Is The Fundamental Level of Reality Divided into Mind and Body? Or Are Mind and Body Two Aspects of an Even More Fundamental Reality?
The answer to this question is the key distinction between Descartes and Spinoza. Lets unpack the two positions: In the Dualist view (Descartes) anything that exists is either an extended substance (Body) or a thinking substance (Mind). There is nothing more fundamental than these two types of substance; that is to say Mind and Body are not properties of some more fundamental substance. All properties either inhere in the substances of Mind or Body.
So how do we know there isn’t a more fundamental level of existence? The reason is that these two categories are conceptually distinct: if something is a body then we can identify it as such without appeal to anything beyond the properties of Body, the same is true of Mind. For example, consider the table in front of you: every single property you can attribute to the table (shape, extension, texture, weight, etc…) is a property of Body. We do not (and indeed cannot) invoke any properties of Mind to identify the table as being a body. In another case consider how you would identify your own mind: any property that you would use to identify your mind as your own mind (thought, imagination, feelings, etc…) is a property of Mind and not of Body (body’s don’t think). Because of this feature of “self-conception”, substances are conceptually distinct from each other–they are conceptually walled off from each other. To repeat: to identify a substance as a substance I should not need to refer to properties other than those properties which pertain to that particular substance.
So why does Descartes think that all existing things are made up of either Mind or Body? Because these notions are conceptually distinct/walled off from each other. But there is an important assumption here that Descartes makes: that a substance can have only one attribute (for Mind it is thought and for Body it is extension). Lets ignore for a moment that humans–by Descartes own admission–seem to possess both and ask if this is a good assumption. This is the angle from which Spinoza attacks Descartes.
Spinoza vs Descartes
Spinoza is an uber-rationalist which means that for every fact in the world, there must be an explanation, otherwise we cannot claim to know if a fact is true. This principle of Spinoza’s rationalism is called “the Principle of Sufficient Reason” (PSR). But the demand for explanations doesn’t end there; Spinoza also applies the PSR to facts about non-existence. For instance, if something doesn‘t exist, we need to provide a sufficient reason to explain why it can’t exist.
So lets get back to Descartes assertion that a substance can only have one attribute. Spinoza rejects Descartes assumption because he hasn’t given sufficient reason for which we should believe this. Spinoza argues that we have no reason to suppose that a substance couldn’t possess 2 or more attributes. Just because thought and extension are conceptually distinct notions doesn’t mean that a thing could not possess both. Another way to look at is, just because two things are conceptually different doesn’t necessarily imply that they constitute two different substances.
This argument is partly how Spinoza advances his own position of Monism. So, what’s Monism? In Spinoza’s case it is the idea that Mind and Body are just two of many possible aspects of the one and only substance. Since there is no sufficient reason to show that a substance can’t have more than one attribute, Monism the logical conclusion.
Well, that’s half the argument. The other half concerns why Monism must be the case, because simply showing that something is a possibility isn’t grounds for its truth. But I will leave that argument for next time. For now, I’ll end with a few random comments on what Monism is for Spinoza:
The one substance in which all things inhere is God. But this is not some mystical and/or anthropomorphized god who (magically) lives outside of time and space and is not subject to the laws of the natural world. God, for Spinoza, is nature. God is not some entity that partakes in Nature either. The two are one and the same. Nature is the substance of which all things are properties, or modes. Nature has an absolute infinite number of attributes of which Mind and Body are but two. Because Spinoza’s views were basically philosophical naturalism, Spinoza didn’t publish his work during his lifetime because he knew he’d probably end up dying the death for his views. Instead he had his friends publish his works after his death.