This was my study guide I put together for an examination I took on Spinoza’s substance monism in grad school.
Note: [1P*] refer to premises, [1A*] refer to axioms, and [1D*] refer to definitions.
The root idea behind the notion of substance in Spinoza [S] is what has properties or is a subject of predication. But it cannot be just anything serving this role; otherwise a great many things in the world would qualify which S doesn’t want to say. The notion as S uses it (and was defined by Descartes) includes items which are causally self-sufficient or indestructible. S tells us in [1D3] that substance is what is in itself, conceived through itself, and doesn’t require any other concept for its formation. In other words, substance is self-caused, self-sufficient, and has complete independence from all other things in its formation. A further point which follows from this def. comes from [1D1] where S defines self-cause as a thing whose essence requires existence or whose nature cannot be conceived except as existing. Why must existence be part of the essence of substance? Because substance is gonna be the substratum from which the universe exists and such can’t itself contingently exist.
Essence also appears in [1D4] where S tells us that an attribute is what the intellect perceives of a substance, as constituting its essence. There are ambiguities and different interpretive strategies by scholars concerning this def. but I think the best way to explain it is by saying that attributes are the basic ways in which the human intellect can, in their limited fashion, comprehend the nature or essence of substance; and humans have access to two attributes which are extension and thought. That said, let me throw out one more def. before moving on to S’s main argument.
[1D5] defines a mode as the affections (or predicates) of a substance…conceived through another. In other words, modes are all the particulars, finite things found in the universe, which are predicated on substance and understood through the attributes of extension and thought.
Main Argument for Spinoza’s Substance Monism
There are five main steps, as I see it, involved in Spinoza’s argument for substance monism, the first being the ‘no shared attribute’ thesis found in [1P5]. The premise, which says that “in nature there cannot be two or more substances of the same nature or attribute,” rests on two earlier premises: [1P4] which says that two or more distinct things are distinguished either by a difference in their attributes or a difference in their modes. This is Spinoza’s version of the identity of indiscernibles, which says that for A ≠ B means that A has or lacks some attribute or mode which B either has or doesn’t have, and [1P1] which states that substances are prior to their modes. The argument goes like this:
If A and B are distinct, they are distinct either in their attributes or their modes (1p4). Thus if A and B are distinct but share their attributes, they must have different modes. If A and B can be conceived as distinct through their modes, A and B can be conceived through their modes. But a substance cannot be conceived through its modes (1p1). So if A and B are distinct but share their attributes, they cannot be
conceived of as distinct. Thus their distinctness cannot be conceived. So if A and B are distinct they must differ in their attributes. Hence no two substances can share an attribute (1p5).
The second move comes at [1P7]: It pertains to the nature of a substance to exist. The argument for this premise comes from [1D1] and from [1P6C] which says that substance cannot be produced by anything else. [1P6C] comes as a result of [1P6] which states that one substance can’t produce another substance. What drives [1P6] is the [1P5] along with [1P2] which says that substances with different attributes have nothing in common with each other. If substances have different attributes and those attributes have nothing in common with each other, then they can’t play any sort of causal role with each other by [1P3]. And if substances can’t causally affect each other, then [1P6C] follows for substances and affections are all there are in nature. Thus, substance is self-caused and exists by its own nature.
The third move comes at [1P11]: God, or a substance consisting of infinite attributes, each of which expresses eternal and infinite essence, necessarily exists. The first thing to point out is minus the “necessarily exists” part, this is S’s def. of God found in [1D6]. Next, the “infinite attributes” clause is not merely definitional, there is an argument for substance being necessarily infinite found at [1P8]. The argument for that premise rests on [1P5], [1P7], and the def. of finite at [1D2]: a thing is finite if it can be limited by another of its own nature. Now, S runs to arguments for [1P11], a version of the ontological argument (which I shall pass over), and a more interesting causal argument which goes like this:
Everything must have a cause for both its existence and non-existence. This cause must either come from within it or from outside of it. Substance (God) exists according to its own nature and must do so. If something were to cause God to not exist, therefore, it would have to come from outside of God. But a substance that is separate from God would have nothing in common with God [1P2, 1P5] and could not cause God to not exist. Therefore, if God cannot cause his own non-existence, and nothing outside God can cause his non-existence, then God must necessarily exist.
The fourth step comes at [1P14]: Except God, no substance can be or be conceived. This is the decisive move for showing the monistic quality of S’s metaphysics. The argument for this premise rests on [1D6, 1P11, and 1P5] and runs like this:
God is an absolutely infinite being containing infinite attributes and who necessarily exists. If there were another substance which also existed, it would have to be explained through one of God’s attributes since God contains the infinite quantity of them. But two substances cannot be explained through the same attribute. Also, since it’s part of a substance’s nature to exist, for it to be or be conceived of would involve it being conceived through at least one attribute. Therefore no other substance but God can be or be conceived of.
The final step to this argument is at [1P15]: Whatever is, is in God, and nothing can be or be conceived without God. This argument stems from [1P14, 1D3, 1D5, and 1A1] and runs like this:
Except for God, there neither is, nor can be conceived, any substance that is in itself and conceived through itself. Modes, on the other hand, can neither be nor be conceived without substance. Only substances and modes exist. Therefore, everything is in God, and nothing can be conceived without God.
Here’s the five steps sans explanation:
- [1P5] In nature there cannot be two or more substances of the same nature or attribute.
- [1P7] It pertains to the nature of a substance to exist.
- [1P11] God, or a substance consisting of infinite attributes, each of which expresses eternal and infinite essence, necessarily exists.
- [1P14] Except God, no substance can be or be conceived.
- [1P15] Whatever is, is in God, and nothing can be or be conceived without God.