The paper deals with the factual, theoretical-linguistic and inter-disciplinary argumentation of the existance of the archaic, extinct and understudied linguistic phenomenon registered in a number of synchronically documented and diachronically non-documented languages of the North Asian indigenous ethnic languages – the grammatical marking of a non-observable speaker, i.e. non-observable speech acts. To the author’s knowledge, the available linguistic facts testifying to the existence of the phenomenon in question can only be found in the Samoyedic traditional texts (Nenets, Enets, Nganasan, Selkup) and Yukagir texts. Nevertheless, these facts have never been pointed out and have been outlined in a differing degree of informativeness. This is the fact underlying the way of reasoning in this research. The materials of the study are based on the traditional Tundra Nenets folklore texts which are most informative. The analysis of the Nenets language materials has made it possible to reveal and substantiate the facts of the grammatical marking of non-observable speech acts in a number of other Samoyedic and Yukagiric languages and to trace the possible similar facts in some other languages of North Asia.