In all the diversity and manifold researches of inference its nature remains unrevealed, as there is a lack of the uniform basis of the inference occurrences. It is mainly connected with the non-homogeneity of the inference action and a huge spectrum of its occurrence in language and speech. The study focuses on the search for the universal and relative to the nature of inference criteria of the classification of inferences in language and speech to penetrate deep into the essence of the discussed phenomenon. In this regard, the paper presents an analysis and discussion of the existing inference classifications on the basis of such criteria as functionality, a vector of action, a level of cognitive procession, inferential relations, etc. The aim of the analysis is to compare the current classifications of inferences, to make a conclusion about possible vectors of the inference actions in language and speech and to find out the universal, cognitive foundation underlying inference occurrences. Taking into account the nature of inference as a way of human thinking, the types of inferences are identified according to such mental operations as comparison, filling in (framing), integration, elimination, deduction, induction on the material of various linguistic resources (texts, utterances, dialogues). The proposed classification requires further consideration on the basis of a broader linguistic material (various types of discourse, utterances involving polysemantic words or phraseological units; the study of nomination processes of complex linguistic units like idioms, derived verbs, compound nouns) and can be modified and complemented.