Public danger is a fundamental category of criminal law that defines its essence and social purpose. At the same time, science has not yet developed a unified view on the nature of public danger, its place and role in the structure of criminal law knowledge and law enforcement. In particular, the following questions remain unresolved: the legal boundaries of public danger, the correlation of the principle of legality with the social foundations of criminal liability, the correlation of the concept of harm with public danger, the possibility of its objective cognition, the impact on the assessment of public danger of acts of social values and personality, determining the quality of a crime. The paper analyzes the phenomenology of social perception of public danger in the aspect of law enforcement assessments of real harm. For this purpose, dialectics is used in the categories of reality and possibility. Harm is considered as a category of reality, and public danger as a category of opportunity. At the same time, the author understands harm and public danger not in a universal, but in a legal sense. The essence of harm means an encroachment on social values and a response to it from society and the state — a moral rebuke of the act, elevating it to the degree of social threat (danger). The public danger of a crime is constructed by the legislator, therefore this property (public danger) is associated with the reality of harm and is an important and necessary criminal law construct filled with real social meaning. The modern problem, actualized by the security paradigm, is the definition of moral criteria for the validity of socially dangerous harm.