Editor's note.--The nature of the axiom of reducibility.--A logical analysis of the concept of probability.--The concept of identity.--Moritz Schlick's significance for philosophy.--Hypotheses.--Is logic a deductive theory.--The relevance of psychology to logic.--What is logical analysis?--Fiction.--A note on existence.--A remark on experience.--The linguistic technique.--Belief and knowledge.--Two accounts of knowing.