The core of Descartes' philosophy is rationalism. He believes that human reason can be used to discover truth and knowledge. He put forward the famous philosophical proposition "I think, therefore I am" in the book The First Philosophical Meditation.

This proposition means that we can't doubt our existence, because we are thinking, and thinking must have thinkers. This proposition is Descartes' in-depth discussion on human understanding of the world and self-cognition, and it is also an important milestone in the history of western philosophy.

Descartes' philosophical thought had a far-reaching influence on the later development of philosophy, especially on the development of modern philosophy and mathematics. His universal doubt method and the proposition that I think therefore I am inspired many later philosophers and thinkers. His thoughts also have an important influence on modern logic, epistemology, metaphysics and other fields.

Descartes' method of universal doubt;

1. Put forward assumptions: Descartes first put forward some assumptions, such as all knowledge is reliable or I am ignorant. These assumptions are the premise of his doubts and the basis of his reasoning.

2. Negative assumptions: Once we accept some assumptions, we need to find ways to deny them. Descartes denied these assumptions through logical reasoning and observation. For example, he will examine whether the information conveyed by our senses is true, or whether we are really dreaming, and so on.

3. Put forward a new hypothesis: once we deny a hypothesis, we will look for a new hypothesis to replace it. This new hypothesis must be able to explain what we have observed and let us understand the world better.

4. Verify the hypothesis: Finally, we need to verify whether the new hypothesis is correct. Descartes believes that only through constant observation and experiment can a hypothesis be verified.

5. Philosophical method: Through this method, Descartes made a profound discussion and reflection on human cognitive ability and rationality. In this way, he tried to build a solid foundation, so that human knowledge and understanding can be reliably guaranteed.