The aim of this article is to detect and clarify the problem in Aristotle's and Thomas Aquinas's transmission of forms theory, which led to its rapid abandonment in the 14th century. The author uses the original texts of Aristotle and Thomas Aquinas, as well as modern historical and philosophical studies. Detection of the problem requires not only the involvement of methodology of textological analysis, but also the use of modern epistemic logic tools. The author also uses modern ways of belief report writing. Aristotle in De Anima put forward a theory in accordance with which external objects become known through a transmission of forms. This theory leaves unanswered the question of how the form of a real thing can be in the realm of the mental. This question put many medieval philosophers into confusion. Therefore, despite the fact that among the proponents of this theory was Thomas Aquinas, this theory in the Late Middle Ages was supplanted by other theories. However, none of the scholastics could precisely indicate the reasons of the impossibility for the real thing to be present in the realm of the mental. This article fills this gap. At the beginning, the key points of Aristotle's version of the transmission of forms theory are indicated. Then a much more detailed version of this theory proposed by Thomas Aquinas is considered. Finally, it is shown that using the notation adopted in modern epistemic logic, one can deduce a contradiction from the premises accepted by Aristotle and Thomas Aquinas. The author's proof of presence of a contradiction in the transmission of forms theory is as follows. The cited texts of Aristotle and Thomas Aquinas testify that the object of thinking (species intelligibilis) in their doctrines has an abstract nature: it only encodes characteristics that are "voluntarily" attributed to it by an act of thinking As a result, the object of thinking - as it was defined by Aristotle and Thomas Aquinas - cannot coincide with the real object. In the course of the study, the author came to the following conclusions. (1) Aristotle's and Thomas Aquinas' transmission of forms theory is inconsistent, since it implies the identity of a real object with a mental one, which, in turn, under certain acceptable conditions leads to a contradiction in belief report writing. (2) This inconsistency has a much more sophisticated character than some contemporary researchers of Aristotle believe. (3) The identification of this inconsistency is in the wake of skeptic arguments for impossibility for one person to think of a real object, or to think of a mental object of another person.
