Former US Secretary of Defense Donald Rumsfeld was unfairly ridiculed for his division of knowledge into knowns and unknowns. He said that there were things that we know we know, things that we know we don't know, and things that we don't know we don't know. Convoluted language perhaps, but perfectly logical, as far as it goes. What's the matter then?

The real inadequacy of it is that it overlooks the fourth possibility: the things that we don't know we know. That is, there are things that are well known, or known to us if we make a modicum of effort, but which we deliberately overlook or turn a blind eye to: unknown knowns.

In Donald Rumsfeld's case, the unknown knowns were that Saddam Hussein had nothing to do with September 11 and that the UN weapons inspectors had searched high and low and eliminated the possibility that there were any weapons of mass destruction in Iraq. This was known, but he didn't want to know it.

The phenomenon of unknown knowns is widespread and in fact plagues the human condition. Even the existence of unknown knowns is apparently itself an unknown known. The biggest unknown knowns are in religion.

The problem is one of wilful blindness, or cognitive dissonance, to do with things that we don't want to know, because they conflict with our emotional or ideological preferences in some way. What makes it a problem is that the things we don't want to know are often highly relevant. It we took the trouble to know them, we would save a lot of time and money, and avoid a lot of needless hardship and suffering.

Mark Twain identified the phenomenon a century ago when he said "Faith is believin' what we know ain't so". That is, faith is knowing that something is not true, but believing it anyway. Faith makes the known into an unknown. Knowledge has increased enormously since Mark Twain's time. We know now that religions are contradicted, not only by each other, but by numerous facts of history, science and archaeology. Yet the knowns remain unknown.

We know, for example, that the Prophet Abraham, the legend of whom forms the basis of Judaism, Christianity and Islam, was not an historical figure, i.e. he never existed (See The Bible Unearthed, by Finkelstein et al,). The Abrahamic religions are all based on myth. One might expect that this would be a finding of some interest to those who devote their lives to belief in these religions. Yet it steadfastly remains an unknown known.

The phenomenon of propagating unknown knowns is not just one that individuals indulge in. Whole societies practise the art. With our advances in knowledge, unknown unknowns become known unknowns, and known unknowns become known knowns. Yet for whole societies, certain unknown knowns remain, and nowhere is this more so than in relation to religion. And the cost of the unknown known is higher for Islam than for any other religion.

It used to be well known that Islam was bad for modernisation, development and democracy. That is why Ataturk, the victor at Gallipoli, founded modern Turkey as a secular state. Turkey's constitution forbids the imposition of Islam. This does not prevent the government from promoting its version of Islam in schools, but it does protect Turkish society from religious strife and Islamist abuses. Despite some backsliding, Turkey is still reaping the benefits.

The United States constitution protects citizens from religious indoctrination in schools. By contrast, many Muslim countries now mandate Islam in their constitutions. Education means indoctrination. This is true of post-invasion Afghanistan and Iraq. The value of constitutional secularism was known but has become unknown. The "separation of mosque and state" is not considered. Yet this concept is not just the basis of secular democracy, but of democracy itself.

Only secularism provides a guarantee of religious freedom, which Islamic constitutions effectively forbid. Without the "freedom of thought, conscience and religion" as defined in the Universal Declaration of Human Rights, there cannot be true freedom. Yet the known has become unknown.

The Arab Spring is taking in countries that are constitutionally "Islamic states". The constitution of Egypt says "Principles of Islamic law (Sharia) are the principal source of legislation." Libya and Tunisia are following suit. Sharia law, which is the rules laid down in the Koran, cannot be overturned by an elected parliament. Thus democracy is limited and ineffective. The Arab Spring is likely to become an Islamic Winter.

Worse than that, perhaps, the whole legal system is subservient to religious leaders with the responsibility for interpreting the basic law. Koranic law can be, and is, used to justify any number of abuses, from the oppression of women, to jihad, to the killing of apostates.

Two decades ago, hijabs were rare in the Muslim world. Now they are ubiquitous. Greater prosperity, education and increased literacy have lead to more indoctrination and greater emphasis on the Koranic literalism. Exposure to slanted media intensifies belief.

Islam can only change if Muslims are able to reject the inerrancy of the Koran as Christians have generally done with the Bible. This is very hard for Muslims because the Koran demands complete acceptance, obedience and submission. If they reject any part, they can be denounced as infidels and traitors. So the knowns remain unknown due to intimidation and persecution.

The highest cost of unknown knowns relates to Islam and terrorism. Those who do not appreciate the extent to which the religious ideology of Islam is connected to insurgency and terrorism, need to know more about the Koran and Islamic history.

The Prophet Mohammed was the leader of a military insurrection. Islam was first established in the Arabian peninsular, and beyond, by means of military conquest. The Koran contains many of Mohammed's war proclamations. This is what motivates Islamic insurrections and terrorism today.

Those in doubt about this might like to consult Inspire magazine produced by Al-Qaida of the Arabian Peninsula. It is explained why, since Muslim countries have been attacked and invaded, it is the duty of all Muslims to fight the infidels. Inspiration is provided to commit the most egregious acts, all based on quotes from the Koran.

What is our counter-insurgency strategy? It has now finally been recognised that military conquest is not a sustainable counter-insurgency strategy in Iraq and Afghanistan. Building civil infrastructure is now considered a good strategy. But this is doomed to fail unless we are prepared to engage with the ideology. Failure to engage in the war of ideas is capitulation to Islam.

In the first edition of Inspire it was stated that: "Islam is not a man-made religion; it is not a religion that has been tampered with as the rabbis and priests did with the other two Abrahamic faiths." There is plenty of room for debate here. There is an opportunity to undermine the ideology of Islam based on evidence and reason. All sides would benefit from the debate.

Instead, the United States has engaged in debate with the magazine's editor in the form of a missile launched from an unmanned aircraft. Anwar al-Awlaki (a US citizen) and his colleagues were killed on September 30^th, 2011. Ex-judicial actions such as this are counter-productive. They do not provide an antidote to Islamic beliefs. They confirm them.

As societies, we cannot forever maintain the pretence that all religious beliefs are true, even when we know they are not. We need to address the issue of unknown knowns. We need to deploy reason and evidence as counter-insurgency and counter-terrorism weapons. We need to inspire a more rational world.

We know that universal ethical principles such as compassion, honesty, freedom and justice provide a basis for morality that is better than any religion. If we are honest, we will accept what reason and evidence have put beyond doubt. What is known, ought to be believed.

John L Perkins is on the Public Relations team for the Atheist Foundation of Australia and is the founding President of the Secular Party of Australia.