Spinoza on Substance & the PSR

Here I discuss some issues concerning the manner in which the PSR figures in Spinoza’s argument for substance monism in Ethics I. Special attention is paid to connections between Spinoza’s and Descartes’s views, as well as which, if any, version of the PSR Spinoza endorses.

1 Spinoza on the PSR & Intelligibility

Spinoza is often characterized as an arch-rationalist, insofar as he is credited with claiming that reality is fundamentally intelligible and that there are no brute (i.e. unexplained or unintelligible) truths or facts.1 Many have thus thought it plausible to read Spinoza as a “metaphysical or ”explanatory“ rationalist.

Explanatory Rationalism:
For every fact F, there is a sufficient explanation (or reason/ground) why F, rather than not F, is the case

This sort of explanatory rationalism is metaphysical, in the sense that it makes a claim about how reality is – namely such as for there to be an explanation of every fact. It is also broadly epistemological (or even conceptual), in the sense that it considers this relation between facts to be one that is understandable or rational.

To say, as in the second point, that explanation is both metaphysical and epistemic/conceptual, is to say that “explanation” picks out both a real relation between existences (call this the “grounding” relation) and the proper way of conceiving of those existences and their relation (Spinoza calls this “adequately conceiving” of something or having an “adequate idea” of it). To have an adequate conception of something is to understand that thing through its ground. For example, in his discussion of (real) definition Spinoza says,

If the thing be a created thing, the definition, as we have said, must include its proximate cause. For example, according to this rule a circle would have to be defined as follows: a figure described by any line of which one end is fixed and the other movable. This definition clearly includes the proximate cause.

The conception or definition of the thing must be such that all the properties of the thing, when regarded by itself and not in conjunction with other things, can be deduced from it, as can be seen in the case of this definition of a circle. For from it we clearly deduce that all the lines drawn from the centre to the circumference are equal.2

The importance of the definition is that it makes transparent the relation of consequent to ground, or of effect to cause. So the understanding the definiens gives one an understanding of way in which the existence of the definiendum follows from the existence of the definiens, which in the case of the circle, above, is the “inscribing” of a line that meets the stated conditions. So an adequate idea of a thing will include its cause, which explains why that thing has the fundamental features (i.e. the “essence”) that it does. This essence in turn explains all of the other features that the thing can have.

2 Statements of the PSR

We’ve seen that Spinoza endorses a form of explanatory rationalism, in the sense that he contends that every adequate idea of a thing involves possession of a real definition of that thing, and real definitions include the efficient or proximate cause of the thing’s existence. So every adequate idea is an idea of the essence of a thing and of the cause of its existence. But in what sense, if any, does this amount to an endorsement of the PSR?

Since there are many different ways to formulate “the” PSR, we must look to see whether in the Ethics Spinoza gives some indication of which version(s) he accepts. The first three axioms seem to indicate claims concerning the intelligibility of all things.

E1a1: Whatever is, is either in itself or in another. E1a2: That which cannot be conceived through another thing must be conceived through itself. E1a3: From a given determinate cause there necessarily follows an effect; on the other hand, if there be no determinate cause it is impossible that an effect should follow.

The first two axioms mirror each other. The first makes a metaphysical claim, the second a conceptual or epistemic claim. But they have the same structure, that what is or is conceived, is so either through itself or through another. In both cases we see a commitment to (on the one hand) the PSR_ontic and (on the other) the PSR_conceptual. Spinoza thus takes as axiomatic that nothing is groundless in its existence or in its conception. Spinoza makes further statements indicating his commitment to the PSR.

E1p8s2: there must be, for each existing thing, a certain cause on account of which it exists. E1p8s2: …[I]f a fixed number of individuals exist in Nature, there must necessarily be a cause why those individuals and not more or fewer, exist. E1p11d2: For every thing a cause or reason must be assigned either for its existence or for its non-existence.

The first relies on the PSR_ontic. The second is a straightforward statement of the PSR_ontic. What is notable about the statement in the latter is that it applies not only to what exists, but also to what does not exist. This means that not only does everything that exists have a ground but also that non-existence stands equally in need of explanation. Why would Spinoza think this? Does this doctrine commit him to an ontology of non-existing beings?

We can get a clue to Spinoza’s thinking here by looking at a further “alternative” argument he provides for God’s existence. He says,

E1p11d: To be able not to exist is to lack power [impotencia], and conversely, to be able to exist is to have power [potencia] (as is known through itself). So, if what now necessarily exists are only finite beings, then finite beings are more powerful than an absolutely infinite Being. But this, as is known through itself, is absurd. So, either nothing exists or an absolutely infinite Being also exists. But we exist, either in ourselves, or in something else, which necessarily exists (see Al and P7). Therefore an absolutely infinite Being-that is (by D6), God-necessarily exists, q.e.d.

Here we see Spinoza equate existence with a possession of power and non-existence with its lack. He also identifies God’s essence with power (E1p34) and power as flowing from the “reality” or (degree of) being of a thing.

E1p11d: since being able to exist is power, it follows that the more reality belongs to the nature of a thing, the more powers it has, of itself, to exist.

Similarly, Spinoza equates power, reality, and perfection.

E2d4: By reality and perfection I understand the same thing. E4Pref (II/208-9): when I say that someone passes from a lesser to a greater perfection, and the opposite, I do not understand that he is changed from one essence, or form, to another. … Rather, we conceive that his power of acting, insofar as it is understood through his nature, is increased or diminished. … by perfection in general I shall, as I have said, understand reality, that is, the essence of each thing insofar as it exists and produces an effect, having no regard to its duration.

God is, on Spinoza’s conception, the ens realissimum, i.e., the “most real” being, where “most real” is understood as possessing infinite perfection or reality, which entails infinite causal power. In this way, Spinoza’s understanding of God is rather traditional. Spinoza is effectively saying that God possesses infinite being. As he puts it in a letter from 1666:

since the nature of God does not consist in a definite kind of being, but in a Being [esse] which is absolutely unlimited, his nature also requires everything which expresses being perfectly, since otherwise his nature would be limited and deficient. (IV/185 in (Spinoza 2016, 30))

Since God is being, wholly unlimited and not yet determinate, anything that exists will be anything that follows from God’s nature, and similarly anything that doesn’t exist is anything that doesn’t follow from God’s nature. In this sense there is a ground both of what exists and of what does not.

Looking back at these passages then, we can see that the basic form that the PSR takes for Spinoza is not one concerning facts, but rather concerning existence. It is the PSR_ontic. This does not mean he rejects other forms of the PSR (e.g. the epistemic, alethic, explanatory, or state of affairs versions). Rather, he sees these other forms as derivative from the ontic version, because he sees all these as ways of articulating aspects of the way determinate being flows from the nature of being as such (i.e. of God or Nature).

One important question here then is how to understand the notion of “flowing from” or “following from” here. We saw above that Spinoza sees this flowing from as causal, and in giving the (real) definition of thing as enumerating the cause through which that thing as the thing that it is comes to be. So the definition of a circle includes appeal to its cause, the act of delineating a space with one fixed point (the center) and another that moves equidistant from this point. That constructive act is sufficient for a circle being what it is (for the circle’s nature or essence). Other properties of the circle can then be derived from the existing circle (and the facts that supervene on its existence). So, given that everything is caused and conceived through itself or through another, in the case of the circle we see that the “other” here is the act of geometric construction or delimiting in space.

It is important for Spinoza’s project that there is a single unitary sense in which one thing follows or flows from another. For example, he says,

E1p17s1: from God’s supreme power, or infinite nature, infinitely many things in infinitely many modes, that is, all things, have necessarily flowed, or always follow, by the same necessity and in the same way as from the nature of a triangle it follows, from eternity and to eternity, that its three angles are equal to two right angles.

So the “cause” or “reason” to which Spinoza appeals in the case of the circle is the same as that in the case of a triangle (and in the case of each of the figures’ further geometric properties), and similarly is so in the case of God. Spinoza thus wholly agrees with Descartes in thinking that if we ask why some existing is, we can ask that of anything, including God. In light of this I want to look more closely at Spinoza’s discussion of the explanation or ground of God’s existence and how this relates to the sense in which the first two axioms of E1 state that every is and is conceived either through itself or another.

3 God’s Necessary Existence

In E1P11, Spinoza aims to demonstrate the existence of God as a being consisting of infinite attributes. There are many issues surrounding this proof and its overall place in the argument of book one.3 The demonstration proceeds by reductio, arguing that the conception of a being with infinite attributes would be contradicted by positing that its essence did not contain existence.4 This seems like a straightforward version of the ontological argument. But Spinoza expands on this short demonstration, saying,

For each thing there must be assigned a cause, or reason, both for its existence and for its nonexistence. For example, if a triangle exists, there must be a reason or cause why it exists; but if it does not exist, there must also be a reason or cause which prevents it from existing, or which takes its existence away.

But this reason, or cause, must either be contained in the nature of the thing, or be outside it. For example, the very nature of a square circle indicates the reason why it does not exist, namely, because it involves a contradiction. On the other hand, the reason why a substance exists also follows from its nature alone, because it involves existence (see P7). But the reason why a circle or triangle exists, or why it does not exist, does not follow from the nature of these things, but from the order of the whole of corporeal Nature. For from this [order] it must follow either that the triangle necessarily exists now or that it is impossible for it to exist now. These things are evident through themselves; from them it follows that a thing necessarily exists if there is no reason or cause which prevents it from existing. Therefore, if there can be no reason or cause which prevents God from existing, or which takes his existence away, it must certainly be inferred that he necessarily exists.

The basic structure here is that of asserting a very strong version of PSR_ontic and using it argue through cases. Using “ground” as a shorthand for the cause or reason (causa seu ratio):

  1. There must be a ground for the existence or non-existence of a being (i.e. a substance or mode).
  2. The ground for the existence of a substance is part of its nature.
  3. ∴ The only ground for the non-existence of a substance would be something external to it (to its nature).
  4. If there is no ground preventing God’s (as a substance) existence, then God necessarily exists.

In the subsequent paragraph Spinoza proceeds to prove the antecedent of the conditional in (4). From that he then concludes that God necessarily exists.

4 God as (Self-)Caused

I want to conclude by looking at the sense in which Spinoza thinks God is self-caused. Spinoza broadly agrees with Descartes when the latter says,

Concerning every existing thing it is possible to ask what is the cause of its existence. This question may even be asked concerning God, not because he needs any cause in order to exist, but because the immensity of his nature is the cause or reason why he needs no [other] cause in order to exist. (7:164-5)

Descartes thus holds that God causes itself to exist by virtue of its own perfection, power, or immensity. Similarly Spinoza holds that “an absolutely infinite Being, or God, has, of himself, an absolutely infinite power of existing. For that reason, he exists absolutely” (E1p11s). Spinoza also identifies God’s essence with its power

E1p34: from the necessity alone of God’s essence it follows that God is the cause of himself (by pll) and (by p16 and p16c) of all things. Therefore, God’s power, by which he and all things are and act, is his essence itself

But we might wonder here whether we should take the notion of “causa sui” (self-cause) as a kind of efficient causal claim – that God is the cause of its own existence in a manner analogous to how, e.g., smelting ore is the cause of iron.

Consider the textual evidence.5

First, in E1p6c, Spinoza proves that “a substance cannot be produced by anything else [substantiam ab alio produci non posse]”. The terminology of ’producere’ here indicates that efficient causation is what is at issue. Moreover, if it weren’t efficient causation, but causation in some more general sense to which Spinoza were appealing the subsequent argument of E1p7d would be invalid. For it would leave open the possibility that while a substance cannot be produced (i.e. efficiently caused) by anything else, it could still be caused in some other sense by external factors.

Second, in E1p16, Spinoza contends that “God is the efficient cause of all things [omnium rerum] which can fall under an infinite intellect”. But God is also a thing (res), and God knows itself via its intellect (E2p3d and E2p4). So God must also be the efficient cause of itself.

Third, as discussed above, Spinoza claims that real definitions include the efficient cause of the definiendum’s existence. But nothing external to God can cause its existence. So God must be the efficient cause of itself.

Fourth, in a letter (Ep. 34) from 1666, Spinoza describes God as existing in virtue of its essence, but importantly characterizes existence‐by‐virtue‐of‐mere‐essence as “being produced by the force of its own nature [suae naturae vi produci]” (IV/180/21). The language of production here would seem to indicate that it is efficient causation that Spinoza has in mind.

Fifth, Spinoza holds in E1p25 that God is the efficient cause of the essences of things (rerum). If we take the scope of “things” here to be unrestricted, then God is the efficient cause of its own essence. Moreover, if God were not such a cause of its essence, God could be conceived of without God, and through another, which would contradict Spinoza’s E1p15, “Whatever is, is in God, and nothing can be or be conceived without God.”

There is a caveat here. Why doesn’t E1p17s2 pose a problem for the above? Spinoza says that

what is caused differs from its cause precisely in what it has from the cause …

the thing that is the cause both of the essence and of the existence of some effect, must differ from such an effect, both as to its essence and as to its existence

But the key issue here is the sense in which cause and effect are not numerically identical. Insofar as they are not there will be a differential between cause and effect in terms of reality or power. But since God is numerically identical to itself, there is no such difference in power or reality.

In the end, we have to determine whether it seems coherent to think of a thing being the efficient or productive cause of itself, rather than merely possessing the feature of necessary existence. For example, suppose we think the causal relation must have the following three features:

  1. Irreflexivity: if r causes s, then r ≠ s. (Alternatively: nothing can cause itself.)

  2. Asymmetry: if r is causes s, then s does not cause r.

  3. Transitivity: if r is a cause for s, and s is a cause for t, then r is a cause for t.

So does Spinoza accept that the causal relation, while asymmetric and transitive, is nevertheless at least possibly reflexive? It seems so. If that is the case then Spinoza differs from many contemporary philosophers of “ground” who hold that a ground must have all three of the above features.


Bennett, Jonathan Francis. 1984. A Study of Spinoza’s Ethics. Indianapolis: Hackett.
Curley, Edwin. 1988. Behind the Geometrical Method: A Reading of Spinoza’s Ethics. Princeton University Press.
Della Rocca, Michael. 2003. “A Rationalist Manifesto: Spinoza and the Principle of Sufficient Reason.” Modern Philosophy 31 (1/2): 75–93. doi:10.2307/43154409.
———. 2008. Spinoza. London: Routledge.
Garrett, Don. 1979. “Spinoza’s ``Ontological’’ Argument.” The Philosophical Review 88 (2): 198. doi:10.2307/2184506.
Hübner, Karolina. 2015. “Spinoza’s Parallelism Doctrine and Metaphysical Sympathy.” In Sympathy: A History, edited by Eric Schliesser, 146–70. Oxford: Oxford University Press.
Hübner, Karolina, and Róbert Mátyási. 2022. “Spinoza on Expression and Grounds of Intelligibility.” The Philosophical Quarterly 72 (3): 628–51. doi:10.1093/pq/pqab056.
Lin, Martin. 2007. “Spinoza’s Arguments for the Existence of God.” Philosophy and Phenomenological Research 75 (2): 269–97. doi:10.1111/j.1933-1592.2007.00076.x.
———. 2017. “The Principle of Sufficient Reason in Spinoza.” In The Oxford Handbook of Spinoza, edited by Michael Della Rocca, 133–54. Oxford: Oxford University Press. http://books.google.com/books?id=OWIwDwAAQBAJ&hl=&source=gbs_api.
———. 2019. Being and Reason. Oxford: Oxford University Press.
Melamed, Yitzhak Y. 2021. “Spinoza on Causa Sui.” In A Companion to Spinoza, edited by Yitzhak Y. Melamed, 116–25. Hoboken, NJ: John Wiley & Sons.
Smith, A D. 2012. “Spinoza, Gueroult, and Substance.” Philosophy and Phenomenological Research, no.
Spinoza, Benedictus de. 1994. A Spinoza Reader: The Ethics and Other Works. Princeton, N.J: Princeton University Press.
———. 2016. The Collected Works of Spinoza. Princeton, N.J.: Princeton University Press.

  1. For a recent ambitious version of this sort of reading of Spinoza see (Della Rocca 2008); see also (Della Rocca 2003; Hübner 2015; Lin 2017, 2019; Hübner and Mátyási 2022). ↩︎

  2. See Spinoza, Treatise on the Emendation of the Intellect, §96 in (Spinoza 1994, 52). ↩︎

  3. See, e.g., (Garrett 1979; Bennett 1984; Curley 1988; chapt. Della Rocca 2008, 2; Smith 2012; chapt. Lin 2019, 2). ↩︎

  4. See, e.g., (Garrett 1979; Lin 2007). ↩︎

  5. Here I follow (Melamed 2021). ↩︎