The moral law and the idea of freedom are the core concepts of Kant’s ethics. Through consideration of this concept, this study revealed what Kant has done in the field of ethics. Kant revealed that there is ‘the cause of freedom’ in humans, and that the cause of freedom is a ‘logical cause’ in that it is a regulation in the practical aspect of ‘pure reason’. What Kant did in the first critique revealed that human cognitive behavior contains ‘pure reason’ as an a priori condition of perception that is not explained only by sensory experience, revealing the metaphysics in epistemology. What Kant did in ethics was reveal that it is none other than metaphysics as a ‘practical use of pure reason’ that enables human moral behavior by revealing the idea of freedom as the basis for the establishment of moral behavior. Based on this, this study examined the characteristics of the second critique seen in relation to the first criticism. Given that the first critique is Kant’s metaphysics, which deals with the outline and fundamentals of the entire system of Kant’s philosophy, and the second critique is Kant’s moral philosophy, which deals with Kant’s ethical criticism in earnest based on the first critique it was discussed that the two critique are related to the metaphysical foundation of Kant’s ehics and that they are also related to epistemology and ethics and metaphysics. Furthermore, this discussion also revealed that its justification can only be secured from a metapraxis perspective (from the perspective of heart cultivation).