The great and golden rule of art as well as of life, wrote William Blake, is that the more distinct, sharp and defined the boundary line, the more perfect is the work of art; and the less keen and sharp the greater is the evidence of weak imitation, plagiarism and bungling. 'Great inventors in all ages knew this - Michael Angelo and Albert Durer are known by this and by this alone'; and another time he wrote, with all the simple directness of nineteenth-century prose, 'to generalise is to be an idiot.