Descartes’ Rationalism: Method, Doubt, and Innate Ideas

Posted on Jan 23, 2025 in Philosophy and ethics

Descartes and Rationalism

The Unity of Reason and the Method

The Unity of Knowledge and Reason

Descartes aims to establish the unity of science. Because wisdom is singular, reason is also singular: the *ratio* that distinguishes the true from the false. Reason, therefore, is one and the same.

The Structure of Reason and the Method

Reason is the only method to know its structure and its operation, so as to apply it properly and thus attain true knowledge. It involves:

  1. Intuition: A “light or natural instinct” that pertains to simple natures arising from reason itself, without any possibility of doubt or error.
  2. Deduction: Displays all intellectual knowledge from the intuition of simple natures. Among other simple natures are some insights and connections that intelligence acquires, and deduction runs through them.

As intuition and deduction are the internal dynamics of knowledge, they are applied in a two-step process that refers to the second and third rules:

  1. A process of analysis down to the simple nature elements.
  2. A process of deductive synthesis, rebuilding the complex from the simple.

Doubt and the First Truth

Methodic Doubt

The mind has to find the basic truths from which it is possible to deduce the building of our knowledge. It must be an absolutely certain truth that cannot be doubted by any means; the whole system would then be firmly established. We must remove all knowledge, ideas, and beliefs that do not appear equipped with absolute certainty. Methodical doubt is a requirement of the method in its search for an absolute foundation of truth. Descartes leads to the question, even the most radical:

  1. The first and most obvious reason to doubt our knowledge is in the testimony of the senses, which sometimes leads us to error.
  2. The second reason for doubt is the impossibility of distinguishing between sleep and wakefulness.
  3. The impossibility of distinguishing between sleep and wakefulness casts doubt on the existence of things and the world, but it seems not to affect certain truths, such as mathematics. It is necessary, in a last step, to radicalize the reasons for doubt, and thus Descartes raises the hypothesis of an evil genius.

The First Truth and the Criterion

Up to this point, certainty seems doomed inevitably to skepticism. However, Descartes found an absolute truth, immune to any doubt, however radical it may be: the existence of the subject itself that thinks and doubts. I can doubt everything, but the fact that I doubt, that I exist as a subject that thinks, is exempt from all error and all possible doubt. “I think, therefore I am” (*Cogito, ergo sum*). My existence as a thinking subject is not only the first great truth and the first certainty, but it is also the prototype of all truth and certainty. Its criterion of certainty is whatever is perceived with clarity and distinction is true and therefore will be affirmed with unshakable certainty.

Ideas

Ideas as Thoughts

To infer the existence of reality from the existence of thought:

  1. That I think, the existence of which is undoubtedly true.
  2. The world as a reality external to thought, whose existence is dubious and problematic.
  3. Ideas of the world and existence that I undoubtedly possess.

Thinking always involves thinking about ideas. To previous philosophy, thought rests not on ideas but directly on things; to Descartes, it is the contrary.

The Idea: Objective Reality and Mental Act

  1. Because ideas are mental acts, all ideas have the same reality.
  2. Because ideas have objective reality, their content is diverse.

Types of Ideas

  1. Adventitious ideas seem to come from our external experience.
  2. Factitious ideas are built by the mind from other ideas.
  3. Some ideas are neither factitious nor adventitious; they cannot come from outer experience or be constructed from others. The only answer is that thought itself possesses them, that is, they are innate.

With innate ideas, we come to the fundamental affirmation of rationalism: that the primitive ideas from which the edifice of our knowledge is to be built are innate. Innate ideas are those of thought, and they are not constructed or caused by experience.