As we know, there are three characters in this story - the nameless narrator, Roderick and Madeline Usher. Roderick and Madeline who live in the mansion are the remaining members of the time-honored Usher race. Both of them had very serious illness. Roderick believed the house somehow controls his behavior and what will finally happen to him. And his sister, Madeline's disease caused her to lose consciousness and feeling. According to "I learned that the deceased and himself had been twins, and that sympathies of scarcely intelligible nature had always existed between them," (The Fall of the House of Usher. The Heath Anthology of American Literature. P1391) we know they are twins and it seems that they are so close that they can sense what is happening to each other. I also consider that they two also represent the mental and physical components of a unitary being or soul.
The house had a very strong connection with Roderick and Madeline Usher. I think that the author, Poe uses "House of Usher" to refer to both the decaying physical structure and the last of the "time-honored Usher race." Besides, "the echo (but a stifled and dull one certainly) of the very cracking and ripping sound which Sir Launcelot had so particularly described. It was, beyond doubt, the coincidence alone which had arrested my attention; the sound, in itself, had nothing, surely, which should have interested or disturbed me." (The Fall of the House of Usher. The Heath Anthology of American Literature. P1393) shows that the crack in the Usher's mansion symbolically suggests a fissure or split in the twin personality of Roderick and Madeline, and also forecast the final downfall of both family and mansion; according to Edward H. Davidson, the crack represents "an irreconcilable fracture in the individual's personality." .
The house itself was described as having a "specious totality" (The Fall of the House of Usher.
