In works of Eleanor Rosch “natural” concepts was introduced that reflect a high correlated structure of features of objects of the external world. Prototypes of the “natural” concepts are clearest cases of objects that reflect this highly correlated structure. The same high correlated structure manifested in the “natural” phenotypical classification. To formalize this highly correlated structure, we define a special type of probabilistic causal relations and then probabilistic formal concepts as a cyclically connected probabilistic causal relations. Based on these definitions, we developed a method of prototypes discovery and illustrate it on the example of digits’ prototypes discovery.