The book discusses the taxonomic continuum, the relationship of the empirical sample of species and their characters with a wider biologically possible combination of them, as well as the structure of the taxon. The author believes that the taxonomic continuum is fundamentally impossible and that the structure of the taxon is inherited from the ancestor species, and the empirical sampling of the facts of systematics is always random in relation to their totality. This confirms the admissibility of distinguishing taxa, their reality as biological organizations and justifies the probabilistic nature of taxonomic knowledge. The paper shows the possibility of predicting signs of still unknown and potentially feasible during the further evolution of taxa based on the theory of classical systematics.