WASHINGTON — Almost 20 years ago, during the Supreme Court’s winter break in 2004, Justice Antonin Scalia took a free trip on a Gulfstream jet, hitching a ride with Vice President Dick Cheney on a government plane. The two men were going duck hunting in Louisiana.

The trip ripened into a controversy, as the court had recently agreed to hear a case in which Mr. Cheney was a party. Lawyers for the other side asked Justice Scalia to disqualify himself, and he issued a combative 21-page memorandum refusing to do so.

Aspects of that memo are instructive in thinking about the lavish vacations, including travel in a private jet, that Harlan Crow, a wealthy Republican donor, has provided to Justice Clarence Thomas and his wife, Virginia, over the years, as detailed by the news organization ProPublica.

Unlike Mr. Cheney, Mr. Crow is not known to have had business before the court, so the two cases are hardly identical. But Justice Scalia’s discussion of whether the plane ride was a gift, what it was worth and whether it needed to be disclosed helps illuminate the legal standards that apply to Justice Thomas’s travels.

In his memo, Justice Scalia, who died in 2016, acknowledged that traveling on the Gulfstream was nice. “To be sure,” he wrote, “flying on the vice president’s jet was more comfortable and more convenient than flying commercially.”

But he disputed an assertion in the motion seeking his disqualification that he, and members of his family who accompanied him, had received a gift worth “thousands of dollars.”

“Our flight down cost the government nothing, since space available was the condition of our invitation,” Justice Scalia wrote. “And, though our flight down on the vice president’s plane was indeed free, since we were not returning with him we purchased (because they were least expensive) round-trip tickets that cost precisely what we would have paid if we had gone both down and back on commercial flights. In other words, none of us saved a cent by flying on the vice president’s plane.”

According to ProPublica, a nine-day trip to Indonesia supplied by Mr. Crow, including travel by private jet and yacht, would have cost Justice Thomas $500,000 had he chartered the plane and yacht himself.

Justice Scalia discussed whether his flight with Mr. Cheney had to be disclosed, concluding that “social courtesies, provided at government expense,” need not be.

“The Ethics in Government Act of 1978, which requires annual reporting of transportation provided or reimbursed, excludes from this requirement transportation provided by the United States,” he wrote.

As a general matter, though, Justice Scalia did not dispute that the law — which applies to “judicial officers,” including “the chief justice of the United States” and “the associate justices of the Supreme Court” — was binding on him.

In his 2011 year-end report on the state of the federal judiciary, Chief Justice John G. Roberts Jr. said that the constitutionality of the law was untested but that he and his colleagues obeyed it.

“Congress has directed justices and judges to comply with both financial reporting requirements and limitations on the receipt of gifts and outside earned income,” he wrote. “The court has never addressed whether Congress may impose those requirements on the Supreme Court. The justices nevertheless comply with those provisions.”

Justice Thomas did not disclose the flights on Mr. Crow’s jet. In a brief statement issued after ProPublica revealed the trips, Justice Thomas said that unnamed “colleagues and others in the judiciary” had told him that “this sort of personal hospitality from close personal friends, who did not have business before the court, was not reportable.”

He added that the Judicial Conference of the United States, the policymaking body for the federal courts, had recently issued new guidelines requiring disclosure of travel by private jet and stays in commercial properties like resorts.

“It is, of course, my intent to follow this guidance in the future,” Justice Thomas said.

In his 2004 memorandum, Justice Scalia said he could sit on the case involving Mr. Cheney because the vice president had been sued in his official capacity, adding that there was a cost to questioning the ethics of Supreme Court justices.

“While the political branches can perhaps survive the constant baseless allegations of impropriety that have become the staple of Washington reportage, this court cannot,” he wrote. “The people must have confidence in the integrity of the justices, and that cannot exist in a system that assumes them to be corruptible by the slightest friendship or favor, and in an atmosphere where the press will be eager to find foot faults.”

Justice Scalia later joined a seven-justice majority that refused to force Mr. Cheney to disclose secret documents from an energy task force.

After Justice Scalia issued his memorandum in 2004, I asked six experts on legal ethics for their reactions. One of them, James E. Moliterno, now a law professor at Washington and Lee University, focused on jokes made at the justice’s expense.

“I have received,” Justice Scalia wrote, “a good deal of embarrassing criticism and adverse publicity in connection with the matters at issue here — even to the point of becoming (as the motion cruelly but accurately states) ‘fodder for late-night comedians.’”

Twenty years later, Justice Thomas’s travels have also been a gift to a new generation of late-nights hosts.

Back in 2004, Professor Moliterno said the jokes stung for a reason. “If the standard is appearance of impropriety,” he said, “late-night comics do sometimes have a sense of how things appear to the public.”