What does substance dualism say?

What does substance dualism say?

Frans Hals – Portret van René Descartes

Substance Dualist Position, or Substance Dualism, is a set of philosophical ideas that answers the question of the mind-body problem. The idea of Dualism, or mind-body, was first brought by Plato. There exist several Dualist positions in the long history of philosophy. Substance Dualism is one of them, and the definition of Substance Dualism was improved and famously defended by French philosopher René Descartes, in philosophy, Descartes’ defense of Substance Dualism is called Descartes’ Conceivability Argument. His arguments consist of several connected premises: 1) “I am thinking and I have no body”; 2) “I am thinking and I do not exist”; 3) “I exist and I have no body”.1 

The fundamental idea of Descartes’ Conceivability Argument states that humans consist of two main substances.

These substances: the self, mind, or soul lets mention as mind. Moreover, the body. Of which, the mind is immaterial, and the body is physical; the body cannot think on its own. Instead, it is the mind that is thinking. Notice that, the very foundation of Descartes’ Conceivability Argument is that the mind is a substance. In Descartes’ argument, a substance defines as an individual component that possesses properties. For instance, according to Descartes, one property of mind is that the mind is able to think; a property of the body is that it has weights/mass. 

Though Descartes’ Conceivability Argument for Substance Dualism consists of well-defined premises. There still exist some theoretical flaws improved and some concepts that are yet to be clarified.

Richard Swinburne, an English philosopher and a defender of Substance Dualism, in his paper “Cartesian Substance Dualism”, points out many logical loopholes in Descartes’ Conceivability Argument. Also in this paper, he provides many supporting arguments that help “repair” the loopholes and help clarify some ambiguous concepts in Descartes’ argument. First, Descartes uses the word “conceive” in his arguments several times.

However, the meaning of the terminology is not so obvious within the context. Swinburne helps readers understand Descartes’ argument by clarifying the word “conceive” as following: “… ‘conceivable’ means ‘logically possible,’ understood as ‘does not entail a contradiction’… to conceive a proposition is then to suppose of a conceivable proposition that it is true.”

For example, Newton’s law of gravity states that every object attracts every object.

While it is conceivable that Newton’s law of gravity might be false. Empirically, fairly obviously no contradiction entailed by supposing our universe to be like this. Secondly, Swinburne points out that Descartes’ argument lacks a clear definition of what a substance is. He then provides a definition of substance in Descartes’ context; a substance is an individual component of the world which has properties.2

Also, Swinburne suggests that in Descartes’ argument, the definition of “substance” and “property” need to be supported and well-illustrated by providing examples. For instance, the desk is red, which means the substance desk has the property of red color. Third, Swinburne insists that Descartes needs a principle stronger than the first principle that “I am thinking and I have no body” is conceivable. What he needs is the principle that “While I am thinking now, my body is suddenly destroyed” is conceivable,3in other words, it is conceivable that when the body is suddenly destroyed, the mind is still able to think. Thus, Swinburne concludes his argument for Substance Dualism as humans consist of two substances: 1) the mind/soul, which is essential and immaterial; 2) the body, which is inessential and physical. 

As stated earlier, there exist several Dualist positions in philosophy.

Portrait of René Descartes, bust, three-quarter facing left in an oval border. [Still image]: [print]

In addition, there are also ideas that are against Substance Dualism, or non-Dualist ideas. Of which, Strong physicalism and Property Dualism are the most popular two. Jaegwon Kim, a Korean-American philosopher, in his work “Against Cartesian Dualism,” provides his definition of these two sets of ideas. Furthermore, he also brings out several well-grounded arguments that are objections to Substance Dualism. One of which is the idea of “Contact Requirement.”

In his paper, (given minds are immaterial, that is, minds have no spatial extension. And are not located in physical space. Kim undermines Descartes’ Conceivable Arguments by asking the following critical question:

If bodies can be moved only by contact. How could an unextended mind. Which is not even in space. Come into contact with material things. Even the finest and lightest particles of “animal spirits,” thereby causing them to move?

This question was originally asked by one of Descartes’ pupils. Descartes’ response to his student says that the idea of mind-body is a “primitive notion.” Kim forms his argument by extending this response. The major point in his argument is that our mind can cause other minds or bodies only by causing our body first, and nothing can cause our mind without causing our body first. In other words, contact with our body needs to be made in order for our mind to be affected. Same way around, our mind can only have causal power when our body makes contact with another body. Hence, mind and body are one thing, or there is no such thing as mind-body Dualism. 

In regards to Kim’s objection to Substance Dualism, at first, I want to recognize that Kim’s arguments and premises are well backed by logic. However, I do not think his objection is convincing enough. One key reason is that, in Kim’s argument, he undermines Descartes’s argument assuming that the Contact Requirement is true without providing any rigorous proof. Besides the light switch example we covered in lecture, there still are many instances in our life that are contradictory with the idea of the Contact Requirement and therefore prove such an idea is false.

Take the magnetic field as an instance, when particles are moving in magnetic fields, there does not exist any form of physical contact. From this perspective, I have reason to believe that Kim made a basic reasoning mistake. In which he uses an idea that is yet to be well proved and accepted both empirically and theoretically. Thus, I do not think Kim’s objection does not successfully undermine Substance Dualism. (Word count: 1018)

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Frank Wilczek

What does substance dualism say? Works Cited 

Kim, J. Against Substance Dualism. 


Swinburne, R. (2013). Cartesian Substance Dualism.

What does substance dualism say?