Cogitations, the last of the posthumous publications, is a collection of occasional writings representing Bion's attempts to clarify and evaluate both his own ideas and those of others by casting them in written form and frequently addressing them to an imaginary audience. Covering a period between February 1958 and April 1979, Cogitations delves into a wide range of material - psychoanalysis and science, mathematics and logic, literature and semantics. Some form a background to Bion's theoretical development, showing the doubts and arguments leading to the ideas expressed in his books, others highlighting and detailing some of the more abstract points in them, and some exploring topics destined for books that were to remain unwritten.