But exactly what is patriotism?

"In a general way, patriotism means love of country — love of one's country, one's homeland — a very simple emotional attachment to the place where you're from," says Jack Citrin, professor of political science at the University of California-Berkeley.

"After that, agreement tends to dissolve."

Some people religiously salute the flag; some wrap themselves in the flag — literally. Others burn it and say patriotism is about protest.

"There are various ways people love the country, just as there are various ways people love their spouses or love their friends," says Thomas Cushman, a professor of sociology at Wellesley College.

Patriotism is so complex that academicians have loosely broken it down into categories, although they don't all agree on the labels:

• Devout patriotism. Unconditional loyalty to country. Also called blind patriotism because adherents will support the country no matter what, espousing the ideology, "My country, right or wrong."

• Symbolic patriotism. Attachment to symbols and rituals, such as the flag and patriotic songs.

• Constructive or critical patriotism. Belief that the best way to love one's country is with constructive criticism of the government.

Increasingly these days, disagreement leads to arguments and accusations of others being unpatriotic.

Patriotism "is something that almost everyone thinks is good," says Nolan McCarty, professor of politics and public affairs at Princeton. "So if you can attach your idea to something that is good — Mom, apple pie, patriotism — that's a particularly effective way of selling the idea.

"What's newer and more divisive is that people often take it a step further. Not only do they assert that their idea is patriotic, but they discredit other ideas by suggesting those ideas are not in the best interest of the country."

And regardless of where one sits on the political spectrum, that's troubling, says Jacob Needleman, professor of philosophy at San Francisco State University and author of "The American Soul."