Aim to clarify the concept of social convention and the philosophical ideas associated with it as proposed by David Lewis and his contemporary critics, as well as to analyze the applicability of these ideas to the study of implicit rules of human behavior.
Material and methods. We analyzed the works of D. Lewis "Convention: A Philosophical Study", "Languages and Language", as well as the works of contemporary authors who critically start from the concept of convention by Lewis in their research: R.G. Millikan, V. Zachnk, M. Matczak, I.F. Deviatko, B. Skyrms, B. Celano and others.
Results. One of the main problems with understanding everyday behavior and speech as based on social convention by Lewis is the problem of determining the regularities of behavior. Lewis believes that conventions emerge from the preferences of some people based on the knowledge that others understand language and the world in general in the same way they do. But if each native speaker has in mind some own unique meaning, this does not prevent the appearance of an illusion of understanding, which in a sense leads to true understanding. It is the same for behavior: it is not very important how different participants of the interaction understand the rules of behavior, some result will still take place and everything will look as if the participants have assumed in advance according to what rules they themselves and their partners are going to act.
Conclusion. The idea of conventionality can be used to explain the grammar of behavior, if supplemented with the understanding that real natural signs are always "ill defined". A realistic theory of conventions should assume that signaling systems, languages, ideas about possible situations and behaviors coincide only partially among representatives of the population in which the convention is maintained, which does not prevent either communication or other coordinated behavior.