What beliefs about the "sentience" of matter does Usher express to the narrator in The Fall of the House of Usher?
Roderick Usher's observation of "the sentience of all vegetable things" extends to his conviction that even inorganic things, such as the stones of his mansion, take on a certain consciousness of their environment and those who dwell within.
Usher is convinced that non-living things of the natural world, as well as the living things, have "molded the destinies of his family" and made him what he is. While the narrator declares that he will make no comment on this opinion, the idea of pathetic fallacy enters the narrative at this point. Usher believes the arrangement of the stones, the fungi growing on the stones, and the decaying trees that surround the house have had a longstanding effect upon the destinies of the Usher family; furthermore, they have even affected the formation of his own being.
In this part of his narrative, Poe seems to extend the concept of the influence of one's environment as one that has not just a psychological effect, but also exerts a physical one. That is, Roderick believes the outward decay and conditions have affected the lives of the Ushers. Interestingly, ancient peoples attributed the ravages of fungi to the wrath of the gods, so they, too, felt an influence upon their lives by such growth.
"Sentience" is a term used to describe having feelings or emotions. While plants are alive, they are not believed to have feelings. While animals seem to have reasoning skills, they are also not necessarily believed to have feelings.
Roderick Usher believed that all things that were "alive" were sentient beings, from mushrooms to mold to trees and more. He says that some of these inanimate objects around him have shown this in the way they have begun to take on "an atmosphere of their own," mostly the water of the lake and the walls of the House of Usher. He tells the narrator that these things have influenced the many generations of his family, forming his destiny and therefore making him into who he is today.