King Lear Sub-plot

The relationship between Gloucester and his two sons, Edgar and Edmund, can be viewed as a sub-plot that can be compared and contrasted to that Lear and his daughters.  Just as Lear turns away his true faithful daughter, Cordelia, Gloucester turns away from his honest son Edgar to the manipulative and greedy son, Edmund.  Both fathers make the same error in judgement by listening to the lies of their manipulative children, while turning away their faithful children in an unjustly manor. 

Gloucester also suffers from his error, but in a much more physically painful sense.  Edmund's betrayal of his father results in Gloucester's eyes being gouged out, while Regan and Goneril's mistreatment of Lear results in his slip into senility.  The suffering in both these senses is ironic in effect: Gloucester was blind of both Edgar and Edmund's true intent just as Lear was mad to believe Regan and Goneril's greed for love.  It is only when both of the fathers have physically succumbed to their individual faults that they see the error in their ways.

Shakespeare makes an interesting parallel with the sub-plot of this play, but it fails to help the overall plot and understanding.  Both father's made a mistake, mistrusting the wrong of their youth, and both suffer and ultimately see their mistake through their pain.  The only difference is the method by which each was punished in the end, which ultimately does nothing for the story; it just creates two of the same tragic protagonists.  Perhaps if one father would have caught the slip or possibly further punished himself, there would be more contrast between each one's plot to help advance the plot of the overall play.