Americans who watched the vice presidential debate Thursday night saw a spirited and intriguing exercise that added to voters' knowledge about both candidates.

The biggest surprise of the evening may be that Alaska Gov. Sarah L. Palin, relatively new to national politics, made no major mistakes and gave no ground in debate. Aggressive in defending the policies of the Republican ticket and the record of GOP presidential nominee John McCain, she was equally vigorous in attacking his Democratic opponent Sen. Barack Obama.

Sen. Joseph R. Biden Jr., D-Del., is known for his fiery temperament and occasional gaffes, but he showed neither tendency during the 90-minute debate moderated well by Gwen Ifill of PBS. Instead, Mr. Biden demonstrated his command of policy with his answers on the economy, the wars in Iraq and Afghanistan, taxation and a host of other issues visited.

It was truly a vice presidential debate in that both participants criticized their presidential rivals more than they did each other. Throughout the evening, Mr. Biden argued that a McCain presidency would continue President Bush's policies and Gov. Palin sought to rebut that claim by stressing the word "maverick" in describing Sen. McCain.

Both candidates debated sharply, but neither delivered a knockout blow. While Mr. Biden said, "The economic policies of the last eight years are the worst economic policy we've ever had," Gov. Palin praised Mr. McCain's call for stronger oversight of mortgage giant Fannie Mae in 2006. Sen. Biden blamed the financial crisis on Republican calls for deregulation, including Sen. McCain's.

Discussions of the war in Iraq were intensified by the fact that each candidate has a son deployed there or about to be. Defending Democrats' plan to withdraw U.S. combat troops in 16 months, Sen. Biden said, "For John McCain there is no end in sight. Fundamental difference. We will end this war." To which Gov. Palin replied, "Your plan is a white flag of surrender. It is not what our troops need to hear."

At times adapting answers to her knowledge of energy and other issues, Gov. Palin said: "I may not answer the questions the moderator wants to hear, but I'm going to talk straight to the American people and let them know my track record."

Challenging Mr. Biden's record on the Iraq war, she said: "It's so obvious that I'm a Washington outsider. You're the one who says as so many politicians do, I was for it before I was against it."

Mr. Biden left no doubt he is qualified to step into the presidency if needed. Gov. Palin was forward-looking and articulated her philosophy of government. Both sought to connect with ordinary Americans in their own way.

Neither candidate harmed their party's cause. The discussion revealed the contrast between the two candidates. Though sharp, the debate was cordial — and well worth watching.