The Ontology of René Descartes

René Descartes is famously considered the founder of modern philosophy. As such, he ushered in a new era in an area of philosophy known as ontology. Ontology is the study of being or existence.

The ontology of Descartes is a substance-based ontology. This means that the primary elements or types of entities in his ontology are substances. Specifically, there are two primary kinds of substances in Descartes.

In this article, we’ll look at the specifics of Descartes’s ontology and what makes it unique in philosophy and metaphysics. By the end of this article, you should have a solid grasp of René Descartes’s fundamental ontological theory.

The Thinker, a sculpture by Rodin, in Paris.
The Thinker by Rodin, in Paris. Image by Johnnie Shannon from Pixabay

Who Is Philosopher René Descartes?

René Descartes (1596 – 1650) was a french philosopher, mathematician, and natural scientist. He is most famous for inventing analytic geometry and being considered the founder of modern philosophy.

Analytic geometry is also known as coordinate geometry or Cartesian (after Descartes) geometry. It is the study of geometry using the coordinate system. You, like me, may remember this from middle or high school mathematics classes.

Modern philosophy is the period of philosophy that falls after medieval philosophy and contemporary philosophy. It generally falls between the 17th and 20th centuries. Modern philosophy was then superseded by both analytic philosophy in the Anglo-American world and postmodern philosophy in Continental Europe.

Descartes’s most famous philosophical statement is “Cogito, ergo sum”. This translates to “I think, therefore I am.” This statement appeared in Descartes’s Discourse on the Method in 1637. It purported to prove that the fact that I am currently thinking proves my own existence and thus is an answer to extreme skeptical doubts that no knowledge at all is possible.

Descartes’s most famous philosophical work is Meditations on First Philosophy (1641). In the Meditations, Descartes uses rationality to attempt to establish his own existence, the existence of God and the soul, and an epistemological foundation for modern natural science.

What Is Ontology?

Ontology is the branch of philosophy that studies being or existence. It is generally thought of as a branch of metaphysics. Metaphysics is the study of reality or ultimate existence. Basic questions of ontology include asking what exists and what doesn’t exist, as well as in what way things exist, and whether there is only one way of existing or multiple different ways of existing (ontological pluralism)

Ontology questions the existence or nonexistence of a whole range of different types of entities. An entity is any existing thing or being. Some of the types of things ontology can ask about include:

  • God
  • The Soul
  • Free Will
  • Numbers
  • Abstract Objects
  • Fictional Characters
  • Time and Space
  • Physical Objects
  • Ordinary Objects

While the Ancient Greek philosopher Aristotle was not the first philosopher to ask ontological questions or to formally study ontology, his definition of metaphysics is a good definition of ontology. His definition of metaphysics (ontology in our sense) is, “a science that studies being qua being” (Aristotle, Metaphysics, IV.1). 

Let us now take a look at Descartes’s own ontological position.

Descartes’s Ontology

Substance Ontology and the Mind-Body Distinction

Descartes’s main ontological distinction is that between mind and body. This is often known as the “mind-body” distinction. According to Descartes, minds and bodies are two different types of substances with two different essential properties. The essence of mental substances is that they are thinking things while the essence of bodily substances is that they are extended in physical space.

For Descartes, thought and extension are the substance-defining attributes or essential properties of mind and body respectively. But, thought and extension can each have different modes of being. 

Different modes of thinking include:

  • Judging
  • Willing
  • Desiring
  • Doubting
  • Sensing
  • Perceiving
  • Imagining
  • Feeling

Modes of extended embodied things can be any physical shape that a body can be made into, including the shape of a stone, a tree, a bench, a sheep, or a person.

Substances and Modes of Being

For Descartes, substances and modes have different degrees of being. This degree of depends on whether or not the entity can exist independently. For Descartes, substances have more or a higher degree of being than modes. This is because substances  – like individual minds or individual human bodies – don’t ontologically depend on anything else for their existence.

On the other hand, modes of being do depend on substances for their being. You can’t have thoughts, willings, or emotions without a mind. You can’t have the shape of a park bench without an actual park bench for it to inhere in.

Philosophy of Mind and Substance Dualism

Descartes’s philosophy of mind is generally known as substance dualism. Substance dualism is the belief that minds and bodies are two different substances. It is contrasted with substance monism, which claims that everything is the same substance – either everything is physical, or everything is mind.

Substance dualism argues that because mind and body are distinct substances, they can technically exist separately from one another. So in theory, a human mind or soul could be separated from a human body. This can be convenient if you also believe in an afterlife in which your body dies but your soul goes to heaven or hell.

Of course, while we are alive our body and our mind are generally quite intertwined in Descartes’ view. Descartes doesn’t speak on the subject of astral projection or out-of-body experiences, which would seem to be cases of a separation of mind and body if they are true.

Substance Dualism and Causal Interaction

One problem with Cartesian substance dualism is that it is difficult to explain how two different substances like a mind and a body can causally interact with one another. If mind and body are indeed two different substances, it seems inarguable that the two must interact with one another.

For example, let’s say I desire a glass of water and so I reach out for a glass in front of me and drink. It seems undeniable that my mental desire caused my physical bodily action of taking the glass and drinking.

On the other hand, let’s say I am going through a stack of papers and receive a paper cut. In addition to the physical injury and bleeding finger, I also have a mental sensation of feeling pain. That mental sensation of pain is almost certainly caused by the physical act of cutting my finger on the paper.

But if minds and bodies are so distinct from each other such that minds are not bodies at all and bodies don’t think, how can one possibly causally affect the other? Why would a physical action cause a mental sensation? Why would a mental desire cause a physical reaction? It’s extremely hard to explain how these two seemingly intertwined but completely different types of substances affect one another.

If you enjoyed this article about Descartes’s ontology, make sure to check out my recent article on Spinoza’s ontology.

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