In his article "On the Foundation of Knowledge" Schlick regards the quest for certainty in human knowledge as the fundamental problem in epistemology.¹ This leads him to attempt to refute the view of O. Neurath and R. Carnap² that their so-called protocol propositions provide the foundations of empirical knowledge and instead to propose his own Konstatierungen or affirmations as basic to science. It was, in fact, his opinion that all fundamental propositions, whether called "protocol" or "basic" propositions reduce in the end to hypotheses and as such are always infested with uncertainty: affirmations alone are synthetic propositions without being hypotheses and possess the characteristic of absolute certainty.