The phenomenon of transcendental subjectivity is primarily associated with the concept of transcendental unity of the apperception ‘I think’, which accompanies all representations. In order to give a complete defi nition of the phenomenon of transcendental subjectivity, it is necessary to study the relation of the unity of apperception to the pure primary passive synthesis of time. Transcendental subjectivity is the basis of the possibility of pure synthetic judgments a priori and the origin of the basic ontological categories. Transcendental subjectivity is the principle of the constitution of the world of nature as the interrelation of phenomena according to the laws of reason and at the same time — the principle of the constitution of the world of practical freedom.