Very rarely do sitting Supreme Court Justices pen manifestos declaring their views on how judges should make decisions. One exception was Antonin Scalia’s 1997 book “A Matter of Interpretation: Federal Courts and the Law,” in which he defended an originalist interpretation of the Constitution and urged judges to confine themselves to the literal meaning of legal texts rather than pursue abstract or legislative goals.

Stephen Breyer’s new book, “Active Liberty” (Alfred A. Knopf, 176 pages, $21), is the evolutionists’ rejoinder. In this slim volume, Justice Breyer argues that judges sometimes need to go beyond the literal meaning of constitutional provisions in order to pursue the broader, more general goals those provisions were intended to advance.

Chief among Justice Breyer’s constitutional goals is the creation of a more vibrant and participatory democratic culture in a nation where public ignorance and voter apathy are at all-time highs. He explains this emphasis on democracy by employing the 19thcentury political philosopher Benjamin Constant’s distinction between the liberty of the moderns – essentially individual rights – and the liberty of the ancients – the right to self-government.

Justice Breyer agrees with Constant’s contention that we should “learn to combine the two together” and worries that in recent years the courts have neglected ancient liberty in favor of modern. “My thesis is that courts should take greater account of the Constitution’s democratic nature when they interpret constitutional and statutory texts,” he writes. Just as the Constitution as a whole indicates a democratic purpose, individual constitutional provisions may also have purposes beyond the mere text of their clauses.

For instance, Justice Breyer thinks that the religious freedom clauses of the First Amendment are aimed at avoiding divisiveness and social conflict based on religion. So a judge considering whether state-funded vouchers could be used in religious schools would not attempt to look for a ruling based on the text of the First Amendment. Instead, he would ask whether the consequences of deciding the case one way or the other will be likely to create religious discord in contemporary society.

In a recently decided case in which the majority determined that vouchers for parochial schools pass constitutional muster, Mr. Breyer disagreed. “Nineteenth- and twentieth-century immigration has produced a nation with fifty or more different religions,” he writes here. “And that fact made the risk of ‘social conflict’ far more serious after the Civil War and in twentieth-century America than the Framers, with their eighteenth-century experience, might have anticipated.” Thus the First Amendment should be understood as barring vouchers, even if that means giving the amendment a far broader reading than the Framers would have thought appropriate.

Justice Breyer is well aware that his way of judging has its critics. The chief objection is that it fails to provide adequate safeguards against judicial abuse. The open-ended pursuit of abstract constitutional purposes not directly tied to the actual words of the Constitution makes it easier for judges to substitute their own views for constitutional requirements.

What’s more, letting unelected, life tenured judges slip loose of the hold of legal texts amounts to an expansion of their power over our country, which seems dangerously undemocratic. If the overarching goal of our Constitution is to create a more democratic America, a legal doctrine that enhances the authority of judges seems particular inapt.

Justice Breyer insists that the practice of judicial modesty and respect for precedent will often prevent judges from making radical changes in the law, while at the same time allowing that a court following his approach may at times engage in radicalism. His chief example of desirable radicalism is Brown v. Board of Education, the decision that declared school segregation unconstitutional.

The problem with the Brown example is that its strength arises from the unique injustice of racial segregation. It’s impossible to think of anything in American society that would justify a return to Brown-style judicial radicalism, and it is dangerous to arm judges with a philosophy of decision-making that leaves them free to be radical even in the absence of such justification. Similarly, it took a Civil War to end slavery, but that’s no reason to dispatch the military at all signs of conflict.

Helped along by Justice Breyer’s clear and personal writing style, “Active Liberty” is the best guide we have to the more liberal style of legal decision-making. For anyone wanting to know what is at stake in the Roberts hearings, it is essential reading. Liberals hoping that Justice Breyer would provide a conclusive argument for his approach to the law, however, will simply have to keep hoping.

Mr. Carney is an attorney in New York.