Kagan Is Sworn in as the Fourth Woman, and 112th Justice, on the Supreme Court

Elena Kagan was sworn in on Saturday as the 112th person, and fourth woman, to serve on the Supreme Court, continuing a generational and demographic transformation of the nation’s highest bench. In keeping with tradition, Ms. Kagan first took the constitutional oath given to a wide array of officials and then the judicial oath administered to those wearing the robe. Joined by family and friends in the Supreme Court building, she swore to “administer justice without respect to persons, and do equal right to the poor and to the rich.”

The low-key formal ceremony came two days after she was confirmed by the Senate and a day after President Obama marked her ascension with a jubilant televised celebration in the East Room of the White House. She was Mr. Obama’s second successful nominee to the court, and her approval by the Senate was taken as a jolt of validation for a White House battered by political and economic troubles.

Succeeding Justice John Paul Stevens, the court’s retiring liberal leader, Justice Kagan, 50, presumably will not drastically change the philosophical balance on the divided court. But if she were to serve until she was 90, as Justice Stevens has, she would have four decades to shape the nation’s legal architecture, long after the man who appointed her left the White House. Even a shorter tenure would give her time to leave her mark. Arguably, Justice Kagan made a mark from the moment she took the oaths on Saturday. She is the third woman on the current court, joining Justices Ruth Bader Ginsburg and Sonia Sotomayor. She is also the fifth justice born after World War II, making that group a majority, and she brings down the average age on the court to 64, from nearly 69. And she is the first person since William H. Rehnquist, 38 years ago, to join the court without experience as a judge.

If her installation added diversity in some ways, though, it reinforced the court’s lack of it in other areas. Her addition means the court now includes neither Protestants nor anyone without an Ivy League background. Justice Kagan joins two other Jewish justices and six Catholics. She is the sixth justice to have studied at Harvard Law School (although Justice Ginsburg later transferred to and graduated from Columbia Law School); the other three graduated from Yale Law School. And she is the fourth justice to have grown up in New York City.

Mr. Obama did not attend Saturday’s ceremony, but at Friday’s event he said a third woman on the court would make it “a little more inclusive, a little more representative.” He added, “It is yet another example of how our union has become more, not less, perfect over time — more open, more fair, more free.”

Afterward, Justice Kagan made no mention of that but vowed to uphold the rule of law, saying she would “work my hardest and try my best to fulfill these commitments and serve this country I love as well as I am able.”

Justice Kagan seemed to have had her sights trained on the Supreme Court for years. She served as a lawyer and domestic policy aide in the Clinton White House, was dean of Harvard Law School and, last year, was appointed by Mr. Obama as solicitor general, the government’s lawyer before the Supreme Court.

She was confirmed Thursday on a 63-to-37 Senate vote, with most Republicans opposing her, citing her lack of judicial experience and liberal views on issues like abortion, guns and gay rights.

Republicans criticized her for barring military recruiters from using a Harvard facility because of the rule banning gays and lesbians from serving openly. They also said she “would ally herself not with the constitutional liberties of all Americans, but with the big government agenda of the president who nominated her,” as Senator Jeff Sessions of Alabama, the ranking Republican on the Judiciary Committee, put it.

Saturday’s ceremony consisted of two parts. First, in the justices’ conference room with just a handful of Ms. Kagan’s relatives present, Chief Justice John G. Roberts Jr. administered the constitutional oath for federal employees swearing to “support and defend the Constitution.” Then they moved into the larger West Conference Room, where the chief justice administered the judicial oath.