Manohla Dargis, New York Times, sets up the plot:

For years, [Ben] and his ailing dream of a wife, Leslie (Trin Miller), have been living with their six kids…on a compound where they have thrived beautifully without electricity, a sewer line or trend alerts about the Kardashians. By day, Ben teaches and trains the children, racing them through the woods like Olympians or Special Forces soldiers. At night, the family plays music together and reads by firelight — leafing through books one page at a time — before bedding down in the communal tepee…

Ben and Leslie have opted to live in seclusion as a matter of principle, having embraced protest as an ideal. At its loftiest, their profound seclusion suggests that they’re spiritual and philosophical heirs to an isolationist like Henry Thoreau; at worst, it suggests fanaticism, cultishness, selfishness…

Instead of holidays like Christmas, the Cash family celebrates Noam Chomsky Day. By way of introducing the noted social philosopher here, one sampling I found of Chomsky is quite relevant to today’s political theater: “The more you can increase fear of drugs, crime, welfare mothers, immigrants and aliens, the more you control all of the people.”

A quote that becomes germane to Captain Fantastic and is voiced by a well-learned Cash child: “If you assume that there is no hope, you guarantee that there will be no hope. If you assume that there is an instinct for freedom, that there are opportunities to change things, then there is a possibility that you can contribute to making a better world.”

David Edelstein, Vulture: “You could actually think of the movie as Noam Chomsky’s Little Miss Sunshine.”

Let me explain further…

A major turning point early on involves a crisis regarding Leslie’s mental health. We learn she’s been away for months in order to get help for her bipolar disorder—but soon enough we also find out she’s killed herself. Not fans of Ben’s influence on their daughter, her parents (Frank Langella and Ann Dowd) bar him from the funeral, which becomes yet another thing to protest.

Justin Chang, Los Angeles Times: “...(T)he Cashes decide to steer their bus toward the big city, crash Mom’s church funeral and honor her wish to be cremated in a Buddhist ceremony.”

A brief summary of what ensues (Alonso Duralde, The Wrap): “Just when you think the film is smugly poising Ben’s rebel-outsider mentality against the close-mindedness of his late wife’s parents, ‘Captain Fantastic’ steps up and acknowledges that some of Ben’s parenting techniques might actually be endangering his own children, and it makes the case that home-schooling and living off the land can be great and valuable, but socialization skills can come in handy as well.”

Watch the trailer for Captain Fantastic below: