Immanuel Kant, one of the most significant thinkers of the Enlightenment, on the premises of the Copernican turn, develops a theory of cognition that puts at the center of thinking a rational subject, who through the mind, as a framework of human knowledge, cognizes the outside world. Kant's theory of cognition on one hand unites, while on the other, rejects the theses of both rationalists and empiricists: despite Kant's claim that one can attain knowledge about the world through interaction of cognitive abilities of both mental and sensory nature, at the same time, he assumes that one can never grasp the literal picture of the world, as it takes shape in the human mind only in the form of mental images - phenomena, a thesis that Kant calls the metaphysics of the transcendental idealism. To that extent, Kant does not explore the conditions and limitations of empirical reality, but instead turns to the analysis and categorization of the conditions of linguistic reality, which as such is the only framework that provides us with forming true and justified beliefs about the world: Kant's cognitive theory is based on the evaluation of judgments as propositions according to which one can form possible knowledge about the world. Thus, the most significant achievement of the Kant's Critique of Pure Reason is the classification of judgments as true propositions, whose logical form, semantic and syntactic content, enable the expansion of human cognition within the limits of phenomenological reality, while claiming that the truth of the latter classification is justified if and only if the theory of transcendental idealism is accurate. In this paper, Kant 's theory of cognition is presented, as well as possible challenges both for the classification of judgments in particular and the premises of transcendental idealism in general.