There are no atheists in foxholes, the old saying goes. Back in the 1950s, when the philosopher Alvin Plantinga was getting his start, there were scarcely more religious believers in academic philosophy departments.

Growing up among Dutch Calvinist immigrants in the Midwest, Mr. Plantinga was used to intense theological debate. But when he arrived at Harvard as an undergraduate, he was startled to find equal intensity marshaled in favor of the argument that God didn’t exist, when classmates and teachers found the question worth arguing about.

Had he not transferred to Calvin College, the Christian Reformed liberal arts college in Grand Rapids, Mich., where his father taught psychology, Mr. Plantinga wrote in a 1993 essay, he doubted that he “would have remained a Christian at all; certainly Christianity or theism would not have been the focal point of my adult intellectual life.”

But he did return, and the larger world of philosophy has been quite different as a result. From Calvin, and later from the University of Notre Dame, Mr. Plantinga has led a movement of unapologetically Christian philosophers who, if they haven’t succeeded in persuading their still overwhelmingly unbelieving colleagues, have at least made theism philosophically respectable.