover, in one of his letters to De Volder, Leibniz extends this perspective on the conceptual priority of unity over its elements to substances as well, claiming that substances are not “wholes that contain parts formally, but total things that contain partial things eminently” (January 21, 1704; LDV, 289).10 In his correspondence with De Volder, Leibniz expresses the diachronic aspect of substantial unity, viz., its conceptual priority over its successive elements, by means of the law of the series. In both mathematical and metaphysical contexts, the law of the series confronts the question of how a multiplicity (or even an infinity) of states can be reconciled with the idea of a fundamental unity. The answer is given in terms of the dependency between the elements in the series and therefore between each element and the series viewed as a whole. In the realm of mathematics, this law is viewed as a formula that determines an ordered relation between each step in the series; in the metaphysical realm, it is viewed as a single internal law that determines the continued unfolding of successive states of a simple substance. Subsequent to the abovementioned quote from the letter to De Volder, Leibniz writes as follows: The substance that succeeds is taken to be the same as long as the same law of the series, i.e., of the continual simple transition, persists that gives rise to our belief in the same subject of change, i.e., the monad. I say that the fact that there is a certain persisting law, which involves the future states of that which we conceive as the same, is the very thing that constitutes the same substance (January 21, 1704; LDV, 291). There are two points to be made with regard to this passage: the first concerns the sense in which the law of the series is meant to provide unity, while the second relates to the type of continuity that the law provides. Leibniz’s phrasing of the law—“I say that the fact that there is a certain persisting law […] is the very thing that constitutes the same substance” [id ipsum est quod substantiam eandem constituere dico]—explains why it has been habitually treated by scholars as a unifying factor. Loemker comments on Leibniz’s statement that substances are not “wholes that contain parts formally, but total things that contain partial things eminently”, by saying that it is the law which shows that the whole is not “merely the aggregate of its parts” but “a unity which possesses reality beyond these changing modes themselves” (L, 541). Fleming simply states that the law of the series “unifies the series of perception by determining or explaining the progress of the series” (1987, 84; emphasis added). But the employment of the term “unifies” does not suggest that the law’s functioning is to combine separate elements. Rather, as implied by the passage from Leibniz’s letter to Louis Bourguet, the law of the series expresses the conceptual priority of substantial unity over the infinite multitude (i.e. the series of successive perceptual states) that it implies. The only sense in which the law of the series unifies a substance is thus in the sense of “holding up” its internal complexity, while at the same time preserving its oneness. As Leibniz writes in a draft of his letter to De Bosses, “[…] the operation proper to the soul is perception, and the nexus of perceptions, according to which 6 subsequent perceptions are derived from previous ones, forms the unity of the perceiver” (April 30, 1709; LDB, 129). The role played by the law of the series in expressing the unity of substance further explains why it has sometimes been identified by commentators with the idea of substantial form and even with the whole substance itself.11 The second point relates to the above passage from Leibniz’s letter to De Volder (dated June 30, 1704) in which he highlights the indeterminate nature of the division of ideal magnitudes (arithmetical unities). It is due to this feature that ideal magnitudes (e.g., ideal space, time, and motion) are considered to be continuous in the strong mathematical sense. However, in his correspondence with De Volder Leibniz employs the law of the series to express another type of continuity, which is consistent with a definite division into real parts (viz., the elements of the series).12 Leibniz uses the law of the series in the correspondence to express something other than an indefinite division.13 The phrase he uses, i.e. “continual simple transition”, denotes a more intuitive sense of continuity which relates to the smooth and uninterrupted unfolding of monadic states and the absence of any gap between them. Clearly, by the law of the series Leibniz hoped to express not only the conceptual priority of substantial unity over its successive states but also the dynamic nature of their unfolding. This effort reaches culmination in the following paragraph in which Leibniz associates the law of the series with primary active force: “But the persisting thing itself, insofar as it involves all cases, has primitive force, so that primitive force is like the law of a series, and derivative force is like a determination that designates some term in the series” (January 21, 1704; LDV, 287; emphasis added).14 Leaving aside the question of whether Leibniz is successful in expressing the dynamic implications of the law of the series, it is evident that this idea is pivotal in his defense of substantial action.15 It is in fact the question of the possibility of substantial action that prompted the discussion of the law of the series in the first place. The debate originates from Leibniz’s characterization of action in terms of an “internal tendency to change” (November 19, 1703; LDV, 279), which although not proven by experience (January 21, 1704; LDV, 293) is nevertheless demonstrated by it. This tendency is experienced “from the inside”, Leibniz adds, “where the operations of the mind themselves exhibit changes” (November 19, 1703; LDV, 279). De Volder challenges this characterization of action by arguing that “whatever follows from the nature of a thing is in the thing in an invariant way and cannot be removed from it certainly as long as the nature of the thing remains the same, since there is a necessary connection between it and the very nature of the thing” (October 30, 1703; LDV, 273; emphasis added). In other words, things cannot be the source of their own series of changes, and action is only possible if it “is always of exactly the same kind, and so does not lead to any change in the thing that is acting” (January 5, 1704; LDV, 283; emphasis added). Leibniz evokes the idea of the law of the series in response to De Volder’s characterization of action and in order to sharpen the sense in which action is indeed “the same”. Leibniz’s answer to De Volder is based on the distinction between a thing’s permanent properties and its transitory modifications (November 19, 1703; LDV, 279). That there is such a law is evident from the modifications themselves because “every modification 7 presupposes something lasting” (June 20, 1703, LDV, 263), and again, “everything accidental, i.e., mutable, must be a modification of something essential, i.e., perpetual” (June 30, 1704; LDV, 307). The permanent element is the law itself, such that “nothing is permanent in things except the law itself which involves a continuous succession” (January 21, 1704; LDV, 289). Leibniz already makes this point (i.e. if a substance continues to follow the same law, this does not mean that it exhibits the same action) in his response to Bayle’s reservations concerning the idea of a pre-established harmony: I have compared the soul with a clock only in respect of the ordered precision of its changes, which is imperfect even in the best clocks, but which is perfect in the works of God […] when it is said that a simple being will always do the same thing, a certain distinction must be made: if ‘doing the same thing’ means perpetually following the same law of order or of continuation, as in the case of certain series or sequence of numbers, I admit that all simple beings, and even all composite beings, do the same thing; but if ‘same’ means acting in the same way, I don’t agree at all (1698; WF, 206). Therefore, the only sense in which a substance is always the same is that of being dominated by the same rule. This dominance of “the same rule” does not imply the uniformity of action, but only the conceptual priority of substantial unity over its successive elements. This priority is formulated, moreover, in terms of a unique type of continuity, the “simple transition” from one monadic state to another. IV. Reid on the continued existence of the substantial self16 Reid frequently emphasizes the diachronic aspect of substantial unity, viz. its continued existence. His claim (already cited in §1) that “personal identity implies the continued existence of that indivisible thing which I call myself” is entailed by his general characterization of “identity” in terms of continued existence. “If you ask a definition of identity”, Reid writes, “I confess I can give none, it is too simple a notion to admit of logical definition” (EIP, 344). The only thing that can be affirmed with regard to identity is: […] that identity supposes an uninterrupted continuance of existence. That which hath ceased to exist, cannot be the same with that which afterwards begins to exist; for this would be to suppose a being to exist after ceased to exist […] Continued uninterrupted existence is therefore necessarily implied in identity” (EIP, 344; emphasis added). Continuity is not only essential for the numerical sameness of the self, it applies only in this particular case. Only the identity of persons can be considered perfect, in the sense that the identical subject does not change (EIP, 345). It is precisely indivisibility that renders change impossible: since a person has no parts, and since change presupposes the existence of parts, a person cannot change. It is in this context (viz., the lack of parts) that Reid evokes Leibniz’s monad once again: “it is impossible that a person should be in part the same and in part different, because a person is a monad and it is not divisible into parts” (EIP, 345). It is thus Reid’s agreement with Leibniz on the indivisibility of a substance that leads them to diverge on the possibility of qualitative change. 8 Moreover, Reid holds that the indivisibility of substance (which necessarily implies a denial of change) imposes a two-layer structure in which the boundary between the unchanging substance and the series of changes that it is said to involve is preserved. Reid’s strategy to distinguish between the continued and uninterrupted existence of the self and the successive series of its operations is consistent with his idea that only things which have a continued existence can ground our own identity.17 The successive and fleeting operations of the mind cannot constitute the identity of a person, but rather illustrate that the substantial self must be there, as their bearer. It is thus the conceptual priority of continuity over succession that underlies Reid’s endorsement of the substratum view of substance. The relation between the self and its successive operations is thus that of belonging. When I think about the operations of the mind, I must think of them as mine, viz., as related to the underlying self. As Reid writes: Whatever this self may be, it is something which thinks, and deliberates, and resolves, and acts, and suffers. I am not thought, I am not action, I am not feeling; I am something that thinks, and acts, and suffers. My thoughts, and actions, and feelings, change every moment—they have no continued, but a successive existence; but that self or I, to which they belong is permanent and has the same relation to all succeeding thoughts, actions and feelings, which I call mine (EIP, 345; emphasis added).18 Throughout his analysis of personal identity in the third essay of EIP, Reid does not elaborate on the question of what exactly the relation of belonging consists of. As Reid already explains in the first Essay, this relation, like other notions in his empiricism of common sense, is considered to be something simple and unanalyzable. It is given to us as part of immediate experience as the essential companion of the operations themselves: “there are some things which cannot exist by themselves, but must be in something else to which they belong, as qualities or attributes […] In like manner, the things I am conscious of, such as thought, reasoning, desire, necessarily suppose something that thinks, that reasons, that desires” (EIP, 43). Nevertheless, despite it being an ultimate notion, the relation between the self and its operations may be further clarified in light of Reid’s discussion of the “train of thought” in the fourth Essay in EIP. It is here, in the context of “the consciousness that we have of the succession of thoughts which pass in our minds” (EIP, 379), that Reid confronts our experience of diversity and succession. Reid’s analysis of our train of thought is closely related to his criticism of the theory of ideas (according to which the operations of the mind somehow combine themselves, without the aid of an external agent).19 Leaving aside this negative aspect of Reid’s analysis of the train of thought, the remainder of the section focuses on its contribution to clarifying the diachronic aspect of substantial unity. Of particular relevance to our current discussion is Reid’s idea of a regular train of thought. Thus, “by a regular train of thought, I mean that which has a beginning, a middle, and an end, an arrangement of its parts according to some rule” (EIP, 383; emphasis added). It is this feature (rather than that of the substantial self), that naturally evokes the unfolding of the Leibnizian monad according to its own law. Reid himself is aware of this 9 association. Immediately after mentioning the “order, connection and unity” of the experienced succession of thoughts, he asks: “how is this regular arrangement brought about”? […] shall we believe with Leibnitz, that the mind was originally formed like a watch wound up; and that all its thoughts, purposes, passions, and actions, are effected by the gradual evolution of the original spring of the machine, and succeed each other in order, as necessarily as the motions and pulsations of a watch? If a child of three or four years put to account for the phenomena of a watch, he would conceive that there is a little man within the watch, or some other little animal, that beats continually, and produces the motion. Whether the hypothesis of this young philosopher, in turning the watch spring into a man, or that of the German philosopher, in turning a man into a watch spring, be the most rational, seems hard to determine” (EIP, 382). This is not the first time that Reid refers to Leibniz’s portrayal of the soul in terms of a watch. Earlier in the Essays, while surveying Leibniz’s mature philosophy, Reid lingers on the role that this portrayal plays within Leibniz’s system of the pre-established harmony. According to Reid, it is by means of this scheme that Leibniz expresses the synchronization among all substances: “just as one clock may be so adjusted as to keep time with another, although each has its own internal moving power, and neither receives any part of its motion from the other” (EIP, 308). Previously in the chapter, Reid emphasizes the importance of the idea of internal power in his description of Leibniz’s monad as that “which has within itself the power to produce all the changes it undergoes”; these changes are “only the gradual and successive evolutions of its own internal powers” (EIP, 307). Considering the crucial role that the idea of internal power plays within Reid’s own thinking on the regular arrangement of the successive series, it is not surprising that his attention is drawn to this aspect of Leibniz’s account of a monad. It is in fact Reid’s criticism of the Leibnizian account of internal power that is the key to understanding his own perspective on the diachronic aspect of substantial unity. While there is an extensive literature on Reid’s philosophy of action and his notion of power, the scope of the following discussion is carefully confined. It focuses only on those aspects of Reid’s notion of power that emerge from his critique of Leibniz and which help to illustrate his own perspective on substantial unity. Reid explicitly states his dissatisfaction with one crucial consequence of Leibniz’s idea of a priori programming of the individual substance, namely that it renders its train of perception indifferent to external reality. This is because “we do not perceive external things because they exist, but because the soul was originally so constituted as to produce in itself all its successive changes, and all its successive perceptions, independently of the external objects” (EIP, 308). However, the detachment from external reality is just one problematic consequence of the idea of a priori programing, which itself resulted from the misunderstanding of the idea of activity.20 The gist of Reid’s criticism is that pre-established programming abolishes the subject’s ability to exert or to “bring about” its own series of changes and thus renders the idea of action (and of perception) empty. “I cannot undertake to reconcile this part of the system”, Reis writes, referring to Leibniz’s pre-established harmony, “with what was 10 before mentioned —to wit, that every change in a monad is the evolution of its own original powers” (EIP, 307). To clarify this point, recall the role of the will in the exertion of power within Reid’s system: “power to produce any effect, implies power not to produce it” (EAP, 523). The dependency of change “upon the power and will of its cause” (EAP, 523) implies the contingency of change and rules out Leibniz’s perspective. A subject that follows its predetermined (and necessary) series of changes is simply not active in the full sense of the word. The focal point is that Reid’s account of change relies on a principal distinction between the cause of change (viz., the action or the exertion of power) and the change itself. “[T]hat which produces a change by the exertion of its power we call the cause of that change; and the change produced, the effect of that cause” (EAP, 515). This is precisely why power, which itself cannot be defined, is relative. Its existence is revealed to us through the experienced change that it produces. This distinction between the cause of change and the change itself does not suggest that the cause must be external to the changing thing. Indeed, it is our experience of ourselves as the internal causes of our own actions and thoughts that provides us with the idea of activity. Thus, “from the consciousness of our own activity, seems to be derived not only the clearest but the only conception we can form of activity, or the exertion of active power” (EAP, 523). In order for us to have the idea of a cause of change, it is necessary that we experience ourselves as the internal source of a series of changes, yet as distinct from it. The focal point of Reid’s dissatisfaction with Leibniz’s notion of internal power is that it blurs the distinction between the series of changes and its cause (viz., action). By itself, a series of changes (and even a regular one, as Leibniz suggests) “could never lead us to the notion of a cause” (EAP, 523). We are now in a better position to understand the relation between the self and its operations. The “belonging” in question expresses the dependency of each element in the successive series on the action of a regulative principle. This principle must, by its nature, be external to the series—it cannot be a part of it nor can it be identical to it. Thus, according to Reid, the self may exert its power although it does not actually change throughout this action (exertion). This primordial activity constitutes change, although it is not, in itself, change. In an earlier essay on Aristotle’s Categories, Reid’s attention is drawn to this structure, as shown by the following comment: “the most remarkable property of substance is, that one and the same substance may, by some change in itself, become the subject of things that are contrary” (AL, 685). Reid’s own account transforms “change in itself” into the idea of primordial action, which is distinct from the change that it produces.21 The successive series is dependent upon the action of the self not only with respect to its progression, but also with respect to its unity. Again, the point is that only something which is distinct from the series can unify its elements. As formulated by Reid, the power to distinguish unities from aggregates “is connected with all regular trains of thoughts, and may be the cause of them” (EIP, 383). Thus, the ability to recognize the series as a unity is itself the reason for its being a unity. In contrast to the metaphysical unity of the self, the unity of the “continued succession of thought” (EIP, 379) is derivative and involves judgment.22 Reid expresses this dependency of the aggregate on the unity that it is based on in his discussion of the manner in which we gain our notion of relations 11 (“belonging” included) when he writes that: “the notions of unity and number are so abstract, that it is impossible they should enter into the mind until it has some degree of judgment […] every number is conceived by the relation which it bears to unity, or to known combinations of units” (EIP, 421). V. Concluding Remarks This paper derives Reid’s perspective on substantial unity by synthesizing his sympathetic attitude towards Leibniz’s notion of a monad (viz., its indivisibility) with other, less sympathetic remarks regarding the same notion (which relate to its internal power). It is the confluence of these two issues—unity and action—that emerges from Reid’s sporadic references to Leibniz and illuminates his own perspective on substantial unity. This section concludes by emphasizing the common motivation of both analyses, a kinship which was understated by Reid himself. But let us first summarize the crux of the difference, as it emerges from Reid’s references to Leibniz. In general, Reid’s discomfort with Leibniz’s analysis of substantial unity can be seen from his interpretation of the idea of belonging, viz., the relation between substantial unity and the successive series that it is said to incorporate. In Reid’s view, “belonging” implies that a substance is distinct from the successive series that it generates. Obviously, the states of the monad do not belong to it in that same sense. Rather, in the case of the monad, there is only the continuous unfolding of the monadic states, which is simply the monad itself. And since there is nothing beyond this process of unfolding, the states of the monad do not strictly “belong” to it. It is preferable to view the continued unfolding of successive states as the transitory aspect of the same permanent principle. This structural dissimilarity also reflects a difference in perspective on the nature of a simple substance’s action. While Leibniz defines action as an internal tendency towards change, thus allowing for an internal qualitative complexity to support this tendency, Reid argues that simplicity necessarily entails the exclusion of change. Reid then insists on a sharp distinction between action and change which implies that although change must be the outcome of a substance’s action it cannot be presupposed by it. This distinction, which is of course parallel to that between a substance and its successive series, plays a crucial role in Reid’s account of free agency. To understand the idea of action in terms of a programed series of changes is, according to Reid, to render this idea meaningless. What bothers Reid is the blurring of the boundary between the active substance and the series of changes that it produces. This criticism is solid, yet it ignores the intimate relationship between the two perspectives on the role of action which I shall conclude with. Both Leibniz and Reid highlight the dependency of every item in the successive series upon a permanent regulative principle. This dependency implies that the regulative principle has a conceptual priority over its elements: the idea of a whole unified substance is already contained in (and is the necessary condition for) each and every element in the series. In other words, this principle functions as the metaphysical foundation that supports the successive series and which is presupposed by its progression. That it is the same principle which is being exemplified by each and every element of the series implies the unity of the series. However, the regulative principle 12 implies more than just unity, as highlighted by both Leibniz and Reid. It further shows that in explaining diachronic unity both lean heavily on the idea of action. This is why both Leibniz and Reid explain the regulative principle in terms of a unique type of continuity, different from that which is ascribed to extension, and which should be understood more intuitively as implying an uninterrupted flow. In fact, both Leibniz and Reid argue that there cannot be a unified process of change unless there is a primordial kind of action at a deeper level that constitutes it. It is this point that Leibniz expresses in “Nature Itself” and which brings him closer to Reid: “[T]here can be no action [actio] without a force for acting, and, conversely, a power [potentia] which can never be exercised is empty” (AG, 160). In sum, the differences between the two systems, and in particular those which result from Leibniz’s pre-established harmony and which are indeed crucial within the scope of Reid’s account of free agency, do not overshadow a similar attitude towards the metaphysical importance of activity in explaining substantial unity and the series of changes it involves. Notes As in Reid’s discussion in chapter 4 of the third Essay in EIP, the terms “self” and “person” are used interchangeably. Already in the opening paragraph of the Monadology, Leibniz characterizes the monad as “nothing but a simple substance […] simple, meaning without parts” (§1). Earlier, in a letter to De Volder, he asserts that: “when I say that every substance is simple, I understand by this that it lacks parts” (April, 1702; LDV, 239). 3 As I explain in §2, the following discussion of the diachronic aspect of substantial unity in Leibniz’s metaphysics is motivated by a previous paper (Nachtomy and Levanon, 2015) and attempts to add an additional layer to it. 4 Sixteen years later, in a letter to De Volder, Leibniz reaffirms that, “if there is nothing that is truly one, then every true thing will be eliminated” (June 20, 1703; LDV, 263). 5 Reid express his reservations about the adequacy of metaphysical inquiry in the following paragraph: “A remarkable deviation from [the common sense] arising from a disorder and in the constitution is what we call lunacy […] when a man suffers himself to be reasoned out of the principles of common sense, by metaphysical arguments we may call this metaphysical lunacy; which differs from the other species of the distemper in this that it is not continued but intermittent: it is apt to seize the patient in solitary and speculative moments; but when he enters into society, common sense recovers her authority” (EIP 209). 6 Cf. Cummins’ comparative discussion of the composition of extension in Bayle, Leibniz, Hume and Reid (1990). 7 As Reid explains, we give names to portions of duration (such as a day or an hour) and after fixing those terms as units we use them to measure duration. A number is therefore the common measure of duration and extension, although they are continuous rather than discrete (EIP, 343). 8 This defense is part of the general debate over the proper understanding of the term “one” in Leibniz’s metaphysics. It is in contrast to the view that emphasizes the numerical sense of “one”, rather than that of a metaphysical unity. 9 The relation between a simple substance and its internal succession of phases is one manifestation of the general problem of the one and the many that occupied Leibniz. For a discussion of this specific manifestation of the problem, see Whipple (2010). 10 Leibniz makes this claim while comparing his own pluralistic metaphysics of substance to Spinoza’s monism and after pointing out that Spinoza “could have acknowledged something analogous to what he somehow granted to the whole universe in all of the parts” (January 21, 1704; LDV, 289). 11 Cf., Whipple (2010, 393); Hillman (2009, 120); Phemister (2005, 195; 122); Cover and O’Leary-Hawthorne (1999, 224). The identification between the law of the series and the idea of substantial form is also consistent with Arthurs’ reading of the latter as that which does its work “by giving a teleological and functional unity over time, a diachronic rather than a synchronic unity” (2011, 92; emphasis added). 12 Leibniz writes: “But in real things, namely, bodies, the parts are not indefinite (as they are in space, a metal thing)but are actually assigned in a certain way, in accordance with the divisions and subdivisions that nature actually institutes according to different motions” (June 30, 1704; LDV, 303). 1 2 13 13 While continuity proper means infinite division into indeterminate parts, the series of monadic states is continuous in the sense of being dense (see Anapolitanos (1999, 151; 117); Crocket (1999, 135)). 14 For the identification between the law of the series and the idea of primitive force see Adams (1994, 80). 15 The question of whether Leibniz is indeed successful in expressing the dynamic implication of the law was raised by De Volder himself. He writes that “in laws of series […] all the terms are contained in the very nature of the series in a unique and invariant way and nothing successive can be conceived of in that” (January 5, 1704; LDV, 283). Paul Lodge reformulates De Volder’s criticism in the introduction to the correspondence, arguing that the law merely “encapsulate atemporal structures rather than determining successive states” (LDV, lxxxviii). Donald Rutherford argues in his “Leibniz on Spontaneity”, that Leibniz’s suggestion that the law of the series is to be thought of in terms of a real substantial power instead of a mere static formula does not hold water “for it is characteristic of such a power qua law that it is perpetual and unchanging; it is that which ‘contains’ all the particular changing states of the substance. Although such an unchanging ground is presupposed by change, it does not explain change” (2005, 165). 16 For a broader perspective on Reid’s analysis of this theme, see Levanon’s “Thomas Reid and the Evolution of the Idea of the Specious Present” (2016) and Yaffe’s “Beyond the Brave Officer” (2010). 17 See Levanon (2016) and also Yaffe: “the distinction between continuous and successive existence, and the companion distinction between strict and derived identity, mark a distinction between true unity and its absence” (2010, 175). 18 Reid further writes that “by attending to the operations of thinking, memory, reasoning, we perceive or judge, that there must be something that thinks, remembers, and reasons which we call the mind” (EIP, 422). 19 Reid complains that, according to Hume, “what we call a mind is nothing but a train of ideas connected by certain relations between themselves” (EIP, 299; also see 464). 20 Cf. Gallie’s book in which he emphasizes throughout that “Reid’s insistence that perception is an act of the mind and not a passive reaction to one’s surroundings” (1998, x). 21 For a discussion of the difficulties entailed by Reid’s contention “that we are the efficient causes of some of our bodily movements and of some of our directions of thought”, see Yaffe (2004). 22 Notice the unusual coupling of continuity and succession which hints at the relative degree of unity provided by the substantial self to the successive series of operations. REFERENCES Leibniz’s writings AG G. W. Leibniz, Philosophical Essays, ed. and trans. by R. Ariew and D. Garber (Indianapolis: Hackett, 1989). L Leibniz, G. Philosophical Papers and Letters, ed. and trans. by L. Loemker (Dordrecht: Reidel, 1969). LDB The Leibniz-Des Bosses Correspondence, ed. and trans. by B. C. Look and D. Rutherford (New Haven: Yale University Press, 2007). LDV The Leibniz-De Volder Correspondence: With Selections from the Correspondence between Leibniz and Johann Bernoulli, ed. and trans. by P. Lodge (New Haven: Yale University Press, 2013). WF G. W. Leibniz: Philosophical Texts, eds. R. Francks and R. S. Woolhouse (Oxford: Oxford University Press, 1998). Reid’s writings EIP Essays on the Intellectual Powers of Man, in The Works of Thomas Reid, Collected, with Selections from his Unpublished Letters. Preface, Notes, and Supplementary Dissertations by Sir William Hamilton. Vol. 1. (Edinburgh: Maclachlan and Stewart, 1787/1853). EAP Essays on the Active Powers of Man, in The Works of Thomas Reid, Collected, with Selections from his Unpublished Letters. Preface, Notes, and Supplementary Dissertations by Sir William Hamilton. Vol. 2. (Edinburgh: Maclachlan and Stewart, 1788/1853). AL A brief Account of Aristotle’s Logic, in The Works of Thomas Reid: Fully Collected, With Selections from his Unpublished Letters. Preface, Notes and Supplementary Dissertation by Sir William Hamilton. Vol 2. (Edinburgh: Maclachlan and Stewart, 1774/1853). Other sources Adams, R. M. (1994). Leibniz: Determinist, Theist, Idealist. Oxford: Oxford University Press. Anapolitanos, D. A. (1999). Leibniz: Representation, Continuity and the Spatiotemporal. Dordrecht: Klower Academic Publishers. Arthur, R.T.W. (2011). “Presupposition, Aggregation, and Leibniz’s Argument for a Plurality of Substances,” The Leibniz Review, 21: 91-115. 14 Cover, J. A. & O’Leary-Hawthorne, J. (1999). Substance and Individuation in Leibniz. Cambridge: Cambridge University Press. Crockett, T. (1999). “Continuity in Leibniz’s Mature Metaphysics.” Philosophical Studies 94: 119-138. Cummins, Phillip. (1990). “Bayle, Leibniz, Hume and Reid on Extension, Composites and Simples,” History of Philosophy Quarterly, 7(3): 299-314. Fleming, N. (1987). “On Leibniz on Subject and Substance,” The Philosophical Review, 96(1): 69-95. Gallie, R. D. (1998). Thomas Reid: Ethics, Aesthetics and the Anatomy of the Self. Dordrecht: Springer. Hillman, T. Allan. (2009). “Substantial Simplicity in Leibniz: Form, Predication, & Truthmakers,” The Review of Metaphysics, 63(1): 91-138. James, William. (1890). The principles of Psychology. Vol. 1. New York: Dover Publications. Levanon, Tamar & Nachtomy, Ohad. (2015). “Oneness and Substance in Leibniz’s Middle Years.” The Leibniz Review, 24:6991. Levanon, Tamar. (2016). “Thomas Reid, William James and the Evolution of the Idea of the Specious Present,” History of Philosophy Quarterly, 33(1): 43-61. Lodge, Paul. (2013). “Introduction” in P. Lodge, (ed.), The Leibniz- De Volder Correspondence, New Haven: Yale University Press: xxiii-ci. Phemister, P. (2005). Leibniz and the natural world. Dordrecht: Springer. Whipple, John. (2010). “The Structure of Leibnizian Simple Substances,” British Journal for the History of Philosophy 18(3): 379-410. Rutherford, D. (2005). “Leibniz on Spontaneity,” in Donald Rutherford & J. A. Cover (eds.), Leibniz: Nature and Freedom. Oxford: Oxford University Press, pp: 156-180. Yaffe, Gideon. (2010). “Beyond the Brave Officer: Reid on the Unity of the Mind, the Moral Sense and Locke’s Theory of Personal Identity,” in Sabine Roeser (ed.), Reid on Ethics. Palgrave Macmillan UK, pp: 164-183. Yaffe, Gideon. (2004). Manifest Activity: Thomas Reid’s theory of action. Oxford: Oxford University Press. 15