Peter Walsh is historically grounded, but negatively. He is absent from England during the years 1918 to 1923, the years directly following the war, so that he can then comment on the starkness of the change otherwise invisible (or merely impressionistic) to those who have lived through the post-war years.
The world in which the Dalloways live and move–the “governing class” ganged in various Imperial projects–is under threat. It is a decadent rather than crescent class. This decadence undercuts the sense that World War I marked some sort of triumph of British civilization: that the death of thousands of men is compensated for by a strong Britain. In the short story from which Dalloway was draw, Clarissa says: “Thousands of a young men died so that things might go on.” But this shows Clarissa to be out of step with her time: thinking that things are still going on dramatizes her ignorance. She is living in the past.
Part of this “past” depends not he illusion that the ruling class is not conditioned on what Forster calls “islands of money.” Dinner parties are a “grand deception,” in which food is mysteriously unpaid: “life appears musical” to this class, because they are not bitten by the realm of necessity. There’s is the realm of the Wilcoxes.
Septimus is a threat, excluded from Clarissa’s “party” because he refuses to forget a war that everyone is struggling to put behind them. This is part of a larger cultural forgetting that includes turning away from the economic base, one could argue. But it is also because he is uncontrollably, intensely passionate–a challenge to the governing class’s stoicism. The same with Peter Walsh. Though his early socialism is hollowed out and he has become part of the system that he has convinced himself that he is no longer a part of, his passion for Clarissa remains.
The novel dramatizes the absorption of these energies. In this way, Woolf attempts to “criticize the social system, and to show it at work, at its most intense.” Perhaps there is also a contribution to changing it, however slight.