By winning territory and diminishing the size of areas ruled by non-Muslims, jihad accomplishes two goals: it manifests Islam’s claim to replace other faiths, and it brings about the benefit of a just world order. In the words of Majid Khadduri of Johns Hopkins University, writing in 1955 (before political correctness conquered the universities), jihad is “an instrument for both the universalization of [Islamic] religion and the establishment of an imperial world state.”

As for the conditions under which jihad might be undertaken—when, by whom, against whom, with what sort of declaration of war, ending how, with what division of spoils, and so on—these are matters that religious scholars worked out in excruciating detail over the centuries. But about the basic meaning of jihad—warfare against unbelievers to extend Muslim domains—there was perfect consensus. For example, the most important collection of hadith (reports about the sayings and actions of Muhammad), called Sahih al-Bukhari, contains 199 references to jihad, and every one of them refers to it in the sense of armed warfare against non-Muslims. To quote the 1885 Dictionary of Islam, jihad is “an incumbent religious duty, established in the Qur’an and in the traditions [hadith] as a divine institution, and enjoined especially for the purpose of advancing Islam and of repelling evil from Muslims.”

JIHAD WAS no abstract obligation through the centuries, but a key aspect of Muslim life. According to one calculation, Muhammad himself engaged in 78 battles, of which just one (the Battle of the Ditch) was defensive. Within a century after the prophet’s death in 632, Muslim armies had reached as far as India in the east and Spain in the west. Though such a dramatic single expansion was never again to be repeated, important victories in subsequent centuries included the seventeen Indian campaigns of Mahmud of Ghazna (r. 998-1030), the battle of Manzikert opening Anatolia (1071), the conquest of Constantinople (1453), and the triumphs of Uthman dan Fodio in West Africa (1804-17). In brief, jihad was part of the warp and woof not only of premodern Muslim doctrine but of premodern Muslim life.

That said, jihad also had two variant meanings over the ages, one of them more radical than the standard meaning and one quite pacific. The first, mainly associated with the thinker Ibn Taymiya (1268-1328), holds that born Muslims who fail to live up to the requirements of their faith are themselves to be considered unbelievers, and so legitimate targets of jihad. This tended to come in handy when (as was often the case) one Muslim ruler made war against another; only by portraying the enemy as not properly Muslim could the war be dignified as a jihad.

The second variant, usually associated with Sufis, or Muslim mystics, was the doctrine customarily translated as “greater jihad” but perhaps more usefully termed “higher jihad.” This Sufi variant invokes allegorical modes of interpretation to turn jihad’s literal meaning of armed conflict upside-down, calling instead for a withdrawal from the world to struggle against one’s baser instincts in pursuit of numinous awareness and spiritual depth. But as Rudolph Peters notes in his authoritative Jihad in Classical and Modern Islam (1995), this interpretation was “hardly touched upon” in premodern legal writings on jihad.

IN THE vast majority of premodern cases, then, jihad signified one thing only: armed action versus non-Muslims. In modern times, things have of course become somewhat more complicated, as Islam has undergone contradictory changes resulting from its contact with Western influences. Muslims having to cope with the West have tended to adopt one of three broad approaches: Islamist, reformist, or secularist. For the purposes of this discussion, we may put aside the secularists (such as Kemal Atatürk), for they reject jihad in its entirety, and instead focus on the Islamists and reformists. Both have fastened on the variant meanings of jihad to develop their own interpretations.

Islamists, besides adhering to the primary conception of jihad as armed warfare against infidels, have also adopted as their own Ibn Taymiya’s call to target impious Muslims. This approach acquired increased salience through the 20th century as Islamist thinkers like Hasan al-Banna (1906-49), Sayyid Qutb (1906-66), Abu al-A‘la Mawdudi (1903-79), and Ayatollah Ruhollah Khomeini (1903-89) promoted jihad against putatively Muslim rulers who failed to live up to or apply the laws of Islam. The revolutionaries who overthrew the shah of Iran in 1979 and the assassins who gunned down President Anwar Sadat of Egypt two years later overtly held to this doctrine. So does Osama bin Laden.

Reformists, by contrast, reinterpret Islam to make it compatible with Western ways. It is they—principally through the writings of Sir Sayyid Ahmad Khan, a 19th-century reformist leader in India—who have worked to transform the idea of jihad into a purely defensive undertaking compatible with the premises of international law. This approach, characterized in 1965 by the definitive Encyclopedia of Islam as “wholly apologetic,” owes far more to Western than to Islamic thinking. In our own day, it has devolved further into what Martin Kramer has dubbed “a kind of Oriental Quakerism,” and it, together with a revival of the Sufi notion of “greater jihad,” is what has emboldened some to deny that jihad has any martial component whatsoever, instead redefining the idea into a purely spiritual or social activity.

For most Muslims in the world today, these moves away from the old sense of jihad are rather remote. They neither see their own rulers as targets deserving of jihad nor are they ready to become Quakers. Instead, the classic notion of jihad continues to resonate with vast numbers of them, as Alfred Morabia, a foremost French scholar of the topic, noted in 1993:

"Offensive, bellicose jihad, the one codified by the specialists and theologians, has not ceased to awaken an echo in the Muslim consciousness, both individual and collective. . . . To be sure, contemporary apologists present a picture of this religious obligation that conforms well to the contemporary norms of human rights, . . . but the people are not convinced by this. . . . The overwhelming majority of Muslims remain under the spiritual sway of a law . . . whose key requirement is the demand, not to speak of the hope, to make the Word of God triumph everywhere in the world."

In brief, jihad in the raw remains a powerful force in the Muslim world, and this goes far to explain the immense appeal of a figure like Osama bin Laden in the immediate aftermath of September 11, 2001.