Descartes’ Philosophy: Reason, Doubt, and Existence
Descartes: The Universe of Rationalism
Descartes sees the universe through the lens of rationalism. The unity of reason and science is paramount. The method Descartes uses is another matter. There is no human wisdom that remains identical, even when applied to various sciences and diverse knowledge. Incremental manifestation of knowledge is the only reason for Descartes.
The Structure of Reason and Method
Descartes identifies two types of knowledge: intuition and deduction.
- Intuition: A light or natural instinct. It involves simple natures as an object, through which it immediately grasps the simple without concepts, avoiding error.
- Deduction: Insights from the succession of simple natures and simple connections.
Knowledge can be explained in a two-step process:
- Rules of method:
- Evidence-analysis: Reaching simple elements.
- Synthesis: Deductive reconstruction from the simple.
- Concrete enumeration: This form is the only method that responds to the internal dynamics of reason.
Doubt and the First Truth
Methodical doubt: Understanding itself requires basic truths from which it is possible to deduce the whole edifice of knowledge. The starting point must be absolutely true. Descartes begins by analyzing knowledge and removing all that can be doubted. Doubt begins with this and is methodical, demanding method in the analytical time.
Descartes proposes three reasons to doubt:
- The fallacies of the senses, which sometimes induce error.
- The failure to distinguish between wakefulness and sleep.
- The existence of an evil spirit that makes every effort to induce error, which is equivalent to supposing that human understanding is always and necessarily mistaken when it wants to grasp the truth.
The First Truth and the Achievement Criterion
After much time, Descartes reaches an absolute truth: the existence of the subject who thinks and doubts. “My existence is the prototype of truth and is certainly perceived with clarity and distinction. Everything I clearly and distinctly perceive is true.”
Ideas
Ideas are the object of thought. The existence of self seems to imply no other reality, but how do we demonstrate the existence of a reality external to thought?
- The problem is huge. Descartes has no choice but to infer the existence of reality from the idea of thought.
- Two elements:
- Thinking activity (I think).
- Ideas.
Descartes concludes that thought always involves ideas. The notion of “idea” changes in Descartes’ philosophy compared to previous thought.
- For previous philosophy, thought rests not on ideas but on things.
- For Descartes, thinking rests on ideas, not on things.
The real picture is a mental act objectively, and ideas are mental acts. These acts have the same reality (modes of thought), and as content, they have a goal; their reality is different.
There are three kinds of ideas:
- Adventitious: Those that come from our external experience.
- Factitious: Those that the mind constructs from other ideas.
- Innate: Those not covered in the previous categories, so they are inherent in thought itself.
The Existence of God and the World
Among innate ideas, Descartes discovers the idea of the infinite, which he identifies with God. Once this idea is established, the deduction is expedited.
God’s Existence
God’s existence is based on the idea of God. Descartes uses a causality argument applied to the idea of God. The idea of an infinite being requires an infinite cause. Since I am not infinite, an infinite being must exist.
World’s Existence
The world’s existence is demonstrated by Descartes from the existence of God. If God’s existence cannot be demonstrated, the existence of the world cannot be demonstrated either. God is infinitely good and true; He would not deceive me into believing the world exists if it did not. Therefore, God guarantees that my ideas have an extra-mental reality. The world is extension and motion.
The Structure of the Three Substances: Reality
God is infinite substance, I am thinking substance, and bodies are extended substance.
Concept of Substance
Substance is anything that does not need anything else to exist (this can only be applied to God in an absolute way).
Body and Soul
Descartes states that body and soul, thought and extension, are different substances. This is to safeguard the autonomy of the soul concerning matter.