There may be no more globally divisive question over the past few years than whether the Islamic State is representative of the world's global Muslim population. Speaking in Rome on Tuesday, U.S. Secretary of State John F. Kerry waded into this controversial debate yet again – and took a remarkably strong position for a Western leader.

“Daesh is in fact nothing more than a mixture of killers, of kidnappers, of criminals, of thugs, of adventurers, of smugglers and thieves,” Kerry said. “And they are also above all apostates, people who have hijacked a great religion and lie about its real meaning and lie about its purpose and deceive people in order to fight for their purposes.”

The use of the word "apostates" – a term to describe someone who renounces or abandons their religion – has raised eyebrows among observers. The description has been commonly used by extremist groups: The Islamic State has justified its attacks on Muslims with rhetoric that suggests these Muslims were apostates, which it views as a crime punishable by death.

On Twitter, Nasser Weddady, a popular online activist who grew up in Syria, mocked Kerry for his comment. Wedaddy and others also jokingly suggested that Kerry was a "takfiri," a word used to describe a Sunni Muslim who accuses others of apostasy.

This appears to be at least the second time Kerry has publicly used the word to describe the Islamic State. While talking about the group at a conference in Washington in December, Kerry described the group as a "a mixture of killers and kidnappers, smugglers, thieves, and apostates who have hijacked a religion and combined a medieval thinking with modern weapons to wage an especially savage brand of war.”

Back then, Shadi Hamid, a senior fellow at the Brookings Institution and expert in Islamist movements, explained why he felt Kerry's use of the word was problematic.

Few would argue with Kerry's intentions here. He clearly seems to be attempting to distance the Islamic State from mainstream Muslims, a reasonable and perhaps even honorable reaction to the more inflammatory comments by some of his peers.

In fact, the use of the term apostate is just Kerry's latest bid to create that rhetorical distance. The secretary of state has been a prominent Western user of the word Daesh, an Arabic acronym widely used to refer to the Islamic State in the Middle East. Supporters of the use of that word say it creates a clearer boundary between the "Islamic State" and the broader Islamic community. (Another factor in its use may be reports that the Islamic State itself hates the word due to its similarity to another Arabic word meaning to trample or crush.)

Kerry isn't the only Western leader attempting this line of attack: Obama has openly said that the Islamic State is "not Islamic," while British Prime Minister David Cameron has voiced his support for the viral "You ain't no Muslim, bruv" catchphrase. The theological line of thinking from non-Muslims seems to leave a bad taste in some mouths, however. Hamid and his Brookings colleague Will McCants have written that there's "something odd about an American president or Secretary of State opining on what is and isn’t legitimately Islamic."

Some world leaders seem to concur: In a recent interview with my colleague Ishaan Tharoor, Australian Prime Minister Malcolm Turnbull suggested that no one would take his views on Islamic theology ("assuming I had any") very seriously as he was the leader of a "Western secular nation."

It's unclear why Kerry has felt the need to ratchet up his rhetoric recently. It's not like the world is wanting for examples of Muslim leaders and figures condemning the Islamic State as un-Islamic – it's been a recurring and widespread criticism of the group for years now. However, important religious bodies such as the al-Azhar Mosque in Cairo have stopped short of labeling the group apostates – perhaps aware of the weight the word carries. Presumably, the secretary of state doesn't actually think apostasy is a crime, which makes the choice of words even more confusing.

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