Ever since philosophy became conscious of itself, there has been a problem of the relations between the real world which philosophy sought to understand and explain, and the thought by which it sought to explain it. It was found that thought had certain requirements and conditions of its own. If the real world was to be understood through thought, there was a question whether thought and the real correspond ed in all respects, and therefore whether they had the same conditions and laws, or whether some of these were peculiar to thought alone. For the solution of this problem it was necessary...