This article presents the reasons for the use of obligatory defense, reffered to in art. 79 of the Polish Code of Criminal Procedure, especially in § 1 p. 4, from a linguistic perspective. Art. 79 k.p.k. contains phrases undetermined which describe the mental health of the accused. Their identification in a criminal trial obliges the court to appoint an official defender. The author considers the linguistic correctness of these indetermined phrases.