Why does the President of the United States, despite constitutional separation of church and state, so often use religious language? Why is it that presidents - no matter who is in office - so often end a speech with something like, "God bless the United States of America"? Such language is one feature of American civil religion. A civil religion is the shared religious or religion-like rhetoric, symbols, and ceremonies that help unite a society. Different societies create different civil religions. In the United States, civil religion includes theistic language that assumes a belief in God, but is non-specific in its theology. It also includes patriotic language and language espousing the professed virtues of the American people.

This chart suggests both the ubiquity and the variation historically in American civil religion. It depicts the number of religious and civil religious references in each presidential inaugural address since George Washington. Religious references include any explicit reference to God or a quotation from the Bible. Civil religious references are not explicitly religious, but fit within the broader American civil religion. These include, for example, references to the "Founding Fathers" and appeals to virtues such as liberty or equality.