Descartes was in search of a sure foundation of knowledge

Descartes was in search of a sure foundation of knowledge, a first certainty that could serve as a foundation for all philosophy and science. Cartesian doubt is a method, that leads to certain and undoubted knowledge. Sensible doubt, the doubt of the dream and the metaphysical doubt. The sensitive is the one that leads us to distrust the senses and all that we learn through the senses. The doubt of the dream is the one that shows us that we cannot be sure that we are awake or dreaming at that moment. What I have learned Descartes was not a neurotic who suffered from an obsessive thought of doubt, but a philosopher who used doubt as an instrument in his journey in search of the foundation of knowledge. Reading about Descartes methods of doubt I learned that are many types of knowledge, but the most important are the scientific knowledge is a real knowledge because it deals with occurrences or facts, it constitutes a contingent knowledge and the empirical knowledge is what we acquire during the day (pag95, paragraph5).
Descartes experiments with the piece of wax to prove what is conceived in his spirit about this body. Descartes will conclude that wax, this external body, subjected to sensitive experiments in its materials and substances – itself, the wax – is still only a wax Descartes admits that what remained for him in his spirit was the same wax: “It must be admitted that it remains, and no one can deny it”. Surely it can be absolutely nothing of all that observed through the senses, for all things that fell under the palate, or the smell, or the sight, or the touch, or the hearing, are changed, and yet the same wax remains. Then he concludes that his senses have perceived the wax differently, but have something that remains; however, what remains of that body is the same wax. (page176, paragraph 3)
What I have learned after reading Descartes is that he would apply to all corporeal bodies of the type of wax the same understanding, saving true men in the second situation: when he sees them through the window he understands that they are true men only by the power to judge that he resides in his spirit. Also learned that the only element which differentiates the body from bodily nature from the wax-piece of the body of corporeal nature of true men, is the power of judgment of the thinking.
About knowledge I learned that it is divided a series of categories: sensory knowledge, which is the common knowledge between humans and animals; intellectual knowledge that is the reasoning, the thought of the human being; popular knowledge that is the form of knowledge of a given culture; knowledge that are evidence-based analyzes; philosophical knowledge that is linked to the construction of ideas and concepts and the theological knowledge that is the knowledge acquired from faith.