The idea of madness is central to Regeneration. At its simplest level, madness is the problem that plagues the soldiers at Craiglockhart War Hospital, the problem that the psychiatrists long to "heal." The symptoms of madness range from an irrational fear of blood to mutism, from an inability to eat to a vocal protest of the war. In short, madness translates into an inability to act in a manner that normal society considers rational. These "mad" men live outside the bounds of what is socially acceptable, and are therefore removed from their duty, labeled as "shell-shocked," and hidden away in a war hospital in Scotland. For many of the men, such treatment only further exacerbates their problems, leaving them feeling shamed and emasculated over their breakdown.
A deeper level, however, the question of madness is one that Barker leaves unanswered. The most important "regeneration" in the novel is the fact that Rivers begins to question the very nature of madness; as a character, he grows into a new type of person, one who challenges the assumptions of his society. He begins to wonder whether it truly was madness for these men to break down in the face of such horror and death, or whether it was madness that so many men (including Rivers himself) blindly followed a program of war and decimation in the first place. Rivers begins to wonder if he himself is mad for "healing" patients only to send them back to war to be killed. The novel provides no easy answer, but instead provokes further thought about the question of madness and the nature of sanity.
Love and intimate friendship between men is a continual theme in the novel, as all of the soldiers and doctors in the novel are male. On the battlefield, love between men is an accepted and desirable occurrence. Sassoon is complemented on the love and dedication he demonstrates for the men who serve in his division. Such a relationship involves a level of caring and comradeship for fellow soldiers. Society looks upon such love favorably, as it engenders a better army.
However, there are bounds to the acceptable societal level of male emotional interaction in Regeneration. In Chapter 17, Rivers mentions these limits. He tells Sassoon that although comradeship is encouraged, "at the same time there's always this little niggle of anxiety. Is it the right kind of love?" Homosexuality is an implied, but not overt theme in the novel. Rivers suggests that in wartime, the reaction to homosexuality would only be more intolerant than in peacetime, as the authorities would want to make it clear that there are penalties for the wrong kind of love. From this perspective, love between men—and male emotional relationships more generally—are a smaller part of a larger goal of curbing what is deemed socially unacceptable behavior. Homosexuals, like shell-shock victims, are outside the boundaries of normal social interaction. This being the case, Sassoon's homosexuality is an underlying threat to the stability of the social order. Through his sexual preference, he challenges the control of the state exerted in wartime, and his character emerges as a more complicated and controversial figure.
Parenthood is linked in the novel to comradeship and caring. Parent-like protectiveness appears as a natural reaction to having men under one's command or patients under one's watch. Especially in wartime situations—in which control over many aspects of one's existence is so limited—a desire to protect others serves as an outlet for the need for some measure of control. Some examples in the novel are Prior's fatherly feelings for his troops, and the way many of the patients hold Rivers to be a surrogate father figure.
In Regeneration, the idea of parenthood is complicated by unorthodox gendering of protective roles. A former patient of Rivers's refers to him as a "male mother." This comparison distresses Rivers: "He distrusted the implication that nurturing, even when done by a man, remains female, as if the ability were in some way borrowed, or even stolen, from women. If that were true, then there was really very little hope." Here, it becomes clear that fatherhood and motherhood tie into a larger issue of gender roles in society. Rivers's method of treatment requires an expression of emotions, a traditionally female idea. Yet although Rivers resents that nurturing is considered to be a uniquely female trait, he ultimately accepts the idea that he acts in a fatherly and motherly way to his patients. For in the end, good parenthood involves care for the individual. Although war rejects such attention to the individual, as a doctor, Rivers makes his best effort to provide it.