The article reveals the importance of combining the moral basis and the formal content in the nature of law. The practical significance of German legal philosopher Robert Alexy’s theory of the dual nature of law is investigated. Duality presupposes that law necessarily includes both real, or factual, and ideal, or critical, dimensions. The actual dimension is represented by elements of official origin and social efficiency, while the ideal dimension is expressed in the element of moral correctness. Accordingly, the thesis of the dual nature of law presupposes non-positivism. Importance is being increasingly attached to the question of the conformity of legal certainty and correctness of the content of norms, which is connected with the principle of justice, requiring that the decisions of the authorities are morally correct. The principles of legal certainty and justice can often conflict with each other. However, no principle can displace another one under any circumstances. On the contrary, the dual nature of law requires that both of these principles be applied in correct proportionality and be balanced. And this seems possible only in the political form of democratic or discursive constitutionalism. Constitutional rights and democracy are the main elements of constitutionalism. They are mandatory in the discursive theory and both are dual in nature. Positivism has the weaknesses of legal certainty (openness of language, the presence of conflicting norms, the dynamics of social life, etc.).But they become strong arguments for the protection of human dignity, rights and freedoms. It is the orientation of the right to its further humane development, to its “humanization”, based on the need to protect people based on justice, equality and freedom, that can be an argument filling the weaknesses of legal certainty. Then, and only then, the principle of formal legal certainty of the law is transformed into legal certainty as a component of the rule of law, which characterizes the stable and civilized development of the legal framework.