Each new Islamic terrorist atrocity is denounced by western leaders such as our Prime Minister as a ‘twisted’ or ‘perverted’ version of Islam, the ‘Religion of Peace’. True Muslims, they emphasise, are peace-loving and tolerant. What this really amounts to is a way of saying: ‘Look how broad-minded I am! I have nothing against true Islam! Also I am learned enough in Islamic doctrine to distinguish between false and true Islam.’

Unfortunately, this is merely self-promoting codswallop. There is no ‘true’ version of Islam, and there is no false version. Or rather, there is no way of judging which is true and which is false.

It is a safe bet that many of those who deplore what they claim is a departure from Islam have only a vague idea of what Islam is and what the Islamic texts teach. The ‘true’ version as evoked here means simply ‘The one I find it most agreeable or reassuring to claim is definitive,’ or perhaps, ‘I know that Christianity extols peace. Therefore all other religions must do likewise’. Or: ‘If I say terrorism and beheading are not attributes of true Islam, I may persuade the terrorists and head-choppers to become more peaceful.’

There is no religious equivalent to the High Court of Australia or the US Supreme Court, whose judgements are taken as final, at least until they are superseded, to say what is true and what is not.

If a ‘true’ version of Islam exists anywhere it might be expected to be in Saudi Arabia, its birthplace. In 2002, 15 school-girls were burnt to death there when their school caught fire and religious police pushed them back into the flames as they weren’t properly dressed. True Islam?

The Pope is held by Catholics to be infallible on certain doctrinal and historical matters, but only by Catholics, and in fact Papal infallibility is a lesser claim than some think – it means only that the Pope’s decision is final, just as, in politics and law, the minutes of a cabinet meeting or a court of appeal are taken as final, regardless of what was actually said, because this is the only way to get business done and avoid endless quarreling.

There are a number of frequently bitterly-fighting Islamic sects, as there are a number of Christian sects, and even of Jewish sects. If you are a member of one of these, you will think it is the true faith. Every sect thinks it is true. Catholics think theirs is the true faith and Protestants are in error, and Protestants think the converse. But there is no overarching earthly power to judge which is true.

When the Muslim armies attacked Constantinople, the Christian West refused to send aid to their Orthodox brethren because of a disagreement over whether Christ was co-eternal with God the Father. Which was the true faith, and who is to say? Further, the Christian Orthodox Eastern Empire had already been pillaged and greatly weakened by the Western Christian crusaders.

It is possible to claim Nazism is a twisted version of Wagner and Nietzsche, and Marxism a twisted version of Judeo-Christianity, but a Nazi or a Marxist would not agree. Historian Manning Clark constantly likened Lenin, the interpreter and developer of Marx, to Christ, Lenin’s millionfold murders notwithstanding.

S. Lewis made an effort, consulting both Protestant and Catholic theologians, to strip Christianity of sectarian differences and reduce it to its essentials in the book Mere Christianity. But what ‘mere Christianity’ is, like what ‘true Islam’ is, remains subjective.

Could there be a ‘mere Islam’ from which the true shape of the religion might be discerned? Well, it might be said that there is, in the Koran, and it is easily referred to. But the Koran is not consistent, with the later, blood-thirsty passages extolling war, conquest and the subjugation of women being generally held to supersede the earlier ones extolling tolerance and peace. While the self-sealing nature of the Islamic writings made radical reform impossible, it did not make differences of interpretation impossible.

If the Prime Minister and others turn to the great universities of the Muslim world, which might be thought to be the guardians of any ‘true’ doctrine, they will frequently find a reversion to the covering of women (as was not the case a few years ago), teachings that Jews are descended from pigs and monkeys and the promotion of jihad. One can, however, discern the general shape of a religion by a kind of gestalt process of observing it in history. Thus, with virtually no exceptions, Islam has, from its earliest days, been spread by war and conquest. The peaceful and mystical sects of Islam have existed behind the blood-soaked frontiers in territories the warriors have pacified. The non-Muslim part of the world is known as the ‘house of war’. Forcible conversion at sword-point has been unknown, with only the rarest exceptions, in Christianity, at least for the last thousand years, but is general and taken for granted in Islam. Today practically every Muslim-majority district in Europe, particularly in France, has become a no-go area for other religions and even for the civil authorities. Jews are fleeing from France and other European countries with large Muslim populations..

When, in Australia, the visit of Ayaan Hirsi Ali had to be cancelled, following threats that 5,000 Muslims would turn out for implicitly violent demonstrations against her, were all the 5,000 followers of a ‘twisted’ form of the religion? Are the thousands following Isis or Boko Haram? Says who?

The impossibility of settling upon a definition of ‘true’ Christianity and ‘true’ Islam does not alter the fact that Presbyterians, Catholics, Anglicans and Methodists do not as a rule fly airliners into buildings. The activity of Christian medical missions in Africa today is not generally accompanied by demands for conversion, although conversion is held to be desirable. Thus, with exceptions, ambiguities and nuances, the general shape of these religions, both in history and in the world today, can be made out pretty clearly. Their processes are sometimes subtle: Christianity, for example, did not, in the scriptures, specifically condemn what we see as the obvious evils of slavery and torture, but its expressed values – by the commandment ‘love one another’ – gradually made slavery and torture unthinkable in Christian civilisation.

The Jewish conception of slavery was more in the nature of entering into a bond to pay off a debt than it was life-long chattel slavery. Islam, however, actively condoned the enslavement of captives through the ages. Christianity also made war a matter of reluctance rather than enthusiasm, a regrettable necessity rather than a duty. Next time someone says jihadists do not represent the true faith, just ask them to define the true faith or its keepers.