From the point of view of certification mental work is established as the light one. The term “hard mental work” is not common in Poland. As far as medicine is concerned only persons without severe organic diseases and brain disorders can perform hard mental work. Other conditions that make people able to work hard intellectually include sensitivity, inquisitiveness, inventiveness, personal independence, long lasting concentration on the object of research. Such characteristics is found typical for creative individuals with their unique personality and features.