Confinement is permeates the plot as one of the central themes of Virginia Woolf's Mrs. Dalloway. It is a theme that applies not only to the eponymous main character and to the character of Septimus, but also to everyone in the story who has been touched by the changing times in which the novel takes place. Most of the mental confinement that is evident in the novel is partly due to the historical context of the story. The advent of WWI, its effects on the social psyche, and the role of each character within a dramatically changing world is what makes each of them behave in a way that denotes a constant state of meditation.
Mrs. Dalloway takes place in post WWI England. "The Great War" as it was called then, was something never experienced before in the social psyche; it would make the world "global" for the first time and, as a result, life as it was known then changed dramatically. The sudden exposure to the entire world expanded the economy hence placing the social class to which Clarissa belongs in danger of losing its status. The made the upper classes in England became more staunchly adhered to their own social rules.
Right in the middle of the rumble caused by social change, we find that, in a dramatic contrast, Clarissa Dalloway's world has never changed. As a middle-aged woman accustomed to "the beautiful life", she has gone through these trying times unscathed and somewhat clueless of what is going on outside her window.
...she always had the feeling that it was very, very dangerous to live even one day.
This is exactly where her confinement lays: in the lack of exposure to reality, Clarissa has remained confined to the limitations of her social class. As a result, she has also become confined to one form of thinking. This is perhaps the first time in which Clarissa wants to be "liberated".
She knew nothing; no language, no history; she scarcely read a book now, except memoirs in bed; and yet to her it was absolutely absorbing; all this; the cabs passing; and she would not say of Peter, she would not say of herself, I am this, I am that.
Confinement is even more evident in the character of Septimus who, in contrast to Clarissa has been directly and negatively affected by the changing times. A veteran of WWI suffering from shell-shock (PTSD), Septimus lives in a consistent state of trauma which is made worse by his doctor, who does not understand his situation. In his case, suicide was the only solution possible for his situation. Interestingly, his suicide brushed upon Clarissa (who never meets him) in a way that suggests that his physical death may represent the physical and mental liberation that Clarissa seeks.
Peter Walsh's own obsessive issues denote confinement of the mind. His inability to let go of his resentment, his highly judgemental behavior and even the way in which he presents himself describes someone who is limited by stubbornness to a point where his quality of life becomes equally limited.
Sally, as much as she criticized the social expectations of women, ends up as the very women that she once claimed to detest. Married and with five children, the now Lady Rosseter is far from the free-spirited, cigar-smoking teenager she once was. Although not directly characterized as unhappy, it is clear that Lady Rosseter ultimately is also confined to the boundaries that her class has learned to use to separate themselves from a changing world.