Linguist Dan Everett is again stirring controversy for his work on the language of the Pirahã people in northwest Brazil.

Everett first met the tribe as a Christian missionary. In 2005, he published a paper outlining his claims about the Pirahã language and followed up in 2008 with a book about his experiences.

With a new book, Language: The Cultural Tool, out this month and a documentary, The Grammar of Happiness, on the way, Everett is facing criticism that he is exploiting indigenous people for his own gain. Other linguists also say his work on the Pirahã language and culture can't be verified.

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How Do You Say ‘Disagreement’ in Piraha? (The New York Times 3/22)