This paper discusses the phenomenon of tautology appearing in the target text (primarily in the so-called theoretical discourse) at places where there is no trace of it in the source text. This phenomenon is identified as a special type of contresens, i.e. mistranslation appearing as a result of not entirely correct interpretation, mistake or negligence on the part of the translator. In the first part of the article, the author demonstrates this phenomenon with the help of particular examples. Then he goes on to draw some more general conclusions, using the tautologies found in a text translated from K. Marx an another one form M. Heidegger. The study also sheds light on the reasons for this phenomenon. One of the reasons for the appearance of the tautology, the paper suggest, may be that the author of the source text could choose form among several potential lexical variations (synonyms) in his/her language, whereas there is only one lexical item at the disposal of the translator in his/her respective language. Another reason may be an erroneous interpretation and mistranslation of a key term, concept, basic philosopheme in the source language. Consistent adherence to a mistranslation results in a sort of a trap (a tautology, an sometimes eve a case of nonsense) which the translator inevitably falls into, by having set it up himself/herself.