Kant´s critical philosophy refutes dogmatism and also scepticism taken exclusively, through the criteria of the self-knowledge of reason. However, dogmatism cannot be simply surpassed. The conversion from the dogmatic posture to the critical does not exclude what is necessary in the dogmatic procedure, for reason as well as for philosophy. The same goes for scepticism. The hypothesis guiding this work is that the dogmatic procedure and the sceptical method are both necessary for knowledge; they cannot be surmounted, but must instead receive a critical version. It is right to say that the synthesis in some measure of scepticism and dogmatism in a single philosophical system characterizes modern thought. This synthesis, therefore, can be considered as a mark of modernity, and, for Kant, to oppose the sceptical method with the dogmatic procedure is a means of keeping reason healthy, and thought, vigorous, being Kant the first thinker in modernity to hold and elaborate this synthesis as a permanent task for philosophy.