Kurt Vonnegut has always been funny. His novels have been saved from bleak, fatalistic despair by his hare-brained sense of humour and his hope that humanity can redeem itself. Slaughterhouse-Five, for instance, is a comic novel about the bombing of Dresden in which the horrors that Vonnegut himself witnessed are alleviated by clownish characters, aliens and time warps. In Cat's Cradle, the intellectual nihilism of Bokononism, an invented religion "based on lies", never seems as depressing as it should, mainly because the book is so funny. It's hard to imagine what Vonnegut would sound like without a sense of humour.

Yet in his latest book, a collection of jottings about contemporary America, Vonnegut explicitly worries that he is no longer funny. What prompts this fear is the low state into which his country has sunk. "I know of very few people who are dreaming of a world for their grandchildren," he writes, adding that this is probably why he has lost his sense of humour. He recalls Depression-era America, when the idea of future prosperity gave people hope despite the bleakness of their situation. And he can find no modern equivalent.

However, in a twist that is typical of Vonnegut, A Man Without a Country turns out to be hilarious. For example, he says he is going to sue Brown & Williamson Tobacco Corporation for printing unfulfilled promises of death on his cigarette packets: "Thanks a lot, you dirty rats. The last thing I ever wanted was to be alive when the three most powerful people on the whole planet would be named Bush, Dick and Colon." And he has not lost his talent for making aphorisms work through humour: "How beautiful it is to get up and go out and do something. We are here on earth to fart around. Don't let anybody tell you different."

I expected Vonnegut's voice to be more straightforward in this book than in his novels, stripped as it is of fantastical plot schemes and comic fall-guy characters. But all the old contradictions are here. He despairs not just of current political leaders, but of an entire generation he regards as uncaring. Yet he then makes brilliant jokes and offers glimmers of optimism. For instance, he praises the librarians who refused to hand over lending records to "anti-democratic bullies", adding: "So the America I love still exists."

I expect that if Vonnegut were more consistent, the charm of his unique, confused and confusing voice would be lost. He is in his eighties now, still writing with verve despite his earlier promise never to write another book, and despite his bleak view of modern life. I hope he's not too depressed to write again.