“Captain Fantastic” is an inexplicably-titled film that doesn’t have to do with a captain of any sort nor anything particularly fantastic.

If the film was inspired by “O Captain! My Captain!,” Walt Whitman’s poem about the assassination of President Abraham Lincoln, it’s not apparent.

Nor is it evident that the film was inspired by the 1975 Elton John album, “Captain Fantastic and the Brown Dirt Cowboy,” and the title song’s semi-gibberish lyrics by Bernie Taupin.

In “Captain Fantastic,” Ben (Viggo Mortensen) and his wife are raising six children in the Pacific Northwest forest.

The mother takes ill and Ben is forced to choose between his hippie survivalist wilderness lifestyle, the tug of the in-laws (Steve Zahn and Kathryn Hahn as the parents), the demands of a wealthy grandfather (Frank Langella) and the growing independence of two of the sons who question and resent the parents’ back-to-nature lifestyle choice.

Because the screen time is divided among the six child characters and Ben mostly appears opposite them, the screenplay lacks sufficient character development. The philosophy of Noam Chomsky and other left-wing political viewpoints are recited dutifully by Ben and his children. It’s TV’s “Family Ties” (1982–1989) meets “Swiss Family Robinson” (1960) somewhere north of Seattle.

Writer-director Matt Ross (writer-director, “28 Hotel Rooms,” 2012) tells the story realistically, almost documentary film style. The cabin, tee-pee and tree house in the woods are believably depicted. The green-painted former metro bus that Ben drives with the children inside is a throw-back to the late 1960s and early 1970s ethos of dropping out of society, including the Yippie tenet of liberating merchandise, i.e., stealing.

The screenplay effectively contrasts the so-called straight life with that of living off the grid. The wisdom of such a choice in terms of raising children is brought into question.

The children undergo “training,” as the father calls it, in martial arts, among other boot camp activities; sing and play music together; learn how to hunt for food; can recite the United States Constitution Bill of Rights, have a reading list that includes Fyodor Dostoyevsky’s 1880 novel, “The Brothers Karamazov,” and other literature classics, but are ill-equipped to handle the real world. “Unless it comes out of a book, I don’t know anything,” complains one son.

Mortensen presents an unrelenting intensity as the father convinced of his own moral superiority. His scenes with the always excellent Langella are among the film’s best. As Bo, one of the sons, George MacKay has some strong scenes, as does Nicholas Hamilton as Rellian, the younger son. Samantha Isler, Annalise Basso, Shree Crooks and Charlie Shotwell play the other children.

“Captain Fantastic” is a difficult film to watch. Many of the scenes are intentionally uncomfortable. There’s a tension between the father and children that borders on child abuse. It’s one of those films that will elicit debate and discussion long after it’s over.

“Captain Fantastic,”MPAA rated R (Restricted. Children Under 17 Require Accompanying Parent or Adult Guardian) for language and brief graphic nudity; Genre: Comedy, Drama, Romance: Run time: 1 hr., 58 min.; Distributed by Bleecker Street Media.

Credit Readers Anonymous:“Captain Fantastic,” filmed on location in Washington and New Mexico, includes an acoustic version of the Guns and Roses’ song, “Sweet Child of Mine.”

Box Office,Aug. 17: “Suicide Squad” stayed at the top, No. 1 three weeks in a row with $20.7 million, $262.2 million, three weeks; with “Sausage Party” again at No. 2, $15.3 million, $65.3 million, two weeks, keeping “War Dogs” opening at No. 3, with $14.3 million; “Kubo and the Two Strings” opening at No. 4, with $12.6 million, and “Ben-Hur” at No. 5 with $11.4 million (another summer big-budget blockbuster that went bust):

6. ”Pete’s Dragon,” $11.3 million, $42.8 million, two weeks; 7. “Bad Moms,” $8.1 million, $85.8 million, four weeks; 8. “Jason Bourne,” $7.9 million, $140.8 million, four weeks; 9. “The Secret Life of Pets,” $5.8 million, $346.7 million, seven weeks; 10. “Florence Foster Jenkins,” $4.3 million, $14.4 million, two weeks.

Unreel,Aug. 26:

“Mechanic: Resurrection,”R: Dennis Gansel directs Jason Statham, Jessica Alba, Tommy Lee Jones and Michelle Yeoh in the action film as Arthur Bishop returns to try to clean up his past.

“Hands of Stone,”R: Jonathan Jakubowicz directs Robert De Niro, Ana de Armas, Ellen Barkin and John Turturro in the biography drama about Roberto Duran and his trainer Ray Arcel.

“Complete Unknown,”R: Joshua Marston directs Rachel Weisz, Michael Shannon, Kathy Bates and Danny Glover in the thriller about a man, his wife and an old flame.

Two Popcorn Boxes out of Five Popcorn Boxes