Steven K. Green is the Fred H. Paulus Professor of Law and Affiliated Professor of History and Religious Studies at Willamette University, a position he accepted after serving for ten years as legal director and special counsel for Americans United for Separation of Church and State. In his new book, Separating Church and State: A History, Green charts the long legacy of an important American idea.

ECM: You write that the concept of church-state separation appears to be “on the ropes” under the Roberts Court. How so?

SKG: As a historian and a lawyer, one thing that I have found very curious is just how often the conservative members of the Supreme Court now criticize the idea of church-state separation, an idea that the Court did not create but has adopted and embraced ever since a unanimous decision back in 1947. The hostility that we are seeing from these justices seems to reflect a perspective that separation has somehow been forced upon the Court. Justice Thomas has been very critical and, as recently as January, Justice Gorsuch has referred in passing to the “so-called” separation of church and state. It’s very strange, because this is a principle that the Court has roundly endorsed over the years, but now they act like it’s some kind of an alien concept. The purpose of this book is not necessarily to get into a debate about the merits of separation, but rather to explore the bona fides of the principle as well as why it has become controversial.

ECM: What’s the origin story of church-state separation? Is it traceable directly to the Constitutional Convention, or only as far back as the Warren Court?

SKG: In this book I am very interested in the historical pedigree of the concept, and how it has evolved over time. I therefore open with some attention to the western Christian origins, dating back to the Middle Ages, when the Catholic Church was trying to free itself from the control of the Holy Roman Empire and so drew a line in the sand. St. Augustine wrote about the two cities separated by a wall, the one temporal and the other sacred. So the concept goes back to the Church doctrine of separate spheres of influence. Later it acquired an Enlightenment strain. In each case it predates the colonies, and it certainly predates the Constitution. Now, there was nothing in the Constitution initially that dealt with religious issues except for the “no religious test clause” that was put into Article 6. Separation of church and state wasn’t really debated during the Constitutional Convention, though it would come up two years later with the drafting of the First Amendment. Even then, the phrase was not explicitly used.

ECM: What is the distinction between “separation” and “disestablishment,” and why does it matter?

SKG: Disestablishment is the disentanglement of the public and private religious spheres, in terms of both regulation and support of religion. That does not necessarily imply entirely separate spheres of activity with no crossover, as separationism does. We need to keep in mind that these are not synonymous. The book does not make the claim that the majority of the Founders, who voted for disestablishment, necessarily supported complete separation of church and state. Separationism remains a very fluid concept that can have multiple meanings. It wasn’t a concept that was alien to the Founders, but I don’t claim that there was any consensus around it. There was far greater consensus around disestablishment. Even the three states that retained their colonial religious establishments—New Hampshire, Connecticut, and Massachusetts—all claimed that they did not have establishments. This was a bad word even then. So the movement toward disestablishment was well underway even before the Constitution. There was no turning back on that. But it’s different and more difficult to determine the extent to which certain of the Founders may have believed in one version of separation over another.

Read the whole thing at Religion & Politics.