Substance Monism
- Posted by Andrew Bailey on Thursday, August 09, 2007 at 3:04 PM
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The history of philosophy of littered with monists. Parmenides was a monist about our most general sortal terms (`thing', `object'); the later Plato was (probably) a monist about Form. Aquinas was (arguably) a monist about human Soul. With these luminaries stands Spinoza, a substance monist.
I shall here articulate Spinoza’s central argument for substance monism as clearly as I can. I shall begin with a few definitions, present the argument as a whole, and then give Spinoza’s sub-arguments for the controversial premises.
Definitions
x causes y iff the concept of x includes the concept of y. For Spinoza, the notions of explanation and causation can be completely understood by means of a primitive inclusion relation holding between concepts.
x is a substance iff there isn’t any y (x≠y) such that the concept of y includes the concept of x. Spinoza thinks that the notion of dependence is completely capture by that of causation. So his notion of substance (against Aristotle’s) follows that offered by Descartes; a substance is something that’s ontologically autonomous or free of dependence on distinct things.
Consequence: x is a substance iff there isn’t any y (x≠y) such that y causes x.
The Master Argument
Substance monism is the thesis that there is one and only one substance. Following is his most widely-discussed argument for this thesis.
1. No two substances can share an attribute.
2. Every substance has an attribute.
3. There is a substance S, infinite in attribute (having all and infinitely many attributes).
4. Thus, if there were a substance T (S≠T), T would have an attribute not had by S (from 1, 2, 3).
5. But 4 is absurd.
6. So there is one and only one substance.
The First Argument for Premise (1)
Spinoza offers two lines of reasoning in support of premise (1). First, he expands his notion of substance to include notions I think best are captured by part/whole talk. His expanded notion of substance is captured, I think, by something like:
x is a substance iff there isn’t any y (x≠y) such that some part of the concept of y includes some part of the concept of x.
He then argues as follows: suppose for reductio that x and y are distinct substances sharing an attribute. From this, it follows that a part of the concept of x is included in some part of the concept of a distinct y. But if this is the case, then x isn’t a substance (for one, it has a part caused by or dependent on some part of y), contrary to assumption. Reductio complete.
The Second Argument for Premise (1)
The second argument for premise (1) looks something like this:
Suppose x and y are distinct substances sharing an attribute. By the Logical Principle of Sufficient Reason, it follows that there’s a reason why x and y are distinct substances. That is to say, there’s an individuator--something in virtue of which x and y are distinct.
There are two possible candidates of individuation. The first is mode. But modes are posterior to substances (they depend on their substances, not the other way around); and surely the thing individuating substances is prior to them. So modes don’t individuate substances. The second candidate is attribute. But by hypothesis, x and y overlap on an attribute. So it cannot be attribute that individuates x and y as substances. Otherwise x and y would be the same in attribute but distinct in substance.
It’s obvious that there’s a problem here (as Leibinz will later point out). The overlap of x and y on one attribute doesn’t entail the overlapping of x and y on all attributes. For all we know, x might have attributes {a, b, c}, while y has attributes {c, d, e}. In this case, attribute difference might still do the work of individuating x and y despite their overlap on one attribute.
The Argument for Premise (3)
Spinoza advances a novel ontological argument in support of premise (3). It goes something like this:
The Principle of Sufficient Reason says that for anything that exists or anything that doesn’t exist, that thing has a cause of existence or a cause of non-existence. So if God didn’t exist, then there’s a cause of his non-existence. This cause must be either in God or in something else. Not the former, since God’s being the cause of his own non-existence would be an imperfection, contrary to our definition of God as the being of infinite attribute. So if God didn’t exist, he has a cause of his non-existence in something else. That is to say, there’s a concept properly including God’s concept which is cause of God’s non-existence. Now by definition, God’s concept includes all other concepts (infinitely many of them, in fact). So there isn’t any concept which properly includes God’s existence. So there can be no reason for God not to exist. So God does exist. That is to say, a substance of infinite attribute exists.
It's worth noting that Spinoza's formulation of the Causal Principle of Sufficient Reason is equivalent to his formulation of the Logical Principle of Sufficient Reason (Leibniz' formulations of the two principles are not, I take it, equivalent). Most importantly, Spinoza's formulation demands a sufficient reason, not just for anything that exists, but also for things that don't!
Consequences
Spinoza is left with a puzzle. For it appears that there are things distinct from God, and yet he’s found a proof that God is the only substance. What are we to make of these things (that is, everything that isn’t identical to God)?
His answer: everything is either a substance or in a substance. By the Master Argument, nothing other than God is a substance. So everything other than God is nonetheless in God. Our concepts are all properly included in the concept of God.
