After two Supreme Court confirmation hearings in quick succession, Americans now know more about the legal principle of stare decisis than perhaps they ever wanted to. Yet according to three of its own members, the Supreme Court itself may need a refresher course in the legal doctrine that courts ought to have great respect for their own precedents for the sake judicial and societal stability. By a vote of six to three, the Court yesterday struck down the Bush administration’s attempt to block Oregon’s assisted suicide law, but in the course of doing so the justices ignored an interpretation of the relevant federal statute that they had promulgated just seven months ago.

The case decided yesterday, Gonzales v. Oregon, hinged on the Controlled Substances Act, passed by Congress in 1970 to regulate medications. The law permits the federal Justice Department to regulate prescriptions for a wide array of powerful drugs that are prone to abuse. In 2001, Attorney General Ashcroft issued a rule stating that Oregon’s assisted suicide law, which permits doctors to prescribe lethal quantities of medicine to terminally ill patients, ran afoul of the federal act. Yesterday the Court opted to disallow that interpretation.

The three dissenters – Justices Scalia and Thomas and Chief Justice Roberts – quote from a regulation developed in 1971 to implement the CSA. It requires the attorney general to consider whether a “legitimate medical purpose” exists for prescribing a certain medication. The justices then argue that Mr. Ashcroft’s threat to strip Oregon doctors of prescribing privileges if they helped a patient kill himself is perfectly in keeping with the attorney general’s rights and responsibilities under the law. Considering that the administration presented evidence that a long line of doctors from Hippocrates to the American Medical Association have rejected the idea of physician-assisted suicide, it struck the dissenters – as it strikes us – that Oregon’s law does not serve a “legitimate medical purpose.”

Justice Scalia, writing for the trio, also appealed to stare decisis in his dissent, writing: “The prohibition or deterrence of assisted suicide is certainly not among the enumerated powers conferred on the United States by the Constitution. [But] from an early time in our national history, the Federal Government has used its enumerated powers, such as its power to regulate interstate commerce, for the pur pose of protecting public morality. Unless we are to repudiate a long and well-established principle of our jurisprudence, using the federal commerce power to prevent assisted suicide is unquestionably permissible. The question before us is not whether Congress can do this, or even whether Congress should do this; but simply whether Congress has done this in the CSA.”

Justice Thomas offered his own addendum to the dissent when he noted that yesterday’s ruling is directly at odds with the Court’s own interpretation of the same rule barely seven months ago, when it struck down a medical marijuana law in California. In that case, Gonzales v. Raich, the Court ruled that the CSA allowed the administration to prohibit the intrastate commerce in marijuana for medical use, even though such intrastate use would appear to steer clear of any federal interest. The Court has now apparently completely reversed itself, ruling that precisely the same section of the CSA it thought justified federal prohibitions on intrastate drug use also forbids federal prohibitions on any drug use.

Quite apart from the effects of yesterday’s ruling in respect of the assisted suicide law that was under debate, the decision offers much to reflect on as the Senate prepares to vote on the nomination of Judge Samuel Alito to replace Justice O’Connor, often described as a “swing vote” on the court. During the course of Judge Alito’s hearings last week, senators devoted a lot of time to quizzing him on his views of the importance of stare decisis, in the hope that they could discern whether he would uphold the abortion rights manufactured by the Court in Roe v. Wade. Senate Democrats also expressed concern that Judge Alito would be more in the mold of Justices Thomas and Scalia than that of Justice O’Connor.

Yet if adherence to the principle of stare decisis is the standard, those senators would be better off with a Thomas or Scalia. Both those justices actually bowed to stare decisis. They opposed the application of the federal law in the California case but have reversed course in this case, partly out of a belief that the Oregon law is not strictly intrastate, and partly out of respect even for a decision with which they did not agree when it was originally issued. Justice O’Connor, meanwhile, has abetted a flip-flop on the Court. So as they prepare to vote on Judge Alito, Senators have a case study in which kind of judicial temperament actually respects precedent.