“The legitimate powers of government extend to such acts only as are injurious to others,” Thomas Jefferson wrote in his Notes on the State of Virginia. “But it does me no injury for my neighbor to say there are twenty gods, or no God. It neither picks my pocket nor breaks my leg.” Jefferson's words express a legalistic conception of religion as rooted in individual conscience. Religion expresses an understanding of life beyond that reality evident in the material world. It answers questions common to humanity throughout time: Where does life come from? Is there a grand purpose for life on earth? Is there life after death? Jefferson implicitly argues that the answers to these questions are unknowable. Individuals can therefore form various answers to them, each of which constitutes a personal truth to its holder, but is of little consequence to anyone else. Conversely, many Americans before, during, and after Jefferson's lifetime have conceived of the answers to these questions as revealed by God in the Bible. For them, the text of the Bible provides an unerring and public truth that can and must serve as the basis for society.

However, Jefferson's words address far more than a form of religious belief; they also outline a conception of society in which government is confined to acting within a circumscribed public sphere. The need to limit the scope and power of the public sphere derived from a recognition of rights as essential aspects of human existence; to deny or limit humanity in its enjoyment of rights constituted a prevention of human progress and happiness. Therefore, the founders created a private sphere in which people remained free to pursue their rights and a separate public sphere with limited authority to address the needs of civil society, the most significant of which was the protection of rights from injury. Jefferson's words place religion in that private sphere and therefore beyond the scope of government.

The humanistic philosophy popular during the late 1700s celebrated humanity's autonomy, reason, rationality, and ultimate ability to improve itself and the world around it. In the aftermath of the Revolution, liberals used humanist values to redesign the laws and institutions of the new republic, values that recognized the novel – for the eighteenth century – distinction between public and private realms.