The likeness and differences in contents of the notions of untruth, lie and deception are analysed. There are two points of interests: sets, attitudes, intentions of a person passing an information concerning another person; the degree of information's correspondence to reality. Untruth is defined as an utterance based on an error or inadequate knowledge of the circumstances. The lie is conscious deformation of known truth. Deception is half-truth provoking a listener to make wrong conclusions out of correct facts.