 However, while Cohen’s interests and views evolved over the course of his career, his philosophy from all three periods nevertheless exhibits points of deep continuity. All of Cohen’s major works share a profoundly historical orientation. A concern with the history of philosophy dominates his writing, and he was convinced of history’s continuing significance for philosophy in the present. But he was also concerned with the histories of those subjects he took to be philosophy’s topics, including science, ethics, and religion. This concern for history permeates his thought so completely that even in his systematic works, he prefers to introduce concepts and theories not by defining them straightforwardly, but by rehearsing major episodes in the history of their development. This historically-oriented method was a model for what later philosophers called Problemgeschichte – that is, the history of the origin, development, and evolution of philosophical problems. In stands in contrast to historical surveys of candidate solutions to problems the philosopher conceives as fixed, unchanging, and unresponsive to a broader philosophical context. (In Cohen’s hands, this historical orientation contributes in no small part to other aspects of his writing that none of his readers can fail to notice: its obscurity, repetition, and sometimes unnecessary length.)