The bohemian life does not change much. In Dublin’s boho world, drifters, druggies and assorted parasites congregate in smoky pubs. Struggling artists, alcoholics and slumming students, they live in a world of their own. The mixture of backbiting gossip and boozy philosophy is timeless. It has echoes of the Parisian Left Bank or Dublin in the 1950s.

Sean O’Reilly’s second novel, The Swing of Things, is set in Dublin’s bohemian world. The protagonist, Boyle, is a former IRA prisoner who has moved from Londonderry and is studying philosophy at Trinity College. His life of quasi-intellectual angst and drunken violence recalls the work of earlier writers such as JP Donleavy and Alexander Trocchi, who described a similar milieu 50 years ago.

But look closer. This is Dublin on the cusp of the 21st century. The city is littered with lap-dancing clubs and a new immigrant underclass of Russians and Nigerians inhabiting the seedy bedsits. The drugs are harder and more pervasive. Despair and alienation run deeper. Boyle’s problems are rooted in his republican past: his attempt to find his real self in existential philosophy is futile.

There are echoes of a previous generation of writers. Boyle reads Jean-Paul Sartre: he is revolted by the texture of everyday life, like the hero of Sartre’s Nausea. At times, O’Reilly’s prose matches the gallows humour of early Samuel Beckett. Donleavy and Trocchi, those Celtic existentialists first published in 1950s Paris, also wrote about violent men who justify their acts with philosophy.

Donleavy’s novel The Ginger Man is set in a brawling, drunken Dublin, with an egocentric antihero who specialises in violence towards women. Trocchi’s first novel, Young Adam (recently filmed with Ewan McGregor), features a lone male with a clinical fascination in a woman’s death.

Like Young Adam, O’Reilly’s novel begins with a drowning. Boyle, brooding in his bedsit, becomes obsessed with newspaper images of a woman whose body is found in the Liffey. As we gradually learn about his past and his propensity for violence, we begin to suspect he is not telling us the whole truth, and that his pedantic quest to find the right words masks a greater denial. The echoes of the jaded post-war existentialism of Trocchi and Donleavy ring loudly.

But O’Reilly was born in Derry in 1969, when the ferment of the Parisian Left Bank had faded and a different, more violent revolution was beginning in Northern Ireland. The Swing of Things links existentialism and armed struggle.

O’Reilly echoes the themes of those 1950s bohemians, but he comes to a different conclusion. Although his protagonist believes that his inner void is a great philosophical conundrum, it is ultimately rooted in the Troubles.

The original existentialists focused on the self. The aftermath of the second world war led them to believe that, morally, anything was possible. The ordinary rules no longer applied: consensual society was something to be despised and subverted. Trocchi’s Adam feels alone, cut adrift from normal society and morality. He regards himself as a deep thinker — a Nietzschean superman — and believes this grants him a dispensation from the ethics of the common herd. Similarly, The Ginger Man is a swaggering brute, casually abusive to women. Male ego is everything: any kind of excess is justified on the grounds of its supposed authenticity. These pub philosophers rationalise their own amorality by linking it to some greater nihilistic void.

But O’Reilly writes in and about our own era. The boozy subculture remains, but it is no longer easy for Boyle to justify his actions. He hopes reading Sartre will somehow render him real to himself. He gets drawn into a world of drifters, violent alcoholics and street poets. He envies their devil-may-care attitude, but he thinks too much, and tries to resolve it by thinking even more.

Much of the novel is seen from Boyle’s perspective. Nouns and adjectives stutter and loop as he tries to pin down in words everything that happens to him. He feels utterly alienated. He does not fit in at home and his efforts to create a new life are clumsy and paranoid. Like Sartre in Nausea, he is an unstable observer horrified by what he sees.

But O’Reilly also offers other points of view. We dip into the frantic, free-wheeling mania of the people Boyle meets on the street. We learn that his fellow prisoners had nicknamed him Buddha: to them, his attempt to be a deep thinker is a risible affectation.

It seems he has ideas above his station: that he fails to understand the gulf between a working-class former prisoner and the world of middle-class college students. His quest for authenticity is perceived as a betrayal of his roots.