Late in 1545, a general council of the Western Church was convened by Pope Paul III in the Tyrolean city of Trent. The ambition of the various bishops and theologians in attendance was to affirm Catholic doctrine in the face of the Protestant Reformation. Accordingly, when the council issued its first significant decree on 8 April 1546, it was targeted very precisely at what the delegates saw as most noxious about Luther and his followers. Whereas Protestants, following Luther’s lead, aspired to strip away the cladding of tradition and learn the will of God from scripture alone, the Council of Trent condemned this ambition as a pernicious heresy. Divine revelation, it declared firmly, was not confined to the Bible. Tradition, too, “preserved in the Catholic Church by a continuous succession”, expressed the essence of Christ’s teachings. To doubt this was no longer to rank as Christian.

It is in a kindred spirit that Mehdi Hasan, in his article in last week’s issue of the New Statesman, would deny the title of Islamic to Islamic State, also known as Isis. That Isis militants, in justifying their actions, can quote the Quran, or the example or sayings of the Prophet Muhammad, does not necessarily make them orthodox Muslims. Islam, like Christianity, is more than the sum of its scriptures. Over the course of its near 1,500 years of existence, an immense corpus of commentary and interpretation has accrued. “. . . the religion’s teachings in every age are determined by scholarly consensus on the meaning of the complex scriptural texts.” So declares Timothy Winter, the director of the Cambridge Muslim College, as quoted by Hasan. It is an assertion that would not have looked out of place in the decrees of the Council of Trent.

The problem faced by the orthodox religious authorities in the Muslim world, however, is very similar to that which confronted the Catholic Church in the 16th century: escaped genies are tricky things to get back into bottles. The same impulse that prompted Luther to affirm the primacy of scripture over Catholic doctrine has also long been at work in Islam. As far back as the 13th century, a scholar based in Damascus by the name of Ibn Taymiyya proposed that the surest way to know God’s purpose was to study the practices of the first three generations of Muslims: the “forebears”, or “Salafs”. Reports of what Muhammad and his earliest followers had done, so he argued, should always trump subsequent tradition. Like Luther, Ibn Taymiyya was condemned as a heretic; but he also, again like Luther, blazed a momentous trail.

Salafism today is probably the fastest-growing Islamic movement in the world. The interpretation that Isis applies to Muslim scripture may be exceptional for its savagery – but not for its literalism. Islamic State, in its conceit that it has trampled down the weeds and briars of tradition and penetrated to the truth of God’s dictates, is recognisably Salafist. When Islamic State fighters smash the statues of pagan gods, they are following the example of the Prophet; when they proclaim themselves the shock troops of a would-be global empire, they are following the example of the warriors of the original caliphate; when they execute enemy combatants, and impose discriminatory taxes on Christians, and take the women of defeated opponents as slaves, they are doing nothing that the first Muslims did not glory in.

Such behaviour is certainly not synonymous with Islam; but if not Islamic, then it is hard to know what else it is.

Admittedly the actions of those signed up to Islamic State are unlikely to have been inspired exclusively by religious teachings. Many of those fighting for Isis may indeed, as Hasan points out, be varnishing their taste for violence or power with a sheen of piety. But the same was true of those inspired by Luther’s teachings – not to mention the early Muslims themselves.

Back in the time of the Salafs, avarice and religiosity frequently coincided. When a slave revolt erupted in Syria and Iraq less than 50 years after the death of Muhammad, the Arab conquerors were outraged. “These slaves are our booty,” one of them exclaimed. “They were granted us by God!”

Jihadis in Raqqa have tweeted in similar tones about uppity Yazidi slaves. To imagine that religious motivation can somehow be isolated from the complex swirl of ambitions, fears and desires that constitute human nature is to fall for an illusion: that religions, contingent as they are, and as subject to evolution as any other manifestation of culture, exist platonically as abstract ideals.

The truth is that in Islam today, as in Christianity during the Reformation, the spectrum of those who practise the faith is widening to convulsive effect. Hasan’s dismissal of two Isis recruits from Birmingham as “religious novices” echoes the horror of Catholic scholars such as Thomas More at the pretensions of Protestant tailors and tinkers. Just as in the early 16th century the printing press and the efforts of translators such as Luther and Tyndale served to democratise knowledge of the Bible, so in the 21st century has the ready availability on the internet of the Quran and the hadiths in the vernacular enabled rappers, security guards and schoolgirls all to bandy scripture. To complain that quranic verses which mandate crucifixion or beheading are being cited without reference to the traditions of Islamic jurisprudence is to miss the point. It is precisely because Isis militants imagine themselves the equivalent of Muhammad’s companions, blessed with an unadorned understanding of God’s commands, that they feel qualified to establish a caliphate.

“My people,” so Muhammad is once said to have warned, “are destined to split into 73 factions – all of which, except one, will end up in hell.” Who, then, Muslims have often wondered, will gain paradise? Isis, like so many of the various other sects that have emerged in the course of Islamic history, appears confident of the answer.

It is not merely coincidence that IS currently boasts a caliph, imposes quranically mandated taxes, topples idols, chops the hands off thieves, stones adulterers, exec­utes homosexuals and carries a flag that bears the Muslim declaration of faith. If Islamic State is indeed to be categorised as a phenomenon distinct from Islam, it urgently needs a manifest and impermeable firewall raised between them. At the moment, though, I fail to see it.

Tom Holland is a historian and the author of “In the Shadow of the Sword” (Abacus). This is a response to Mehdi Hasan’s NS essay “How Islamic is Islamic State?”