Lacan is an influential figure of 20th Century thought. Being a psychoanalyst, a linguist and at the same time a philosopher, in his theory he combines all three of these disciplines. Even in his later works, he tried to combine his theory with mathematical formalization. His theory influenced three important political thinkers: Laclau, &amp / #381 / i&amp / #382 / ek and Badiou. The purpose of this dissertation is mainly to examine Lacan&rsquo / s thought and its impasses which could be found especially in the political applications of his theory. First I start with a critical reading of Lacan&rsquo / s own works. I try to figure out the idealizations, presuppositions and blind spots hidden in his work. I develop my critical reading by focusing on the works of Laclau, &amp / #381 / i&amp / #382 / ek and Badiou. The main argument of this dissertation is, such a critical reading of these philosophers will lead us to a general questioning of Lacan&rsquo / s theory and the legitimacy of its applications. Lacan&rsquo / s use of the impossibility as a founding principle and his passion for formalization cause several idealizations, like the idealization of the neutrality of the signifier, the idealization of the non-represented and so on. These problems are extended and transformed into other ones in his disciples&rsquo / works. For Laclau, the problem is transformed into a purely content-free understanding of elements of democracy which ends up with paradoxical results. For &amp / #381 / i&amp / #382 / ek and Badiou, because of their insistence on a political theory based on the impossible real, their subversive theories end up with a theory which take the form of messianic discourses. What I propose is a reconsideration of the role of the theory on the understanding of human reality: in principle every theory excludes some portions of the richness of human life-world, therefore every theory must have a retrospective and critical stance against its own founding principles. This cannot be done by formalized theories which keep the formal structure of itself untouchable.