Even before U.S. President Barack Obama utters a word of his long-anticipated June 4 address to "the Muslim world," there is already a problem with the rhetoric. As well meaning as it sounds, the term "Muslim world" is a trap. There is no unified Muslim world. And describing it as such legitimizes the idea that it is "us vs. them" -- just the sort of divided world that al Qaeda wants to create.

To see the trouble with the term "Muslim world," one needs only to try and define it. Who is included in the Muslim world? What countries -- or individuals -- make the cut, and who defines it? Is half-Muslim Nigeria a part of the Muslim world as much as the Islamic Republic of Iran? And how do different sects in internal conflict, like the Sunni and Shia of Iraq, reconcile their placement in a single "world" to American eyes? Are extremists -- such as the Taliban or al Qaeda -- lumped together with secular Muslims?

No one questions that a religion known as Islam exists or that many Muslims believe in their global community, the ummah. As a theological reference, however, the ummah is vaguely analogous to the belief that all Christians are part of the body of Christ. It is a powerful spiritual metaphor, but not a visceral part of every believer's identity. A Muslim in Turkey, for example, might define himself as an Istanbullu first, a Turk second, and a Muslim third -- or the other way around, depending on his mood or even the time of day. (When the soccer club Galatasaray is playing, he is only a fan!) No one would claim that Guatemalans, Germans, or Guineans are the same because they are Christians, and it's equally nonsensical to lump Turks, Trinidadians, and Tunisians together simply because they also happen to be Muslim.

This term is not only an analytical error - it's also a critical public diplomacy mistake. "Muslim world" unfairly and singularly assigns adherents of Islam into a figurative ghetto. And particularly in the post-September 11, this relegation carries a real moral hazard: By lumping together extremists, secularists, and everyone in between, the term "Muslim world" legitimizes the idea that all of the group's members are locked in deadly conflict with the non-Islamic world. If this sounds dangerously close to the message through which Islamist ideologues push for jihad, it is. Extremists are the only Muslim group that strongly advocates tying all Muslims together politically, in a united global community. In their ideal world, the modern nation state would be replaced with a new caliphate under Sharia law. Every time the United States speaks to the "Muslim world," then, it inadvertently legitimizes the extremists' vision.

Thankfully, President Obama has a chance to get it right. He got off to a good start on May 4 in Ankara, where he admirably addressed the Turkish people as democrats embedded in Europe. He appealed to them as allies in the struggle against Islamist extremism while challenging them on sensitive issues, including reconciling with neighboring Armenia. At the tail end of the speech, however, he made that critical rhetorical slip: "Let me repeat: The United States is not at war with the Muslim world."

This time, as he speaks on June 4, the "Islamic world" should not make a rhetorical appearance. Instead, Obama could accentuate the rich diversity of Muslim communities around the world, referencing the Sufis of Morocco, the Shiites of Iraq, and the Sunnis of Singapore. He should recognize their accomplishments within their communities while stressing other parts of their identities, such as nationality.

As he did in Turkey, Obama should offer his broad audience a challenge. There are deep problems within Muslim communities around the world. Islamist extremists continue to push their agenda of violence and chaos. Obama should offer encouragement to the British, Egyptian, Algerian, and Iraqi Muslims (among others) who are already fighting back, taking on those extremists and reclaiming their communities. And he should recognize that the Muslim world is a figment of Osama bin Laden's imagination.