"This failure to recognize the true variety of historical source materials was his chief weakness as an historian. No one can read everything, but everyone should be consciously aware of all that exists waiting to be read. Whenever Butterfield turned to the technical tasks of the professional historian, a theme on which he spoke with firmness and sense, he talked only about letters and dispatches and gave no indication that he knew anything else to exist. History written on that basis cannot help but remain restricted and limited, and no major work of reconsideration, innovation or wider-ranging authority can be thus written except perhaps within the realm of that diplomatic history which Butterfield so rightly regarded as insufficient for a life's work."