Hume’s chapter concerns the theory that the mind is immaterial. His answer is that there are decisive arguments against both materialist and immaterialist theories of the mind.
To be more specific, Hume has four arguments in this chapter.
An argument for abandoning substance, whether material or immaterial (Hume [1739] 2019, 563–64).
An argument about the possibility of so-called “local conjunction,” which we know as the problem of the interaction between material and immaterial substances (Hume [1739] 2019, 564R–567L).
An argument based on assumptions about the nature of substance (Hume [1739] 2019, 567L–569R).
An argument about causation (Hume [1739] 2019, 569R–571L).
I will give you a quick rundown of each of these arguments. The first argument stands on its own. The second and third arguments seek to show that arguments made against materialist theories of the mind apply to immaterialist theories as well. And the fourth argument is meant to rebut an objection to materialist theories.
There are two reasons why substances should go, according to Hume.
First, we do not have an idea of what they are. Hume phrases this in terms of his overarching theory that all ideas are derived from what he calls “impressions,” where impressions are sensory experiences. Since no one ever directly experiences a substance, no one has an idea of it. He probably could have made the same argument without the impressions-ideas theory. Everyone concedes that substances are inferred and, ultimately, unknowable.
The second argument is more interesting. If substance is understood as “something which may exist by itself,” as Descartes and Spinoza have it, then everything is a substance, according to Hume. That is because, as he sees it, every sensory quality can be imagined to exist on its own, apart from every other.
Now, you might say that sounds a bit outlandish. Can color exist on its own, without being the color of something else? Well, go to the Skyspace behind Edmunds Hall] at dawn or dusk. You tell me what the color you see in the middle is a color of.
Hume’s argument does not depend on that, but I think it’s a nice illustration of the idea. Plus the Skyspace is very cool.
Here is an argument made against materialist theories of the mind, like Hobbes’s. Thoughts and perceptions are indivisible and non-extended while matter is divisible and extended. So a thought cannot be part of a material body like a brain. Where would it go? On the right? In the middle? There cannot be a local conjunction of a thought and a material body (Hume [1739] 2019, 564).
This launches Hume on a long digression about how local conjunction works. Among other things, he claims that some things, like passions and other emotions (“sentiments”) and all sensory perceptions other than sight and feeling do not have any place in space. They exist “no where” (Hume [1739] 2019, 565L).
Eventually, Hume wheels around to the point, namely, that the argument deployed against the materialist theory of the mind can also be made against immaterialist theories of the mind. Some thoughts are extended. So how could they be conjoined to an indivisible, non-extended, immaterial mind (Hume [1739] 2019, 566R–67L)?
Vocabulary note. A “freethinker,” according to the Oxford English Dictionary, is “a person who professes to or is known for independence of thought, especially one who withholds assent to widely held beliefs or ideas; specifically a person who refuses to submit his or her reason to the control of authority in matters of religious belief.” In this context, freethinkers would be inclined to the materialist view while the immaterialist view is more aligned with religious thinkers.
This is very similar to a point that Evan was making last week about Berkeley. Let’s see if he likes the way Hume did it.
The argument is long and twisty, but in a nutshell, it is an attempt to say that every criticism made against Spinoza’s monism also applies to immaterialist theories of the mind.
Spinoza says that the universe of objects are only modifications of a simple, indivisible substance. The theologians say the same thing about the universe of perceptions and ideas. But the two have the same things: sun, moon, stars, the earth, seas, plants, animals, men, ships, houses, etc. (Hume [1739] 2019, 568L). The ideas of those things be a modification of the simple, indivisible mental substance. And that, according to Hume, gives rise to the same objections that were made against Spinoza’s “hideous hypothesis” (Hume [1739] 2019, 567L).
Note that Hume presents the argument on p. 568, in the left column. Then he restates it, going over each point in greater detail on the right column and the left column on p. 569.
You can skip the stuff about action on p. 569. That is an idea we are not going to concern ourselves with.
Here is an objection to materialist theories: the movement of matter cannot cause a psychological event, like a thought or sensation.
Hume uses his theory of causation to refute this objection. That theory holds that we never understand why any cause makes its effect necessarily happen. The most we can say about the relationship between cause and effect is that the things we call causes are “constantly conjoined” with their effects. (We will see this theory next week.)
Since there is no restriction on the kinds of things that might be constantly conjoined, there is no reason to think one kind of thing, like the movement of matter, cannot cause another kind of thing, like a thought.
Have a look at this passage. What is the materialist theory that is under discussion here?
It is absurd to imagine that motion in a circle, for instance, should be nothing but merely motion in a circle; while motion in another direction, as in an ellipse, should also be a passion or moral reflection: that the shocking of two globular particles should become a sensation of pain, and that the meeting of two triangular ones should afford a pleasure. Now as these different shocks and variations and mixtures are the only changes of which matter is susceptible, and as these never afford us any idea of thought or perception, it is concluded to be impossible that thought can ever be caused by matter. (Hume [1739] 2019, 569–70)
A materialist theory should hold that thoughts are motions of matter. I think that is suggested by the examples at the top. At the bottom, Hume is saying that the theory is that thoughts are caused by motions of matter, which seems to be to be rather different.
What is the relationship between the immateriality of the soul and its immortality? See the last paragraph on p. 571R.