I say things like “I am hungry” or “I am thinking”. It seems that when I speak this way I am attributing mental states, such as being hungry and thinking, to me – a person. But what is the nature of this thing called a person? Is a person just a certain physical body, or some physical part of it, such as a brain, as some philosophers believe? Or, is a person something other than his or her physical body, a view held by philosophers called “dualists“?
Dualism says that a person is not to be identified with his or her physical body, or any part of it. But dualists are divided about whether a person has physical properties, such as shape and location in space. Let us say that a “soul” is a non-physical thing – which some people believe exists, and think is crucial to my being a person and having mental states. Then our three versions of dualism disagree on what role (if any) a soul plays in what makes me a person. Here are three versions of dualism.
Soul Dualism = A person is simply a soul, that is related in some way to a certain physical body. The body is not part of the person.
Hybrid-Soul Dualism = A person is a combination of a non-physical soul and a certain physical body.
Non-Soul Dualism = A person has no soul, and has physical properties, but is not identical to a certain physical body or any part of it.
Each of these three versions of dualism agree that a person is the subject of mental states. Each of these three versions of dualism deny that a person is just a certain physical body, or some physical part of it, such as the brain.
Many people find soul dualism appealing because it makes it possible that a person can survive the death of his or her body. Soul dualism allows for the possibility of surviving either as a disembodied soul or as a reincarnated soul. Hybrid-soul dualism and and non-soul dualism don’t allow for the possibility of a person surviving as a disembodied soul. However, they do allow for the possibility of reincarnation. If your body dies, it’s possible that you will survive in a different body, perhaps an angelic one.
The soul is to be understood as something simple, not made up any sort of stuff, that can undergo changes through time. It is what supports (or “houses”) mental states. Which mental states? Some soul dualists believe that all of your mental states are states of your soul, whereas other soul dualists believe that just some of your mental states, such as thoughts, are states of your soul and that some of your mental states, such as your bodily sensations and perceptions, are states of your body. As I continue to discuss soul dualism, I will assume that a soul supports all mental states, including bodily sensations and perceptions.
Souls are not physical. They do not have shape or weight or location in physical space. They cannot be directly observed with any of the senses. In contrast, my body, which is physical, has shape and weight and location in physical space and can be directly observed. You can see or hear or smell or taste to touch my body. Even my brain can be directly observed if my skull were opened up.
Philosophers who deny the existence of souls have no issue with anyone who uses the word “soul” in expressions like “the eyes are a window to the soul” or “that person has a very old soul”. They just think the word “soul” in these expressions refers to a person’s personality, not to something non-physical distinct from your body.
If a soul is the subject of experience and it’s not physical, then a person’s mental states are not physical. Do the nonphysical mental states of a person causally interact with the physical states of that person’s body? The answer depends on which dualist you ask. Some dualists believe that nonphysical mental states cannot causally interact with anything physical, including the physical states of a person’s body. However, many dualists called interactionist dualists believe that a person’s nonphysical mental states and the physical states of his or her body can and do causally interact with each other.
Assuming that I have a soul, here are some examples of how my nonphysical states and physical states of my body causally interact.
Mental State to Physical State Causal Interaction: If you choose to move your arm, then it’s because your desire (a nonphysical mental state of your soul) is causing something physical in your body.
Physical State to Mental State Soul Causal Interaction: If you feel water on your hand, it’s because something physical in your body is causing you to feel a certain sensation (a nonphysical mental state of your soul).
Dualism does not conflict with what science has taught us about the relationship between mental states and brain states. In the 1950s the neuroscientist Wilder Penfield showed that by stimulating parts of the brain with an electrical circuit, it was possible to elicit memories in the subject. We also know that damage to the brain can cause problems with a person’s mental states. To help appreciate this connection, read this article and then watch this video and this video. The interactionist dualist believes that the brain plays a fundamental role in mediating the causal interaction between mental states and the body: the brain both enables a person to experience the physical world, including what’s going on in his or her body, and it enables a person to move his or her body.
Although an interactionist dualist who believes in souls has an answer as to why we need a brain for moving our bodies around and experiencing things in our environments, including our bodies, it’s not entirely clear what explanation he or she can give for why we would need a brain for reasoning – e.g. doing mathematics. Why, for example, would damage to a certain area of the brain cause problems with reasoning if reasoning happens in the soul? Some philosophers believe that since damage to the brain causes problems for reasoning, any dualism that says reasoning is done in the soul is not an adequate theory.
If a person is not entirely physical, as the dualist believes, then he or she may not be subject to the laws of nature. In contrast, physical bodies are subject to the laws of nature, such as the law of gravity and genetics. Some dualists believe that it is because a person is not subject to the laws of nature that a person can make free choices. These dualists believe that if a person were entirely physical, like a computer, he or she wouldn’t be able to freely choose. So if you believe that you do freely choose and you believe that purely physical things, like a computer, cannot freely choose, you should find dualism an appealing view. In a later post we will discuss whether you can freely choose if your actions are subject to the laws of nature. You may think the answer is obviously “no”. But many philosophers believe that something entirely physical, such as a computer, can freely choose.
If dualism is true, then a person is something distinct from his or her physical body. You many wonder whether dualism is true for non-persons. Is it true for chickens, or mice, or mosquitoes? You may also wonder when dualism is true. Is it true at the moment of conception? Is it true when an organism is a fetus? Is it true some time after birth when there is a certain kind of thought?
