Mark Zuckerberg said he expects advancements in the technology to take a decade before it will be ready to tackle hate speech.

It will be five to 10 years before artificial intelligence can reliably identify online hate speech and distinguish it from legitimate political debate, Facebook CEO Mark Zuckerberg testified before the U.S. Senate today.

Facebook has tested AI for detecting hate speech but found it error-prone, Zuckerberg said. AI used for this purpose needs to make nuanced judgments and be able to understand multiple languages, he said.

“Determining if something is hate speech is very linguistically nuanced,” he said, according to various transcripts of his testimony. “You have to understand what’s a slur and whether something is hateful.”

Facebook employs more than 20,000 people in security and content review, he said, and when a user flags something as offensive, these staffers examine it and take it down if it violates the site’s policies. “Some problems lend themselves more easily to AI solutions than others,” he said, and hate speech is one of the difficult ones.

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