If you are enjoying your breakfast coffee, this column might best be read later.

A few years ago Barbara Tuchman plunged deep into the 14th century and surfaced with fists full of startling facts, including this: "In village games, players with hands tied behind them competed to kill a cat nailed to a post by battering it to death with their heads, at the risk of cheeks ripped open or eyes scratched out by the frantic animal's claws." That vignette, although appalling, illustrates something heartening and relevant to a facet of U.S. constitutional law: human sensibilities evolve.

The evolution of standards of decency is relevant to the argument about capital punishment, which is in part an argument about the meaning of the Eighth Amendment prohibition of cruel and unusual punishments. Recently the Supreme Court refused a writ of certiorari from Jimmy Glass, who has been sentenced to die by electrocution in Louisiana. A refusal of a writ -- a refusal to review -- rarely makes news, and this one did not. But it detonated a dissent from Justice William J. Brennan.

Glass says electrocution involves "gratuitous infliction of unnecessary pain and suffering and does not comport with evolving standards of human decency." Louisiana's Supreme Court has said that his claim is without medical or scientific merit. Brennan says, as he always does in capital punishment cases: not so fast.

In 1888 New York became the first state to adopt electrocution. It did so for humanitarian reasons. In 1890 the Supreme Court authorized New York's first electrocution, making two arguments. It accepted the "historical" construction of the Eighth Amendment, arguing that electrocution is not cruel and unusual in light of contemporary norms at the time the Bill of Rights was adopted. And it said electrocution was certain to produce instantaneous and therefore painless death.

Brennan says the court has long since rejected the "historical" construction, insisting that the words "cruel and unusual" draw their meaning from "evolving standards of decency that mark the progress of a maturing society." That such standards evolve is obvious. What is far from obvious is that judges are better than elected representatives at discerning current standards of decency.

Swerving around that difficulty, Brennan adduces testimony that questions the instantaneous and painless nature of electrocution. He relentlessly piles on details about the physical effects of electrocution, which he considers the "technological equivalent of burning people at the stake." He describes eyeballs popping out, flesh burning, tendons snapping, skin rupturing, the brain reaching the temperature at which water boils, the liver still too hot to touch during autopsy.

Brennan cites various court rulings that the "cruel and unusual" clause forbids punishment that involves unnecessary pain, violence, mutilation or "lingering" death. He says electrocution involves all four and cites people he describes as "electrical scientists" who say that electrocution can cause excruciating pain of several minutes' duration. It is unclear that those scientists are qualified to make that determination, but if the question is truly open, it has a legislative, if not a constitutional, dimension.

Legislatures, more than judges, should respond to the evidence. And indeed some legislatures are uneasy. In some states, where community standards support capital punishment, legislatures are voting to abandon electrocution in favor of lethal injection, for humanitarian considerations.

The power of Brennan's argument is diminished by the fact that he will seize any stick for beating down capital punishment. But that fact about him is irrelevant to his argument, which turns on certain empirical claims that are, as yet, disputable. If established, they would establish, at most, the unconstitutionality not of capital punishment but of one way of inflicting it. Public-opinion polls confirm what the actions of state legislatures demonstrate: a substantial majority of Americans considers capital punishment compatible with civilized standards of justice.

Brennan believes what is true about electrocution would be true enough about any alternative method of execution. As Albert Camus said about the guillotine, "The man who enjoys his coffee while reading that justice has been done would spit it out at the least detail."

Perhaps. But revulsion is not an argument, and justice need not be easy to gaze at. Brennan believes he has made a case for "measured judicial consideration" of the compatibility of the Eighth Amendment and one facet of American justice. Actually, he has used a judicial instrument -- a dissent -- to demonstrate the case for, and to initiate, a public debate that should be conducted and resolved by those responsible for representing community standards of decency: elected representatives.