“Happy Birthday, Noam Chomsky, Happy Birthday to you!” – Perhaps in your family it’s not humanist philosopher Noam Chomsky who gets his own day, but every right-thinking family surely takes time to celebrate the life of a radical thinker each year – right?

Set your absurdity and exaggeration filters up right to the top, and you will be ready for the strange, raw experience of Matt Ross’s Captain Fantastic.

Viggo Mortensen plays Ben Cash, a middle-aged father of six who decided ten years ago along with his wife, Leslie (Trin Miller), that society was falling apart, and the only truly rational way to raise children was to take them out into the woods and live life off the grid. We meet the family in full self-sufficient flow, killing deer for lunch, keeping fit with cross-country aerobics, climbing sheer rock faces for fun and, of course, relaxing around the fire with philosophical and literary classics – and maybe a spontaneously composed song or two.

The children seem to love their existence, and have the depth of thought and insight any parent would proudly declare to other parents at dinner parties. The only fly in the ointment is the long-term absence of their mother, who is nowhere to be seen as the film begins.

We discover that Leslie is suffering from a chronic illness, spending a lot of time recovering at a local hospital. Ben sets out in their adapted family school bus/shelter ‘Steve’ for news on her progress, and the film is set in motion: is the Cash family’s apparently idyllic isolation about to end?

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Captain Fantastic is a very unusual movie in its ability to divide audiences for the best of reasons: what is it trying to say? And that’s not the “this movie makes no sense” kind. I was struck by the incredible balance present in the narrative, script and catalogue of exceptional performances.

Different approaches to parenting, love, commitment, health, truth and life in general all come to the fore in subtle and believable ways as Ben is forced to confront family, friends and the wider world; and to my eyes and ears, Matt Ross & co. were not attempting to present any kind of answer to these questions, but instead gently persuading the audience to consider their own preconceptions and values.

It is remarkably non-confrontational given the weight of its subjects. Be prepared to delve into thorny issues such as mental illness, custody, abuse and moral objectivity – but also be ready to laugh! The extremes of Ben’s family come across more like a satirical cartoon than an idealised suggestion, allowing Ross to bring out the natural humour present in confusing culture-clashes where the ‘right’ answer doesn’t jump out at you.

A scene where Ben takes the family to his sister’s house for dinner & a sleepover manages to cover a huge range of tones & ideas, evolving through awkwardness, farce & uncertainty with consummate deftness – and very much bolstered by superbly nuanced performances from Steve Zahn & Kathryn Hahn, more commonly known for Adam Sandler movies & raunchy comedies, respectively.

Viggo Mortensen is superb in the lead role, but more for his ability to disappear into the movie, allowing the viewer to consider his character’s views & behaviour as if they are genuinely authentic. He imbues Ben with equal parts warmth and frustration, so you can’t help but flip flap around whether you really sympathise with him or not. The six children, all with TV or movie acting credits to their name, are also wonderful to watch, managing to convince you they are more than caricatures – and a special note must go to George MacKay, whose painfully evident passion and turmoil throws much of the movie’s ideas into sharp relief.

It will not be everyone’s cup of tea, especially as the film’s moral & philosophical musings could be received as a little ‘preachy’ – but I feel this does a disservice to the movie. I really don’t believe it wants to present any of the characters or families in a purely positive or negative light, or specifically challenge generally accepted norms – if anything, it wants you to step back and ask what you really do think about all of these things, on your own terms.

I’ll be watching Matt Ross’s career with interest, this being just his second full-length feature, which he has also written. Not many directors succeed in creating such a genuinely balanced piece of thought-provoking cinema.

It’s hard to find screenings for, but I’d suggest it’s worth the time to track down – and certainly one to grab off Amazon or iTunes as soon as it appears.