Abstract
This article considers the formal unity of the system of law. In a formally unified legal system, there is in principle no doubt about which rules fall within the system and how to determine their content.
The author tries to show how the formal unity relates to judge's duty to law (Art. 95 of the Czech Constitution) and to the concept of the source of law. Special attention is paid to the rule of recognition and its ability to ensure formal unity of law in the situation of regulatory "outsourcing" to other social sub-systems.