WOODY ALLEN and the meaning of life are like a sufferer from chronic indigestion and Christmas dinner. Allen simply cannot leave it alone, and yet it pains him.

At the end of one of his early films, Manhattan (1979), a despondent Allen lies on his bed recording into his dictating machine reasons for living, which include Louis Armstrong’s Hot Potato Blues. Things haven’t changed that much over the years, as Irrational Man (Cert. 12A) makes clear.

But nowadays the Allen character is played by somebody else. Here, without the Allen tics, it is Joaquin Phoenix, as Abe (short for Abraham or Abel?), a professor of philosophy newly arrived on Rhode Island. He sleepwalks his way through life. Nothing awakens him to life’s riches — not God, not love, not even Louis Armstrong, until (as you could guess) a pretty young woman crosses his radar.

Jill (Emma Stone) is an impressionable student with whom Abe forms a close friendship. Abe’s diet of Nietzsche and Kierkegaard has convinced him that, if God isn’t dead, then he’s certainly playing hide and seek with the universe. His head-talk with a fellow professor, Rita (Parker Posey), and her take on Dostoevsky don’t appear to get Abe any nearer an uplifting of spirits. Or do they? Before you know it, Abe is committing an existential act rather in the manner of Raskolnikov in Crime and Punishment. Murdering an evil man is the key to Abe’s happiness. To do is to be.

Allen has been here before with Match Point (2005), his modern-day version of the Dostoevsky classic, which was as turgid as his latest offering. Abe hasn’t really done his philosophy homework. Dostoyevsky (in Brothers Karamazov) doesn’t actually say that, if God does not exist, then everything is permitted. Quite the opposite. Without faith we cannot truly know right from wrong.

Murder as a solution to a meaningless, godless life is to be found in several other of the director’s films from Crimes and Misdemeanours (1989) to Cassandra’s Dream (2007), but usually they are funny as well as serious. Abe discovers moral purpose, but fails to find appropriate direction for it.

Allen’s alter ego is all too much in his head. If only Allen had read and believed Pascal’s words on the subject: “Take comfort, you would not be looking for me if you had not already found me.” But, there again, if he had, then maybe we wouldn’t have got all his marvellous films.