On the face of it, when professors talk of a future "clash of civilizations," two prime candidates for such conflict between cultures might be the United States and its Persian Gulf ally, Saudi Arabia.
There are great disparities, and many are obvious: America is open and democratic; its women can drive cars and hold high office. Saudi Arabia is closed and undemocratic; its women can't drive or even consider active political life.
But there are also remarkable, if rarely tallied, similarities that make their half-century strategic alliance - first in oil, lately in defense - less of a surprise.
Recognizing them is an American working in the kingdom who has spent several years here, speaks fluent Arabic, and who engages Saudis in their favorite medium: long bouts of talking. He requested anonymity due to the sensitive nature of the topic and of his work here.
"We share a similar ideological history," he says, beginning in the deliberate manner of an academic approaching a logic problem. "We both come from a tradition of intolerance and violence."
Saudi Arabia has had a "tough religious past" based on the Wahhabi sect of Islam, which imposes strict codes of behavior and dress - and a strict enforcement of Islamic law that brings a sentence of beheading for rape, murder, or drug trafficking.
"[American] religious history has also been bloody and ferocious, with people [executed] for witchcraft in New England," he says."We forget that now, but we've gone through it, and they are going through it now." The 1997 State Department human rights report on Saudi Arabia, for example, notes "freedom of religion does not exist."
"We had slavery," he adds. "They had slavery.
"We share a belief in progress, in a modern world, in divine redemption and eternal life.
"We believe we are ... kind and gentle and wonderful, and are doing someone from Mexico a favor if we let them pick our lettuce for nothing," he says. "They believe the same, and that they are helping someone if they bring them from India, Pakistan, or Sri Lanka to work and exploit them."
But the subtle differences between Americans and Saudis can be equally fundamental.
"We are always urging democracy on people, but to them we are like a teetotaler with a battleaxe," the American says. "They don't criticize their ruling family because these are the people who represent their country. They don't comprehend how we can talk about personal problems on TV.
"Americans carry a great conceit of the individual; we must be heard," he says. "But for people here, their reality is the desert, the great leveler of humanity.
"Life can be short, so they are very close to their humanity. They love their children, their food, and will stay up all night talking - even with [the allure of watching] TV. They are not consumed by it like we are.
"Saudis enjoy modern things, but use them and discard them when they are through.
"In America, we love our car, love our computer...," he says. "The Saudis don't understand it. They are interested in knowing you."