By Conrad Schumaker (American Literature: A Journal of Literature. Vol. 57 (Dec. 1985): 588-99.)
For John, mental illness is the inevitable result of using one's imagination, the creation of an attractive "fancy" which the mind then fails to distinguish from reality. He fears that because of her imaginative "temperament" she will create the fiction that she is mad and come to accept it despite the evidence—color, weight, appetite—that she is well. Imagination and art are subversive because they threaten to undermine his materialistic universe.
Ironically, despite his abhorrence of faith and superstition, John fails because of his own dogmatic faith in materialism and empiracism, a faith which will not allow him to consider the possibility that his wife's imagination could be a postive force. . . John's role as a doctor and an American male requires that he use his "knowledge" continuously and doggedly, and he would abhor the appearance of imagination in his own mind even more vehemently than in his wife's.