The subject of the study is the ontological meaning of Kant's question "how are synthetic judgments a priori possible?". Topic of the article: "The Kantian question as a way of self- actualization of the subject." The purpose of the study is to study the structure and existential- ontological aspects of Kant's question "how are synthetic judgments a priori possible?". The methodological basis of the research is the existential-phenomenological ontology. The scope of the research results: ontology and theory of knowledge, philosophy and methodology of science, philosophical hermeneutics. The main conclusions of the study: interpretation of the question "how are synthetic judgments a priori possible?" as a way of existential self-reflection of the transcendental subject, it allows to overcome the criticism of Kant's "tautology", undertaken, in particular, by Friedrich Nietzsche; the study of the structure of the Kantian question made it possible to identify three main points accompanying this issue: the acceptance of the free action “I think” as the primary fact of the mind, the analysis of knowledge as the content of thinking, and the conceptualization of faith as the boundary of knowledge; the ontological meaning of the question "how are synthetic judgments a priori possible?" is to make room for the free action of "I think"; the need for this release is connected with the dual "nature" of thinking, which hides its own free source behind the logical necessity of knowledge; the Kantian question, therefore, acts as a way of self- actualization of the transcendental subject.