The article offers the thesis that moral theories and practice should satisfy the minimal logical requirement of consistency. Since logic is often considered the main criterion of rationality, the theoretical foundations of various interpretations of ethics can be considered rational in this respect.
In his theory of natural laws David Lewis rejects the authenticity of impossible worlds on the grounds that the contradiction contained within his modifier "in (the world) w" is tantamount to a contradiction in the whole theory, which seems unacceptable. At the same time, in philosophical discourse very often researchers use counterfactual situations and thought experiments with impossible events and objects. There is a need to apply the theory of worlds to genuine, concrete, but impossible worlds.
The theory of argumentation is supposed to be connected to rationality. Traditionally, rationality was defined in terms of logic, and at the same time considered as an essential part of the theory of argumentation. Thus argumentation acquired the property of rationality, while the rhetorical component ensured the success of communication. However, the possibilities of different logics and the existence of practical rationality assume a different order of categories by their generality: rationality, argumentation, logic.
The concept of analyticity plays an important role in establishing truths. Both in the traditional logic of terms and modern logic of predicates, similar approaches are used to reconstruct the idea of reliable substantiation. Kant used the categories of synthetic a priori, Frege relied on the features of terms (individual constants and functions) to formulate the conditions for the application of definitions.