The article presents Herbert Hart's theory of the truth-conditional definition as a special kind of the theory of contextual definition. It is shown that Hart not only modifies the paraphrase of Jeremy Bentham, which had a strong influence on his approach, but also tries to adapt to the analysis of legal concepts the definition in use borrowed from analytical philosophers and logicians. The key point of Hart's new method for philosophy of law of the XX century is that instead of defining a separate term, it is necessary to consider a statement, where the utterance plays a characteristic role, and it is explained by specifying the conditions under which the entire statement is true. Some difficulties that arise when one uses this definition in the framework of the truth-conditional semantics are also considered.