The distinction between appearance and reality is one of the most important themes of the novel. No one in The Good Soldier is really who he seems to be, or who Dowell thinks him to be. Edward is not an honest, trustworthy "good soldier"; Florence is not a demure and faithful wife; and Leonora is not an upright, "normal" woman devoid of passion or emotion. The novel traces Dowell's realization that appearances are not reality, that the four are not really "good people."
Dowell's gradual realization, however, is trumped by the fact that the idea of "good people" seems to lose its very definition as the novel progresses. If this well-born and well-mannered English couple is not "good," and if his own wife is deceiving him, then he feels he has nothing to believe in. In the absence of appearances, Dowell is left only with madness, a skewed perception of reality. Ultimately, as the novel's first-person narration shows, personal perception is all one can ever have. "Reality" is merely one individual's version of the truth.
The Good Soldier constructs adultery as a destabilizing force in society. At its very core, it is a violation of the marriage contract, and the betrayal of a promise. But more deeply, adultery undermines the family structure on which the unity of the country is built. It can be both an act of power and of passion. Edward seeks the arms of another woman in order to escape Leonora's total control. Conversely, Leonora regains power by attempting to control even his adulterous liaisons.
The novel presents two kinds of adultery: the conservative type practiced by Rodney Bayham, and the passionate type led by Edward Ashburnham. Of the two, it is the passionate type that is dangerous, because such an affair leads to impracticality and instability. Edward's "abnormal" attachment to his mistresses, not sex, brings about the collapse of his marriage, and his eventual suicide.
In The Good Soldier, Dowell assumes faithfulness in marriage to be a very basic level of human morality. When faithfulness is questioned, all morality seems threated. Confused, Dowell wonders, "and if everything is so nebulous about a matter so elementary as the morals of sex, what is there to guide us in the more subtle morality of all other personal contacts, associations, and activities? Or all we meant to act on impulse alone? It is all a darkness."
Ford's novel defines and redefines normality. Dowell uses the term to assign people to categories: normal or abnormal, passionate or restrained, hero or villain. Such a system allows him to restore order to a morally chaotic world. He considers women like Leonora and men like Rodney Bayham to be "perfectly normal" individuals, content to live according to society's rules. Dowell associates "normality" with a lack of passion, and he uses the term in an increasingly condescending manner.