Woody Allen of late is just too prolific, firing out film after film on an impressive yearly basis instead of maybe taking more time, sitting on the story, writing another draft.

The screenplays of the undercooked Magic in the Moonlight, Midnight In Paris, You Will Meet A Tall Dark Stranger et al felt like they needed another pass or two but with Irrational Man it has been the first time that it feels like Allen has filmed his notes such is the slight and underexplored material on show.

Allen fans will engage in mental gymnastics to convince themselves Irrational Man is a deep, philosophical treatise on ethics, morals, guilt and what have you – he is one of a small number of filmmakers willing to discuss murky themes like this - but the truth is this is the great man’s weakest outing for some time.

Joaquin Phoenix is Abe Douglas, the new philosophy professor at a prestigious college. He’s lost his zest for life: suffering from writer’s block and impotence, the surly Abe shuffles about campus sipping scotch from a hip flask. He’s cynical, burned-out, suicidal. Not even a come on from faculty member Parker Posey or proposition from infatuated student Emma Stone can inject some vitality into his existential existence. But when he overhears a conversation at the next table at his local diner, he finds a reason to live: a woman has lost a custody battle and believes it’s because her dastardly ex-husband’s lawyer is tight with the judge (Tom Kemp). It gives Abe an idea: if he kills the corrupt judge and the children are returned to the caring mother, surely a wrong will be righted. But it is murder.

We’re in Crimes and Misdemeanours territory here and it’s not easy to ignore the chasm in quality. There’s a lack of depth to Allen’s tragic hero: after spending twenty minutes of talking up nothing but the living legend that is Abe Douglas, and not one but two voiceovers (one from Phoenix, the other from Stone) doing a lot of the legwork, the professor, despite Phoenix’s best efforts, is not nearly as interesting as Allen thinks he is.

The scenes are short and irritatingly linked by a repetitive jazz score, making one unsure as to process the scene just gone or prepare for the one that’s about to unfold. There’s no spark to the dialogue, a series of philosophical debates (Kant, Kierkegaard, de Beauvoir, Sartre) and theories on who want to murder a judge and why and how. It’s nuts and bolts stuff that a writer finesses while circling the room, working through the ins and outs of a story. Notes on film.

The concern is that Allen’s slight latter work might overshadow the unforgettable genius earlier films. And a fan should be able to point to a work and honestly say it’s not up to snuff. This is not up to snuff.