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.
The idea of "regeneration" functions in the novel to inform and develop the concepts of healing, changing, and regrowth. It occurs several times, most notably in the nerve regeneration experiments Rivers practices on Head, and in the figurative regeneration of men's "nerves" in the War Hospital. Rivers also undergoes a sort of regeneration in the novel. Through observations of his patients, reflections on his upbringing, and most importantly his interactions with Sassoon, Rivers questions many of the assumptions of war and duty that he previously held. This motif highlights the comparison between mental and physical healing, and it emphasizes the regrowth and change in a man who has been confronted with the reality of war.
Emasculation appears in the novel in a wide variety of forms. Sassoon remembers the young boy in the bed next to him who has been castrated on the battlefield. Anderson dreams he is tied up with corsets. Prior recalls his weakness against his father and the influence of his mother. Sassoon mentions to Rivers the topic of homosexuality and the idea of an "intermediate sex." Rivers reflects on the "feminine" nature of healing and caring for one another on the battlefield.
Emasculation signals the powerlessness that soldiers feel when confronted with the shocking reality of war. Although they try to do the manly thing by enlisting in the war and fighting for their country, they must face society's judgment that it is decidedly unmanly to suffer a breakdown. In the hospital, Rivers's method of treatment involves more ostensibly unmanly actions, as the patients are forced to release their emotions and discuss their feelings. Willard is so opposed to the unmanliness of his condition that he refuses to believe he has anything other than a physical problem. Yet, Rivers achieves results in a sympathetic manner; he helps his patients to improve and lead a normal life once again. Through further "emasculation" the patients are able to improve. Ultimately, Barker's exploration of emasculation in the novel challenges traditional notions of manliness.
In Regeneration, mutism functions as a symbolic manifestation of the disempowerment and helplessness the men feel. Both Prior and Callan are affected by mutism after extremely horrifying incidents. Rivers reasons that mutism might be caused by an inability to voice dissent or express opinion over any part of one's own life. He notes that mutism occurs most often among regular soldiers, not officers—men who are entirely at the mercy of their commanders. Mutism, however, is in itself an assertion of power. Through silence, these men are disobeying those who have power over them. How Rivers and Yealland differently handle mutism is a reflection on their own need to reinforce control over their patients.
Trenches are symbolic in the novel, much as they are in the poetry of the Great War. The trenches are likened, both literally and figuratively, to graves. Many of the patients have terrible experiences and memories involving trenches. Prior, most notably, remembers waking up in a trench one morning, only to turn around and find two of his men killed by an exploded shell. The trench became the men's grave, as Prior was forced to mix their remains with lyme and use them to reinforce the walls of the trench.