Philosopher and writer Kwame Anthony Appiah, who chaired the judges, said all six finalists were "miracles of stylistic invention."
"In each of them the language takes centre stage," Appiah said.
"Each one explores the anatomy of pain - among the incarcerated and on a slave plantation, in a society fractured by sectarian violence, and even in the natural world," he said. "But there are also, in each of them, moments of hope."
The first graphic novel to be longlisted, the dystopian "Sabrina" by US author Nick Drnaso, also failed to make the final six.
But the inclusion of Scottish poet and writer Robin Robertson's "The Long Take," which combines verse with photographs, means there is still a place for innovative graphic form in the shortlist.
One of the new favourites is another Irish author, Anna Burns, whose "Milkman" portrays an isolated young woman navigating life in the shadow of paramilitary violence in Northern Ireland.
The Irish Times commented that Rooney's exclusion was "the biggest surprise" in the shortlist.
US writer George Saunders won last year's prize for his novel "Lincoln in the Bardo," which portrays 19th-century US president Abraham Lincoln grieving his dead son.
The winner of the 2018 prize will be announced on October 16.
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"In each of them the language takes centre stage," Appiah said.
"Each one explores the anatomy of pain - among the incarcerated and on a slave plantation, in a society fractured by sectarian violence, and even in the natural world," he said. "But there are also, in each of them, moments of hope."
The first graphic novel to be longlisted, the dystopian "Sabrina" by US author Nick Drnaso, also failed to make the final six.
But the inclusion of Scottish poet and writer Robin Robertson's "The Long Take," which combines verse with photographs, means there is still a place for innovative graphic form in the shortlist.
One of the new favourites is another Irish author, Anna Burns, whose "Milkman" portrays an isolated young woman navigating life in the shadow of paramilitary violence in Northern Ireland.
The Irish Times commented that Rooney's exclusion was "the biggest surprise" in the shortlist.
US writer George Saunders won last year's prize for his novel "Lincoln in the Bardo," which portrays 19th-century US president Abraham Lincoln grieving his dead son.
The winner of the 2018 prize will be announced on October 16.
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