Substance monism / Deus sive Natura: is there one and only one substance, of which all finite things are modes, or do the definitions admit a plurality of substances and finite created things in their own right?

Baruch Spinoza, answered from the texts and cited to the page.

The position in brief

Substance is what is in itself and conceived through itself (E1d3); mode is what is in another and conceived through another (E1d5); attribute is what the intellect perceives of substance as constituting its essence (E1d4).1 The first eleven propositions of Part I, given the definitions, the axioms, and the unrestricted Principle of Sufficient Reason according to which every existing or non-existing thing must have a cause or reason, demonstrate that there is one and only one substance — that this one substance is absolutely infinite, consisting of infinite attributes — and that all finite things are modes of this one substance, expressed in one or another of its attributes.23

To this one substance I give the name God or Nature, Deus sive Natura. The God of the Ethics is not the personal anthropomorphic deity of Abrahamic religion; God is the immanent cause of all things (E1p18), the natura naturans of which the modal world is the natura naturata, a being whose essence involves existence (E1p11) and which is causa sui — its own cause.4

Modes are real, not illusory; their reality is the actuality of God-as-modified, not the existence of a separate ontological tier of created substances over against the divine substance. The world is in God, and God is the immanent cause of the world; this is not pantheism in any sense in which pantheism means the identification of God with the totality of natural objects, and it is not acosmism in any sense in which acosmism means the dissolution of finite reality into mere appearance.

Sources

  1. Q.E.D. PROP. IX. The more reality or being a thing has, the greater the number of its attributes (Def. iv.). PROP. X. Each particular attribute of the one substance must be conceived through itself. Proof.--An attribute is that which the intellect perceives of substance, as constituting its essence (Def. iv.), and, therefore, must be conceived through itself (Def. iii.). Q.E.D.
    Ethics
  2. Proof.--The proof of this proposition is similar to that of the preceding one. PROP. XXIII. Every mode, which exists both necessarily and as infinite, must necessarily follow either from the absolute nature of some attribute of God, or from an attribute modified by a modification which exists necessarily, and as infinite. Proof.--A mode exists in something else, through which it must be conceived (Def.
    Ethics
  3. Proof.--This proposition is evident from Part i., Ax. iv. For the idea of everything that is caused depends on a knowledge of the cause, whereof it is an effect.
    Ethics
  4. Produced by Tom Sharpe. HTML version by Al Haines. The Ethics (Ethica Ordine Geometrico Demonstrata) by Benedict de Spinoza Translated from the Latin by R. H. M. Elwes PART I. CONCERNING GOD. DEFINITIONS. I. By that which is self--caused, I mean that of which the essence involves existence, or that of which the nature is only conceivable as existent. II.
    Ethics

Where the argument is made

  • Ethics Part I — especially the definitions (E1d1-d8), axioms (E1a1-a7), and propositions E1p1-p15 (the demonstration of substance monism)
  • E1p18 (God as immanent cause)
  • E1p29 (necessitarianism following from monism)
  • the Short Treatise Part I (the early statement of the position)
  • Letter 50 to Jelles (on whether God can properly be called 'one')

How the argument was received

The metaphysical foundation of Spinoza's system and the single most-discussed position in early-modern philosophy. Pierre Bayle's seventeenth-century charge that Spinoza's monism is pantheism-as-atheism set the polemical line of reception that ran through the eighteenth-century pantheism controversies. Hegel made Spinoza the necessary first step of speculative philosophy ("to be a philosopher one must first be a Spinozist") but read the monism as acosmist — finite things dissolve into the One; the Hegelian charge has dominated continental reception. The Anglophone analytical recovery has run through Curley's analytic systematic reading (Spinoza's Metaphysics 1969; Behind the Geometrical Method 1988) and Bennett's analytical critique (A Study of Spinoza's Ethics 1984) — both of which read the monism as a serious metaphysical position to be reconstructed from the definitions. Della Rocca's Spinoza (2008) and The Parmenidean Ascent (2020) defend the monism as the most rigorous expression of unrestricted PSR-rationalism. Melamed's Spinoza's Metaphysics: Substance and Thought (2013) defends the monism against analytical-tradition attempts to domesticate it into modal-property frameworks.