Today, given the increase in the theoretical criticisms of positivistic approach, many scientists of social and human sciences emphasize on the qualitative methods of research instead of gathering quantitative data and statistical analyses. One of the widespread methods of qualitative research is critical discourse analysis. Philosophically, critical discourse analysis based on structuralism reduces reality into human structures by emphasising on human agency. Referring to the logical requirements of structuralist foundations of critical discourse analysis, the present paper concludes that epistemologically this approach leads to relativism, sophistry and negation of cognition, axiological relativity, self-contradiction, refusal of truth and falsity, and refusal of ethics.