The author responds to the considerations expressed mainly by E. A. Plesh-kevich in his article “On documentology and its methodology”. The author praises Pleshkevich’s acknowledging the concept of “documentology”. Indeed, the term “document” differs pertaining to the subject (substantially) and object (functional-ly), and this representation makes the foundation for relativeness of this concept in practical applications. Meanwhile, the author points to the disruptiveness of other Pleshkevich’s arguments: alleged unscientific nature of differentiated ap-proach to the concept of “document”, validity of pure theorizing regardless of practice, and denial of Paul Otlet’s methodology. The latter thought that there was the overdue need to develop the general theory of document similar to that in biology, sociology, physics and the so-called big sciences. The author demonstrates the wrongfulness of abandoning of the wider definition of the document by the International Standardization Organization (ISO). According to ISO, the document is an object that may be regarded as an element of documented quality management system. The practical effectvenesss of the method of rising from the abstract to the concrete which enables to narrow the concept of document down to the needs of individual libraries, is substantiated.