Abstract
After a cursory description of three stages of manifestation of liberty on the level of human being, as liberty of thinking, of expressing and of acting, the paper present three modes of defining the cencept of liberty and his opposite, the concept of constraint, in the languages of deontic logic: in Wright's standard logic, in our deontic praxiological system and in Hintikka's quantificated deontic logic. Two previously proposed axiomatic system of liberty and constraint are discussed. Finally, concept of liberty is defined in Hintikka's basic semantics of norms.