One interpretation of “The Fall of the House of Usher” is that it presents a dramatized interpretation of a split-personality disorder. At the least, the tale explores different aspects of identity and the ways in which those aspects might be fractioned or made distinct. Differences between the physical and the mental parts of the self are emphasized and explored in the text, as well as the way that parts of the self interact.
Roderick and Madeline are one person split into two pieces.
Roderick has no identity without Madeline.