This article concerns the concept of fallacy in its dialectical relation to truth in scientific under­standing. It highlights a variety of definitions attempting to clarify the meaning of fallacy, which is ground zero for the authors’ definition of the aforementioned concept. It is stated that fallacy is the necessary step towards truth. It is explained why fallacy cannot be identified with incomplete knowledge, logical fallacies and falsehood. Also, this article highlights the main doctrinal philosophical and methodological foundations of fallacies and criteria for defining the truth.