The text shows that Alfred Tarski studied semantics to define a true sentence in a materially adequate and formally correct way, and in effect he defined the co-called semantically closed languages as a subset of formalized ones, in which the occurrence of the Liar paradox is imminent because of the features of the language used. This is one of the points of Tarski’s heritage where misunderstandings constantly occur among the readers of Tarski‘s work, and that is why the present paper may prove to be useful by presenting suitable excerpts from the original Tarski’s text. Tarski found additional limiting criteria applicable to formalised languages, which may prevent the appearance of the Liar paradox hidden inside the paradox itself. They deal with self-referring expressions which occur in natural languages even more frequently than the sentence „John loves Mary”, which is only sometimes true.
The journal founded by Leszek Kołakowski, Bronisław Baczko and Jan Garewicz appears continuously since 1957.