From theism to idealism to monism: a Leibnizian road not taken


This paper explores a PSR-connected trail leading from theistic idealism to a form of substance monism. In particular, I argue that the same style of argument available for a Leibnizian form of metaphysical idealism actually leads beyond idealism to something closer to Spinozistic monism. This path begins with a set of theological commitments about the nature and perfection of God that were widely shared among leading early modern philosophers. From these commitments, there arises an interesting case for metaphysical idealism, roughly the thesis that only minds and mind-dependent states actually exist. However, I contend, that same theistic reasoning also leads to an idealist form of substance monism, the view that God is the only actual substance and that almost everything else is merely an intentional object in God’s mind.

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  1. 1.

    It will not be exactly Spinoza’s form of monism for many reasons, the most important being that it denies that extension is a fundamental attribute of God. There is a long history of suspecting that Leibniz doth protest too much against various Spinozistic conclusions, including substance monism. For previous discussions of somewhat related pressures towards Spinozistic monism in Leibniz, see Adams (1994, pp. 123–134), Kulstad (1994), and Mercer (2001, p. 453–55). Cover and O’Leary-Hawthorne (1999, p. 253–289) suggest that Leibniz’s views on harmony might actually help him avoid one strand of monistic pressure, whereas I will suggest that Leibniz’s account of harmony actually increases the pressure towards monism.

  2. 2.

    See also a similar charge against the authors of the second set of objections (1641; CSM II/99) and Descartes’ complaint to an unknown correspondent in 1642 (CSMK III/212).

  3. 3.

    Bayle (1707) repeatedly states and responds to Le Clerc’s charge in his Dialogues of Maximus and Themistius. Leibniz (1710; T 266) repeats Bayle’s objection to Jacquelot from God’s perfection, and then argues against it—as well as against what Leibniz describes as the same objection by Arnauld against Malebranche!

  4. 4.

    This is true even proleptically of Descartes (1644; CSM I/200–201).

  5. 5.

    See, for example, Leibniz 1710; G VI/439. God’s self-dependence was seen as more or less problematic, depending on the kind of dependence involved. The notion of self-causation was widely regarded as incoherent (e.g., see Arnauld’s objections to Descartes (1641; CSM II/148–50); for an exception, see Spinoza 1677; Id1), but self-grounding or self-explanation seemed less objectionable. Still, for present purposes, we can stipulate that metaphysical dependence is asymmetrical and irreflexive, in which case God is excluded from the scope of CD.

  6. 6.

    For examples from familiar bookends, see Aquinas (1947; q1, art 1, reply) and Leibniz (1697; PE 152 and 1710; G VI/439). For more on the early modern debate about the dependence of possibilia and possibilities on God, see Newlands 2013.

  7. 7.

    For even more Platonic-sounding versions, see Leibniz (1690(?); L 367) and (1710; T 51). Leibniz’s doctrine of creaturely composition grew out of his early work on the ontological argument, and it plays an important role in his account of the metaphysical origins of evil; for more, see Newlands (2014).

  8. 8.

    For more details and textual support, see Newlands (2013).

  9. 9.

    For but one of many passages, see Leibniz 1710; T 267–8.

  10. 10.

    This would be a kind of representational holism not unlike Spinoza’s holist doctrine about the mind-relativity of mental content (see Della Rocca 1996, pp. 44–67). An analogy from fiction might help: readers can grasp and even entertain a character’s fearful perspective while at the same time, perhaps by also being aware of how the story ends, prevent that representation of fear from becoming a fearful representation.

  11. 11.

    See, for examples, Spinoza 1677; Ip15s and Ip28. For an interesting passage in which Leibniz distinguishes an argument based on God’s perfection from an argument based on the PSR, even though both reach the same conclusion, see Leibniz 1716; LC 28.

  12. 12.

    I have argued elsewhere (Newlands 2013, Sect. 3.2) that Leibniz’s grounding of creaturely possibilities entirely in God’s ideas forces him to reject certain explanatory demands and admit that God’s intellect contains some primitive content, so it might be that Leibniz must already reject some versions of the PSR when applied to God.

  13. 13.

    Malebranche is even more explicit that the character of God’s ways of acting is meant to optimally reflect God’s own attributes (most notably, God’s simplicity). See Newlands (forthcoming) for more on Malebranche’s version, which differs from Leibniz mostly on an orthogonal issue concerning the relation between worlds and laws.

  14. 14.

    Translation slightly modified. For additional citations and discussion, see Newlands 2018, p. 34–36. Although I am focusing on the structural element here, there is also a generative component of this account: the simplest base generates the greatest variety. (Thanks to Kris McDaniel for emphasizing this point in conversation.).

  15. 15.

    The reason for thinking identity is the limit case of unity for Leibniz is his frequent insistence that substances are the only true unities, that is, that only individual substance is a unity per se. Hence, complete unity need not and, in per se unities, cannot involve more than one individual.

  16. 16.

    Leibniz sometimes treats perfection as a gradable type of monadic properties had by individuals; in this sense, each thing can have multiple perfections in varying degrees. Throughout the rest of this discussion, I will focus on Leibniz’s account of perfection as a single, tokened polyadic property of individuals and worlds. (For a text in which Leibniz moves back-and-forth quickly, see 1677; A 6.4.1354).

  17. 17.

    This is reminiscent of Spinoza’s claim that “the more being or reality each single thing has [unumquodque], the more attributes belong to it” (1677; Ip9).

  18. 18.

    For examples, see (1671; CP 3), (1677–78(?); A 6.4.1362), (1697; PE 150–1), and (1714; PE 210).

  19. 19.

    One interpretative reason this is worth emphasizing is that there are passages in which Leibniz claims that maximizing the quantity of reality or essence is God’s aim in creation (e.g., (1680(?); A 6.4.1442), (1687; PE 87), (1697; PE 150)), but those passages could be read as shorthand for this structural account, in which the quantity of qualities or states (“reality”) is measured against the quantity of individual bearers of those states (as the very next paragraph in 1697; PE 150 bears out).

  20. 20.

    He actually refers to “household managers,” but this seems like a fair extrapolation. For Leibniz’s clearest appeal to the ubiquity of this measure, see (1686; PE 38); see also (1671(?); A 6.1.484–5), (1677–78(?); A 6.4.1359) and (1697; PE 150–1).

  21. 21.

    For a more critical comparison, see Newlands (2017); for direct objections to Schaffer’s account, see Baron and Tallant (2018).

  22. 22.

    See also Leibniz (1677(?); A 6.4.1354), (1697; PE 150–1), and (1714; PE 210).

  23. 23.

    For examples from different periods, see Leibniz (1672; CP 29–31), (1686; PE 67–8), (1697; PE 152–3), (1697(?); MP 147), and (1710; T 258). A referee pointed out that Leibniz’s God might also be concerned with the amount of moral goodness and divine justice for rational creatures in possible worlds, but Leibniz stoutheartedly insists that those desiderata are satisfied insofar as God takes into account only their perceptions of metaphysical perfection: “It also follows that the world is morally most perfect, since moral perfection is in reality physical perfection with respect to minds” (1697; PE 152–3), and “an intelligent being’s pleasure [i.e., physical perfection] is simply the perception of beauty, order and perfection…the consequence of this is that in the universe, justice is also observed, for justice is simply order or perfection with respect to minds” (1697(?); MP 146–7).

  24. 24.

    There are difficult questions about the modal status and modal implications of DA, something Leibniz worried about a great deal. But the path to yet another form of Spinozism—necessitarianism—is an issue I will set aside here. (For my own take on it, see Newlands 2010).

  25. 25.

    For early versions of this idea, see Leibniz 1676; DSR 21–23 and 29. For another middle period version, see Leibniz 1687; PE 87.

  26. 26.

    Although Leibniz calls these states “perceptions,” it is now common to think that what we ordinarily call perceptions are essentially embodied forms of cognition. So I will stick with “representations,” which I take to be the sorts of states that disembodied mental substances could have (if such substances are metaphysically possible at all.) In the present context, a tu quoque with theists will suffice: whatever sort of mental states God has that have the right form and content to allow God to think about possible worlds prior to creation is the relevant kind of mental state for this argument..

  27. 27.

    For ease, I will drop the “or mind-like” qualification, as the relevant feature of minds that will do the work is their representational capacity, which Leibniz thinks mental substances can have without being rational minds.

  28. 28.

    Leibniz makes a similar slide in 1714; PE 207.

  29. 29.

    There is a different backdoor fix that would unhelpfully complicate the dialectic. Suppose we grant Leibniz an additional a posteriori premise derivable from introspection: God actually created finite minds (see 1714, PE 215). Then MA will be: Given that God in fact created minds with their representational states, God did not need to create anything else in order to achieve optimal harmony, and so, by DA, God didn’t, and hence idealism is true. But in this context, that’s unhelpful because it spots Leibniz a premise that, if the next section is correct, he is not entitled to (introspection be damned), namely that God has created finite substances at all.

  30. 30.

    As a referee pointed out, it is worth keeping in mind that Leibniz offers other, independent arguments for idealism that might not be susceptible to the same monistic pressures. My target is perfection-based arguments like MA, rather than, e.g., Leibniz’s argument from aggregates (1714, PE 213).

  31. 31.

    For examples, see Leibniz (1686; PE 47), (1698; L 493), (1714; PE 214 and 220), and (1716; LC 57). As a referee tactfully noted, one might be suspicious of the Leibnizian thesis that all varieties and aspects of representational character really supervene on the distribution of representational clarity and distinctness. For a helpful discussion that gives a good sense of how rich the Leibnizian resources might be here, see Jorgensen (2015).

  32. 32.

    Admittedly, Leibniz thinks each perceptual series in infinitely long, so it will be a while before the sequence begins to repeat. But I am really just working up to the monistic upshot here, so even if this worry entails that God would have a perfection-based reason to create a multiplicity of minds if God were to create any of them, I will argue shortly that God does not have a sufficient reason to create any finite minds in the first place.

  33. 33.

    Leibniz might be seen as reasoning ab effectu here, much as he often does when faced with objections to the bestness of our world. Perhaps we cannot see why LMW is not the best, but since we know that ours is not the lonely world, we know ab effectu that LMW is not the most perfect. There are reasons to be suspicious of this parallel, however. For one, the sorts of considerations that Leibniz (1710; T 135) thinks explain our inability to calculate the overall bestness of our world do not apply when calculating the relative metaphysical perfection of lonely and non-lonely worlds. For another—although this threatens to dissolve into familiar skeptical worries—in light of the argument above, exactly whence lies our (!) confidence that our world isn’t LMW? (I’ll leave it up to the reader to decide which of us is the real perceiver in that case; I know which way I’m voting).

  34. 34.

    This label is somewhat infelicitous. Contra “world,” Leibniz does not think that God is a member of any possible world, a point that by itself should give us pause when assimilating his modal views to a contemporary possible world framework. But that does not matter here, so long as Leibniz admits that it is metaphysically possible that God create nothing. Contra “lonely,” Christian monotheists like Leibniz can point to the rich inter-personal relations among the persons of the Trinity, so it is “lonely” only in the sense that it lacks any substances other than the sole divine substance.

  35. 35.

    Shockingly, Ariew and Garber add a footnote to the word “identity” in this passage: “This might be a slip of the pen for ‘regularity’.” Slip of the pen, indeed! A more apt editorial comment might have been: “Old habits die hard”.


References to Leibniz’s works are cited by page number and abbreviated as follows:

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I am especially grateful to Fatema Amijee for all of her hard work arranging and editing this exciting journal issue. I am also thankful to Fatema and Dai Heide for organizing an outstanding conference on the PSR at Simon Frasier University in 2018, at which Dai provided excellent commentary on an earlier version of this paper. I also thank participants of that PSR conference, as well as participants of the Center for Philosophy of Religion and early modern discussion groups at Notre Dame, for helpful discussion and pushback.

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Newlands, S. From theism to idealism to monism: a Leibnizian road not taken. Philos Stud (2020).

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  • Monism
  • Idealism
  • Leibniz
  • Perfection
  • Theism
  • Early modern