Experience alone should allay anxieties that one need tote around a Bible — or, for that matter, a Quran or a Bhagavad Gita — to know right from wrong. And even accepting the premise of the sometime conversation-stopping “it’s not in the Bible” fatwa, just to know a specific precept may be found in the Bible is by no means a guarantee it will be heard, heeded or adhered to. The foundations of morality lie deeper than the agents of their transmission. According to Catholic teaching, reason and revelation both testify to their discoverability in the core of every human being.

Not a few Catholics, self-conscious as they may be of a certain ineptitude in citing chapter and verse, express surprise to learn that Catholic moral teaching is not primarily an exercise in assembling quotes from Scripture. St. Paul himself observed that even those (the Gentiles) who do not know the Mosaic Law observe its prescriptions by nature “written in their hearts (and) their conscience also bears witness and their conflicting thoughts accuse or even defend them” (Romans 2:14-15). Our most respected theologians have long recognized that the moral principles which humanize humanity are found within the nature of the human person itself.

Call it “natural law,” if you will, we might prefer the term “right reason” (“recta ratio”) used by St. Thomas since it recognizes implicitly that both nature and reason can be twisted or blinded by our fallen state. Nevertheless, it is possible, though not always easy, to arrive at universally valid moral principles for all who share our human nature. If that is so, then there is hope for finding common moral ground, even for those between whom their religious convictions seem to put enmity.

Yet another wave of violence in the name of religion has inundated the world in recent weeks. Much — if not most — of the media have focused on so-called enraged “religious feelings” or sensitivities. “Nothing, in fact, can justify the activity of terrorist organizations and homicidal violence,” the Holy See has reiterated, which would apparently include hurt feelings. Indeed our confidence in the soundness of our beliefs and principles may be in direct proportion to our willingness and ability to endure the taunts of those who disdain them. Violence is always a failure of moral courage, a desperate admission of defeat, a choice of raw power when the persuasive force of the principle itself is found (or feared) wanting.

Both the First Amendment to the U.S. Constitution and the teaching of the Church, articulated in Dignitatis Humanae of Vatican II, affirm strongly the right of religious liberty. Tellingly, the foundation of this principle — what enables both church and state, the religious and the secular to arrive at common ground — is an awareness and appreciation of certain self-evident truths that are written in the nature of humanity itself. We do not need “proof” from Scripture or science that stealing, murder and racism are wrong. No one wants to be the object of any of these transgressions and, in good reason, no one has the right to perpetrate them.

So also, the freedom to speak in the name of religious convictions, however inconvenient or offensive its exercise might be, is rooted in the very nature of what it is to be human. It is one of those principles that, if respected and adhered to, humanizes humanity. It acts, quite frankly, as a life-preserver for everyone, a barrier against self-cannibalization, which is where violence ultimately leads.

A great advantage of “natural law” (understood as “right reason”) as a foundation for moral knowledge and discourse is that it offers a language that can be understood and spoken by people of different faiths and traditions. It is, therefore, a secular rationale for civil law that is perfectly compatible with many religious principles. It acknowledges that moral truth is not the sole possession of one religious hierarchy or orthodoxy and that it is accessible to all by virtue of our humanity.