Descartes' Philosophy: Doubt, Self, and the Nature of Ideas

Descartes' Philosophy: The Nature of Ideas and Reality

The Thinking Self: Res Cogitans

I am a thinking thing: a spirit, an understanding, a reason. I possess an absolutely certain truth: the existence of the self as a thinking subject. This truth does not seem to imply the existence of any other reality, because, though I think, perhaps the world does not exist in reality.

The object of thought consists of ideas; thought does not rest directly on things, but on ideas.

Universal Methodical Doubt and Undeniable Reality

Universal methodical doubt has led to an undeniable reality: the existence of a thinking being, i.e., a substance that thinks, a res cogitans, a soul.

Descartes concludes that I can doubt the existence of a body and the world around me because I receive information through the senses, and the senses are unreliable. However, I cannot doubt the existence of my thoughts, my ideas, my subjectivity.

Defining Subjectivity

What is my subjectivity? It is the set of thoughts, ideas, representations... flowing within my self. But we have no assurance that these subjective representations (i.e., one's mind) necessarily correspond with facts from the outside world. For example, does the idea I have of my body correspond with reality? I do not know with certainty, since all the information I have about my body comes from the senses, which Descartes has decided to doubt.

The Challenge of Objective Knowledge

So, the great challenge that Descartes must overcome is finding a way to know that my ideas about the world are not dreams or illusions; i.e., whether there are objective things and how they relate to the different ideas I perceive.

Classifying Ideas: Descartes' Framework

Now, what exactly are these ideas? Descartes studied and classified them as follows:

• Adventitious or Acquired Ideas

  These are ideas derived from sensory experience, my perception of the world, or teaching. These ideas can easily be wrong, because we often have different ideas about the same external object: the Sun appears as a small, hard light, but in the mind of an astronomer, it is something very different.

• Factitious or Artificial Ideas

  These are the ideas that we invent or manufacture ourselves arbitrarily. For example, the idea of a mythological animal called a centaur is an illusory idea.

• Innate or Natural Ideas

  These are ideas that do not originate from external objects or are constructed by us, but rather emerge from the very faculty of thinking itself. They are ideas that our mind grasps and must necessarily accept without being able to alter them. The idea of God is the most prominent innate idea; other innate ideas include the concepts of cause, substance, or number.