As past statements of Imam Feisal Abdul Rauf continue to surface, many Americans have concluded that the would-be builder of a mosque at Ground Zero is lying when he calls himself a “moderate” representative of his faith. The more disturbing possibility, however, is that he’s telling the truth — that Rauf is indeed the voice of mainstream Islam.

One indication is the resounding silence from the rest of the Islamic community. If that community were truly moderate — as we in the West understand the term — one might expect it to distance itself from a man who blames the U.S. for the 9/11 attacks, says we have more innocent blood on our hands than al-Qaeda, and refuses to disown the genocidal agenda of Hamas.

A few brave Muslim individuals have indeed come out against the mosque, but they are exceptions. Where are the large numbers of Muslims who find Rauf’s statements offensive? Where are their organizations and institutions? Why aren’t they weighing in to repudiate Rauf and his apparent aims?

It’s a common problem. Each time some new offense is perpetrated in the name of Islam — whether it’s the latest suicide bombing in a public square or a woman’s being beaten and mutilated by her own family — it is mostly Western leaders and the press who voice their disapproval. The more one looks for the larger Muslim community to denounce the violence, the more “moderate Islam” seems to vanish like a mirage in the desert.

Why this is so — what happened to moderate Islam and what sort of hope we may have for it in the future — is the subject of Robert Reilly’s brilliant and groundbreaking new book, The Closing of the Muslim Mind. Reilly is a veteran of the Reagan White House, director of the Voice of America under George W. Bush, a board member of the Middle East Media Research Institute, and a frequent contributor to numerous national publications. He has made a deep dive into Muslim thought and history to discover the sources of the present Islamic condition.

The result is anything but dry. Closing is a page-turner that reads almost like an intellectual detective novel. It is among those few brave books on Islam — others would include Samuel Huntington’s Clash of Civilizations and Andrew McCarthy’s recent The Grand Jihad — that should be read by anyone who wants to understand one of the most fundamental causes of conflict in the 21st century.

Reilly does in fact locate the elusive moderate Islam — back in the 8th and 9th centuries, when the rationalist Mu’tazilites dominated Islamic thought under Caliph al-Ma’mun. The period is often referred to as the “golden age of Islam,” when that civilization produced some of its highest achievements in philosophy and science. It didn’t last. In 849, the second year of the reign of Caliph Ja’afar al-Mutawakkil, the Mu’tazilites were overthrown. Holding Mu’tazilite beliefs became a crime punishable by death, and the decidedly anti-rationalist Ash’arites soon came to dominate the faith, as they would continue to do, in one form or another, through the modern era.

What makes Closing so compelling is Reilly’s ability to tie seemingly arcane questions of Islamic theology to many of the characteristics of Islamic civilization that we in the West find so hard to fathom. Fundamentally, Ash’arism was a rejection of “natural law” and reason in favor of an all-powerful God of pure will and power. The idea of an ordered universe that behaves according to certain ordained laws — whether moral or physical — would have been understood by the Mu’tazilites. For the Ash’arites, this was blasphemy, an outrage against God’s omnipotence.

In the language of philosophy, this way of looking at the world is known, somewhat confusingly, as “voluntarism.” To quote Reilly, it “holds that God is the primary cause of everything and there are no secondary causes. There is no causal mediation. Therefore, what may seem to be ‘natural laws,’ such as the laws of gravity, physics, etc. are really nothing more than God’s customs or habits, which He is at complete liberty to break or change at any moment.”

While Christianity recognizes the possibility of miracles, when God intervenes to supersede natural law, in Islam every nanosecond is the functional equivalent of a miracle, the result of God’s divine act. Thus there is no law of gravity, only God’s will, determining moment by moment that the apple will fall from the tree. Neither is there any morality, no objective good and evil as we in the West would see it, only the arbitrary decrees of an all-powerful God. There is no “truth that is written in our hearts,” only the truths that are written in the Koran, which could just as well be otherwise if such were the whim of God. As Ibn Hazm pronounced in the 11th century, “He judges as He pleases, and whatever He judges is just. . . . If God the Exalted had informed us that He would punish us for the acts of others . . . all that would have been right and just.”

The problem, one might say, is obvious. In science, the repudiation of natural law meant the explicit denial of cause and effect. No wonder that the rise of the Ash’arites coincided with the decline of a once-vibrant Islamic intellectual culture after the 13th century. And no wonder that societies that exalt the power and arbitrary will of God to the exclusion of reason can hardly understand, let alone embrace, modern democratic institutions, which are founded, as our Declaration of Independence makes clear, in the self-evident and enduring truths of natural law.

Nor can we be surprised that such cultures endorse institutionalized domestic violence or rampant terrorism and the murder of innocents. As hard as it is for the secular Left to accept, Western culture is founded on and steeped in the Judeo-Christian assumption that our innate understanding of what is right is a direct reflection of God’s goodness and justice as reflected in His universal law, to which even He adheres. We make a mistake when we assume other cultures are necessarily speaking the same moral language.

Is there a possibility that Islam can find its way back to the root philosophies of its golden age? There are those within Islam who want to, but — like the voices raised in opposition to the mosque — they are lonely, even threatened, outposts within their faith. One thing Reilly’s account makes clear: Only when we move beyond the common platitudes of our contemporary political discussion and begin to deal with Islam as it really is — rather than the fiction that it is the equivalent of our Western culture dressed up in a burqa — will we be able to help make progress in that direction.

– Josh Gilder is one of the founding directors of the White House Writers Group.