Kazimierz Ajdukiewicz understands skepticism as the thesis that there is no criterion of truth and that the justification of any thesis is impossible. According to Ajdukiewicz, a typical skeptic confuses two levels of justification: the first order justification of a proposition s and the second order justification of the proposition that s is justified. However, the first-order justification is possible without second-order justification. This argument presented by Ajdukiewicz in 1923 heralded the epistemic externalism concerning justification developed by Alvin Goldman in (...) 1980 and the externalist response to skepticism developed by F. Dretske and M. Williams. They all suggested weakening the traditional concept of justification and concluded that if we accept the possibility of justification without self-justification, the skeptical regress is blocked. However, such a response to skepticism is dependent on the externalist notion of justification. Ajdukiewicz had opportunity to use the stronger argument from self-refutation, but he underestimated its utility. The other side of Ajdukiewicz’s relation to skepticism is his radical conventionalism that presupposes some moderate form of skepticism in a broad sense. The article is an attempt to determine what kind of skepticism Ajdukiewicz accepted and what kind he rejected. The conclusion is that Ajdukiewicz is an anti-skeptical fallibilist. (shrink)