Did French philosopher Voltaire say, "To learn who rules over you, simply find out who you are not allowed to criticize"? No, that's not true: Two academic authorities on Voltaire told Lead Stories the words were not those of the French writer and philosopher. Meanwhile, a white nationalist has declared he created the phrase in 1993.
The claim reappeared in a Facebook post (archived here) where it was posted on August 3, 2021. The post read:
To learn who rules over you, simply find out who you are not allowed to criticize. Voltaire
This is what the post looked like on Facebook at the time of writing:
(Source: Facebook screenshot taken on Tue Aug 10 14:19:31 2021 UTC)
Kevin Strom, described by the Southern Poverty Law Center in its extremist files as "arguably the only true intellectual remaining in the American neo-Nazi movement," laid claim to the phrase in an article he published in 2017. Strom said in the article, which was titled "Voltaire Didn't Say It," he created the phrase and first used it in a 1993 broadcast.
"Whoever hijacked my quote and put it over Voltaire's signature liked what I was saying," Strom wrote in the 2017 article. "But he didn't dare attribute it correctly. He didn't dare make his point with a quote from a known 'racist' or 'anti-Semite,' no matter how good the quote was."
Two experts on Voltaire's works agreed that the phrase did not originate with Voltaire, and they confirmed that Strom was the apparent source.
Paul Gibbard, a senior lecturer at the University of Western Australia and an expert on Voltaire responded to an inquiry from Lead Stories with this response on August 9, 2021:
This phrase is not actually by Voltaire, although it has often been attributed to him.
The origins of the phrase are discussed in this article in the Guardian from 2015, in which the journalist Elle Hunt explains that it may have first been used by someone named Kevin Strom, who is said to be a neo-Nazi.
The phrase is also discussed in Nicholas Cronk's book 'Voltaire: A Very Short Introduction' (Oxford, 2017), p. 122, who says the phrase was first used by Strom in 1993.
Matching Gibbard's findings, Thomas Kaiser, a French history professor at the University of Maryland College Park, told Lead Stories on August 10, 2021:
I have looked into the question of whether Voltaire ever said/wrote "To learn who rules over you, simply find out who you are not allowed to criticize." The answer is almost certainly not. Here are my reasons:
1) Many attribution of quotations to Voltaire (and other famous witty individuals like Churchill) turn out to be false and were originally invented simply to lend greater authority to them.
2) Reputable scholars and scholarly organizations like the Voltaire Foundation have denied the attribution. To the best of my knowledge, no one has located the source of the quotation in any of Voltaire's works.
3) The quotation either originated with or was propagated by an anti-Semitic Holocaust denier named Kevin Strom, who was protesting the alleged suppression of his, in fact, baseless claims. Interestingly, Strom denied that the quotation came from Voltaire so that he could claim credit for it himself. Here is the website in which he did so.
In sum, no one has proved the attribution as far as I know, and the overwhelming consensus is that Volatire never made this statement.