The article is dedicated to the word "durak" (a fool) functioning analysis in Dostoyevsky's texts, for whom this word is one of idioglossas (key‐words, which characterize the author's idiostyle). The analysis is based on the system of lexicographical parameters, such as the word's usage in idiomatic constructions, word's collocations, associations and so on. The results of the analysis allow to come to some conclusions about the motives of why this or that person is considered as "durak" in Dostoyevsky's discourse.