Percy Bysshe Shelley, like Edmund Blake, has a reputation as a difficult poet: erudite, imagistically complex, full of classical and mythological allusions. Shelley possessed two remarkable qualities of intellect — a brilliant imagination and a logical exactness of reason. Mary Shelley’s comment clearly challenges the idea of system by asserting that a central dualism runs through Shelley’s work: on one side is the brilliance of imagination, on the other the logical exactness of reason. The concept of the ‘poetical’ is interesting: from what Shelley says, one could fairly suppose that Satan might be considered the more appropriate hero if the criteria were to be complexity of character, vicarious excitement or intensity of conflict. Shelley’s conception of the process of change is wildly simplistic, and it would also be possible to criticise the passage, and many others like it in ‘Prometheus Unbound’, as a mere catalogue.