Taxonomizing Answers to the Mind-Body Problem
A helpful framework that uses the least pithy names you can imagine
The mind-body problem is the problem of understanding how mind and matter are related. In this post, I want to propose a way of taxonomizing all possible answers to it. Here’s my suggestion: Each answer to the mind-body problem is the conjunction of a categorical view, a foundational view, and a structural view. Categorical views make a claim about the types of substances and properties that exist. Foundational views make a claim about the types of substances and properties that are fundamental. Structural views make claims about the relations that substances and properties bear to each other. My plan is as follows. In §1, I’ll map out the categorical views that I take to exhaust logical space. In §2, I’ll map out the foundational views. Finally, in §3, I’ll discuss the options available for relational views and address some counterintuitive consequences of my framework.
1. Categorical Views
I submit that there are sixty-four categorical views. Each one is the conjunction of a categorical substance thesis, which makes a claim about the sorts of substances that exist, and a categorical property thesis, which makes a claim about the sorts of properties that exist. There are eight substance theses and eight property theses one might hold, all of which are compatible with each other in principle.
Let’s examine the categorical substance theses first. A good way to understand them is to take the categorical substance test.
The Categorical Substance Test
Which sorts of substances exist? You can pick zero, one, two, or all three options.
Physical substances
Mental substances
Neutral substances (which are neither mental nor physical)
How many did you choose? If you chose zero, you’re a categorical substance eliminativist.
If you chose one, you’re a categorical substance monist. There are three classes of categorical substance monists. If you think there are only physical substances, you’re a categorical substance physicalist. If you think there are only mental substances, you’re a categorical substance idealist. If you think there are only neutral substances, you’re a categorical substance neutralist.
If you chose two, you’re a categorical substance dualist. There are three classes of categorical substance dualists as well. If you think that physical and mental substances both exist, but not neutral substances, you’re a categorical mental-physical substance dualist. If you think that physical and neutral substances both exist, but not mental substances, you’re a categorical physical-neutral substance dualist. If you think that mental and neutral substances both exist, you’re a categorical mental-neutral substance dualist.
Finally, if you chose all three from the list, you’re a categorical substance pluralist.
Now, let’s consider categorical property theses. Correspondingly, a good way to understand these is to take the categorical property test:
The Categorical Property Test
Which sorts of properties exist? You can pick zero, one, two, or all three options.
Physical properties
Mental properties
Neutral properties (which are neither mental nor physical)
How many did you choose? If you chose zero, you’re a categorical property eliminativist.
If you chose one, you’re a categorical property monist. There are three classes of categorical property monists. If you think there are only mental properties, you’re a categorical property physicalist. If you think there are only physical properties, you’re a categorical property idealist. If you think there are only neutral properties, you’re a categorical property neutralist.
If you chose two, you’re a categorical property dualist. There are three classes of categorical property dualists as well. If you think that physical and mental properties both exist, but not neutral properties, you’re a categorical mental-physical property dualist. If you think that physical and neutral properties both exist, but not mental properties, you’re a categorical physical-neutral property dualist. If you think that mental and neutral properties both exist, you’re a categorical mental-neutral property dualist.
Finally, if you chose all three from the list, you’re a categorical property pluralist.
In sum, there are eight categorical substance theses:
Categorical substance eliminativism
Categorical substance physicalism
Categorical substance idealism
Categorical substance neutralism
Categorical mental-physical substance dualism
Categorical physical-neutral substance dualism
Categorical mental-neutral substance dualism
Categorical substance pluralism.
And eight categorical property theses, too:
Categorical property eliminativism
Categorical property physicalism
Categorical property idealism
Categorical property neutralism
Categorical mental-physical property dualism
Categorical physical-neutral property dualism
Categorical mental-neutral property dualism
Categorical property pluralism.
To repeat, of the substance theses is logically compatible with each of the property theses. Permute them, and you get sixty-four possible categorical views. Of course, not all sixty-four are whatsoever plausible: for good reason, nobody thinks that both categorical mental-neutral substance dualism and categorical property physicalism are true. But this is no matter: once again, my goal in the present work is only to determine which views are options in theory.
2. Foundational Views
I also submit that there are sixty-four foundational views. Each one is the conjunction of a foundational substance thesis, which makes a claim about the sorts of substances that are fundamental, and a foundational property thesis, which makes a claim about the sorts of properties that are fundamental. There are eight foundational substance theses and foundational eight property theses views one might hold, all of which are compatible with each other in principle.
(A fair warning: This section is going to sound rather repetitive.)
Let’s consider foundational substance theses first. A good way to understand them is to take the foundational substance test.
The Foundational Substance Test
Which sorts of substances are fundamental? You can pick zero, one, two, or all three options.
Physical substances
Mental substances
Neutral substances (which are neither mental nor physical)
How many did you choose? If you chose zero, you’re a foundational substance eliminativist.
If you chose one, you’re a foundational substance monist. There are three classes of foundational substance monists. If you think that only physical substances are fundamental, you’re a foundational substance physicalist. If you think that only mental substances are fundamental, you’re a foundational substance idealist. If you that only neutral substances are fundamental, you’re a foundational substance neutralist.
If you chose two, you’re a foundational substance dualist. There are three classes of foundational substance dualists as well. If you think that physical and mental substances are both fundamental, but not neutral substances, you’re a foundational mental-physical substance dualist. If you think that both physical and neutral substances are fundamental, but not mental substances, you’re a foundational physical-neutral substance dualist. If you think that both mental and neutral substances are fundamental, you’re a foundational mental-neutral substance dualist.
Finally, if you chose all three from the list, you’re a foundational substance pluralist.
Lastly, let’s consider foundational property theses. A good way to understand these, as I’m sure you can now predict, is to take the foundational property test:
The Foundational Property Test
Which sorts of properties are fundamental? You can pick zero, one, two, or all three options.
Physical properties
Mental properties
Neutral properties (which are neither mental nor physical)
How many did you choose? If you chose zero, you’re a foundational property eliminativist.
If you chose one, you’re a foundational property monist. There are three classes of foundational property monists. If you think that only mental properties are fundamental, you’re a foundational property physicalist. If you think that only physical properties are fundamental, you’re a foundational property idealist. If you think that only neutral properties are fundamental, you’re a foundational property neutralist.
If you chose two, you’re a foundational property dualist. There are three classes of foundational property dualists as well. If you think that both physical and mental properties are fundamental, but not neutral properties, you’re a foundational mental-physical property dualist. If you think that both physical and neutral properties are fundamental, but not mental properties, you’re a foundational physical-neutral property dualist. If you think that mental and neutral properties are both fundamental, you’re a foundational mental-neutral property dualist.
Finally, if you chose all three from the list, you’re a property pluralist.
In sum, there are eight foundational substance theses:
Foundational substance eliminativism
Foundational substance physicalism
Foundational substance idealism
Foundational substance neutralism
Foundational mental-physical substance dualism
Foundational physical-neutral substance dualism
Foundational mental-neutral substance dualism
Foundational substance pluralism.
And eight foundational property theses:
Foundational property eliminativism
Foundational property physicalism
Foundational property idealism
Foundational property neutralism
Foundational mental-physical property dualism
Foundational physical-neutral property dualism
Foundational mental-neutral property dualism
Foundational property pluralism.
Each of the foundational eight substance theses is compatible in principle with each of the eight foundational property theses. Permute them, and you get the sixty-four possible foundational views. Again, not all sixty-four are plausible candidates. No one, as far as I can tell, is both a foundational substance eliminativist and a foundational mental-physical property dualist. And, indeed, no one should be. But, again, that’s irrelevant to my purposes here.
Before I proceed, it’s worth emphasizing that not all of the foundational theses are compatible with all the categorical theses—far from it. After all, it’s only possible to think that a substance or property is fundamental if you believe it exists in the first place. So, for example, you could be a categorical mental-physical property dualist and a foundational property physicalist if you thought that both mental and physical properties existed, but that only physical properties were fundamental. However, being a categorical property physicalist and a foundational mental-physical property dualist would be impossible. After all, you can’t hold that mental and physical properties are both fundamental if you only believe that physical exist at all!
3. Relational Views
Finally, any complete answer to the mind-body problem must contain a view about how substances and properties are related to one another. Those with identical categorical and foundational views may diverge. For instance, three philosophers who accepted both categorical and foundational mental-physical property dualism, might disagree about the nature of the relation between mental properties and physical properties. One might believe that mental properties are identical to the physical ones; another might hold that mental properties are grounded in physical properties, and the third might maintain that mental properties are merely supervenient on their physical counterparts.
I won’t try to taxonomize all the possible relational views. Given the number of categorical views in logical space combined with the many distinct mind-body relations that have been suggested in the literature, the possibilities are too numerous to cover. Instead, I’ll simply provide a non-exhaustive list candidate relations, not all of which are mutually exclusive:
Type identity
Token identity
Grounding
Supervenience
Constitution
Emergence
Causality
Necessitation
Functional realization
Let’s recap: Complete answers to the mind-body problem are constituted by three different claims: a categorical view that describes which substances and properties exist; a foundational view that describes which substances and properties are fundamental; and a relational view that describes the relations between existent substances and properties. Careful readers with a background in the metaphysics of mind might observe that my taxonomy makes some surprising classificatory verdicts. However, I’m willing to bite these bullets in service of accepting what I take to be an elegant taxonomical system.