With this, he attempted to prove the existence of the Cogito, of God and dualism of the mind and the body, the methodic doubt as his primary grounding to prove the truthfulness of his claims. Let us now then analyze the seemingly problematic suppositions Descartes posits. One is dualism of the mind and body. It is because it is hard to conceive how two different things interact with each other. One indicator of such is when the mind chooses to do a specific action and the body seems to willingly do the action the mind chose.
Another is when we perceive objects in the external world, our mind grasp and process the forming of these images based on our sense perception. Nevertheless, the primary question one can posit on the whole philosophy of Descartes is the appropriateness of granting existence to the conceptual entities in the mind. Existence, for Descartes, is proven through the recognition of the mind based on intuitions which manifest clarity and distinctness (or inner awareness where the mind and body are inseparable yet different from each other).
By clarity, he claimed that it is the presence of an idea/object, and by distinctness, it is the relationship of clear ideas/objects and how its relationship distinguishes what belongs to an idea/object. Furthermore, he also claimed that substances are the building blocks of reality, categorized into two: the mind and the body. As such, he further maintained that these substances have primary attributes: the mind which is thought and the body, the extension. Ideas, for Descartes, are the modes of thought that link the mind and the world because they have formal and objective reality.
By the former, he meant the kind of reality things have in this world and by the latter, the reality of objects represented by ideas. Hence, an idea can have formal reality because it is the mode of thought itself and it can also have an objective reality because it represents something outside of itself. In his work, one can deduce that he is certain only in his existence. As such, making him a thinking substance. He asserted that he comes to know this fact through clear and distinct perception, and logically it would follow that all his other clear and distinct perceptions are true in reference to formal and objective reality.
In order to confirm the truthfulness of these clear and distinct perceptions, he proved the existence of a benign God which relies on the Mediators cognition of clear and distinct ideas. Even if we exempt the possibility of granting existence to fictitious entities for we may have clear and distinct perception of them, the possibility of granting existence to other conceptual entities in our mind is still questionable. First, I believe that we can only have clear and distinct perception of the conceptual entities through our senses that is they exist in the physical realm.
By that, I mean that we can have conception and understanding (on the context on how can we know them) primarily because they have manifestations in the physical world as also with regards to certain logical principles. For example, my understanding or even my idea of a tree originates from my perception of that tree in reality. Second, even if I can have clear and distinct perception of a God, it does not mean that a god/God indeed exist which cause my idea of God as what Descartes claimed.
Arguably, there may be some other entity or there may be the possibility this world is just made up of matter and energy. Hence, there is no higher being which exists. It can be deduced then the appropriateness of granting existence to conceptual entities in the mind only comes if we could know their truth in the physical realm. As such, Descartes claimed of the mind being non-erroneous in granting existence to things/objects in this world is held in question.