The scientific method of cognition leads Descartes to the boundless confidence in the mind. However, the mind is skeptical and doubting. Actually, the path to philosophy begins from doubt. Therefore, you need to doubt all your feelings and thoughts. This conclusion follows from the first rule of the method. But then, according to the second rule, the fact of doubt will be doubtless. And if something is doubting, it thinks. So, there is something what is thinking, that is, the subject, the "I". There is one last step: "I think, therefore I am, therefore, there is a thinking thing or substance, soul, spirit". Descartes believes this thesis is the most reliable intuition, it is more reliable than mathematical intuition.
The doctrine of innate ideas appeared in Descartes’ mind after attempts to build universal knowledge. When he realized the groundlessness of his plans, the recognition of innate ideas occured. They include: genesis, God, concepts, numbers, duration, embodiment and the structure of the bodies, the facts of consciousness, free will. In addition, several judgment axioms are also innate ideas: " From nothing, nothing comes", "you cannot simultaneously be and not be", "the whole is greater than the part", "two times two is four", etc(Descartes).
Descartes tries to pre-confirm the existence of God as a necessary, in his opinion, mediating link between the "I" and the nature.He refers to the fact that God needs us as a guarantor of the existence of the world, his knowledge and generally error-free operation of the human mind, since only God could be a reliable source of "natural light", the opposite to all lies and deception. The inadmissibility of lies is the first proof of God's existence. Second proof, formulated by Descartes: only God is able to instill in the souls of men as imperfect beings, thought about the existence of an all-perfect being. The third proof may be deduced from the Descartes’ rationalism: "No one, thinking what is God, cannot conceive that there is no God"(Descartes). The last proof is very close to the medieval scholastic evidence.
All three evidences are highly questionable and logically bad provable. Apparently, feeling this, Descartes introduced one more, the fourth proof of God's existence, cleverly deducing it from the fact of the doubt. It says that under the intuition of the doubt inside us, there is the intuition of the all-perfect being. This is how Descartes closes the circle: referring to God as to the guarantor of the reliability of the principle of intuition, which generates the truth, he justifies the very existence of God by referring to the intuitive choice of mind. But an unexpected consequence follows this conclusion: Descartes made the concept of God dependent on human mind and its actions. In fact, Descartes establishes the principle of deism.
Deism means that God, though is the final cause of the world, cannot change the actual composition of the previous events, cannot do miracles and cancel laws of nature that were established by him. Therefore, creating laws and giving them to the world, God leaves and gives nature an opportunity to develop independently. Its further function is to be the guarantor of the laws of conservation of nature, knowledge of the truth and immutability of already received truths. He provides overall stability and firmness of the universe.
The reason why many are convinced that it is difficult to perceive God, or even his own soul, is, according to Descartes, that people never rise above what can be cognized by the senses. People should not use the imagination and senses to understand the nature of God.
Many of the ideas of Descartes were soon critically comprehended and developed in other philosophical system, such as the philosophy of T. Hobbes.
Descartes, René; Cress Donald. Discourse on Method and Meditations on First Philosophy (Fourth Edition). 1998