The paper is dedicated to the 50th anniversary of the edition of Berger and Luckmann’s The Social Construction of Reality. It was the occasion to convince about a real impact of this famous book, that was translated into Czech in 1999, on the thinking and the vocabulary of Slovak and Czech sociologists. But after initial interest in this book the sociological public gradually stopped at its formal recognition. However, even those sociologists who expressed interest in the theory of Berger and Luckmann, did not taken it as a theoretical whole, with own particular philosophical program. They are satisfied by choosing from social constructivism some original concepts, that as well as „symbolic universe“ must roofed their own account. It seems, that sociologists are afraid of social constructivism for its epistemological position, which is constant challenge to the realistic approach in sociology. However, these issues may be best resolved through discussions on philosophical and epistemological topics. We note three epistemological positions, each of which was a serious challenge to the idea of social construction. The first is the position of the classical epistemological realism. The second is the principle of philosophical apriorism, which is a prerequisite for any constructivism. The third position is presented by the theory of objectivation. This principle is a component of the social constructivism. We present each of these epistemological principles as one side of an imaginary triangle. The theory of social construction of reality is closed inside this triangle. This theory is the object of the philosophical influence of the three aforementioned teachings. They embody for it the pattern of philosophising, because they state the criteria of its philosophical competence. Therefore our proposed imaginary „epistemological triangle“ was used as a test tool for to ascertain the impact of various philosophical doctrines on ideological profile of social constructivism. The use of this triangle helped us to look deeper into the philosophical foundations of social constructivism and to verify their authenticity. It also helped us to dispel fears of social constructivism and of its allegedly excessive subjectivism.