On the other hand, Ixion never appears in classic lore as a hero. He has been called the "Cain" of Greece, because he was the first, as Pindar says, "to introduce to mortal men the murder of kin not unaccompanied by cunning." Zeus appears, however, to have shown more leniency to him for the crime of killing his father-in-law than he ever did to Prometheus, as he not only purified him from murder, but invited him to a seat among the gods. But to quote Pindar again, "he found his prosperity too great to bear, when with infatuate mind he became enamored of Hera.... Thus his conceit drave him to an act of enormous folly, but the man soon suffered his deserts, and received an exquisite torture." Ixion, then, in direct contrast to Prometheus, stands forth an embodiment of the most detestable of sins, perpetrated simply for personal ends. To depict such a man as this in an attitude of defiance, and yet to justify his defiance, is a far more difficult problem than to justify the already admired heroism of Prometheus. It is entirely characteristic of Browning that he should choose perhaps the most unprincipled character in the whole range of Greek mythology as his hero. He is not content, like Emerson, with simply telling us that "in the mud and scum of things there alway, alway something sings"; his aim is ever to bring us face to face with reality, and to open our ears that we may hear for ourselves this universal song. In fine, Browning chose Ixion and not another, because he wanted above all things an unquestioned sinner; and the task he set himself was to show the use of sin and at the same time exonerate the sinner from the eternal consequences of his act. So mystical is the language of the poem that it is extremely difficult to trace behind it the subtle reasoning. Mr. Nettleship has given by far the best exposition of the poem, though even he does not seize all its suggestiveness.