Before beginning this section I think it would be helpful to define a few words.
First, "orthodoxy" and "heresy." Both words carry connotations of praise or blame that I'd like to avoid, if possible. The point I'd like to stress here is that neither means anything if asserted without reference to a specific religious group. To take a simple example, to say that "God has an only-begotten son" is orthodoxy in Christianity and heresy in Judaism or Islam. In other words, to assert that something is orthodox or heretical only makes sense by saying that it is so in relation to some particular set of doctrines.
By the same token, though the terms "corruption" and "reform," in the context of religion, both refer to a change, the one refers a blameworthy change with respect to orthodoxy, one which distorts and denies orthodoxy, and the other refers to a salutary change with respect to orthodoxy, which restores orthodoxy and corrects heresy. Whether the "new thing" restores or obscures orthodoxy depends, naturally, on what one thinks orthodoxy is in the first place.
So what exactly is Islam? It is obviously a "World Religion," quite a major religion with something over a billion adherents at last count. Like the other two dominant Western world religions, Judaism and Christianity, it has an ascertainable set of dogmas (one God, creator, transcendent, as proclaimed by a final prophet, Muhammad), a set of holy writings (most importantly, the Qur'an), and a distinctive law, ethics, style of worship and organization. Like most major religions it has some major divisions (the Sunni/Shi'ite split) and innumerable smaller ones, most within and among the "big two."
But to simply list the distinctive characteristics of Islam can obscure what I think is most germane to the inquiry here, how its adherents should be viewed as Western and Islamic civilizations come to intermingle.
My central point is that, from the point of view of Christianity, Islam is best understood as a heresy, and that, from the point of view of Islam, both Christianity and Judaism are best understood as corrupt forms of an Islam that has existed since the time of the biblical Patriarchs, restored and reformed by Muhammad.
This relationship is sometimes papered over with the innocuous and accurate-as-far-as-it-goes description of Judaism, Christianity and Islam as the "Abrahamic religions." All do indeed look back to the figure of Abraham as an exemplary figure; but they also all three look back to Noah, and the antediluvian patriarchs, and Adam. So in a sense to suggest that Abraham is a uniquely uniting figure can be misleading. More accurate is to see how Moses is the determinate figure of Judaism (revered by Christians and Muslims), Jesus is the determinate figure of Christianity (revered by Muslims), and Mohammed the determinate figure for Islam.
So though they are far from constituting a single religion, they do constitute three singularly similar religions, with Islam closer, religiously, to Judaism than Christianity, just as the careers of Moses and Muhammad, as political leaders and lawgivers, are more similar to each other than to the career of Jesus.
Christianity is arguably distinctive in having a soteriology that presumes the existence of a divine law that has itself become a hinderance to the reconciliation of God and man. To put it another way, in Judaism and Islam the tension beween law and grace are less central than in Christianity, where the redemptive death of the Son has a unique role. But Judaism, even before the advent of Christianity, gave rise to the prophetic movement, as a critique of the law and the cult that is the object of so much of the law, and after the destruction of the second temple a long and complex series of legal and theological developments continued to give rise to a way of life rooted in the law, but by no means merely "legalistic." Similarly, in Islam, the law there newly proclaimed, not radically different in its ethical standards from Jewish law, is subject to a God who is repeatedly "the compassionate, the merciful," and whose severe judgments on lawbreakers do not preclude God's continuing willingness to forgive. As in Judaism the formal priority of the divine law is mitigated by a long and subtle history of legal, theological and philosophical development. There is also the express appeal to the heart in movements such as Sufism, an appeal whose point is not an opposition to the law, but, in a figure such as al-Ghazali, having a "completing" effect on one already a formidable shaper of law and philosophy.
Despite popular claims, I don't see great discrepancies between Islam's ethics and those of Judaism and Christianity. There are differences, of course. Islam allows limited polygamy, for instance, but the practice is hardly widespread, and certainly less common than the "serial polygamy" of marriage and divorce and re-marriage so common in contemporary Christianity. Some see in the Qur'an a violent attitude to non-Muslims, and I am familiar with the passages that give rise to those concerns. But I also can't help but note that there are similar passages in the Hebrew and Christian scriptures that with similar justification have grounded polemics contending that Judaism and Christianity are inherently violent and intolerant. But in practice, so far as I can tell, ordinary Muslims try to be honest, generous, hard-working and forgiving, pretty much as ordinary Jews and Christians do.
The conclusion of this is that the religion of Islam is sufficiently similar enough to the religions of Judaism and Christianity that I do not see that there is any religious impediment to Jews, Christians and Muslims living together in peace as citizens of religion-neutral republics. Those differences that are undoubtedly there need not necessarily lead to attempts to dominate. Of course religious differences will give rise to political differences, but the resolution of those differences by means of representative government with fundamental rights of speech, press, assembly and religion protected, means that those differences need not undermine the common polity.
But, one might respond, Islam is more than a religion. It is also a polity, a culture, a civilization, and that fact arguably creates problems above and beyond those posed simply by the religion. It is to that contention I hope to turn in the next installment of this series.