In the 16th century, two celebrated spiritual leaders, Martin Luther and St. Thomas More, stood on opposite sides of the religious debates of their day. Ironically, they took their stand on the same principle: an appeal to conscience.  

Luther died outside the Catholic Church because he claimed that his conscience compelled him to oppose the Church. More died a martyr because he insisted that his conscience forbade him to oppose the Church.

Today, the cry to stand on conscience, especially with regard to socially contentious issues, is heard more and more among Catholics and others as well. Yet just as it was in the time of Luther and More, the conclusions drawn according to individual conscience are often contradictory. How is it, then, that trusting one's conscience seems both perennially essential and dangerously unreliable?

Consider this analogy. I'm 6 feet 4 inches in height. Most people consider me tall, but in my mind's eye I'm just average height. In fact, whenever I encounter others of my height, I think of them as taller than I am.

For most of my life, you see, my normal line of vision has tilted down as I look into the faces of family and friends. What seems, then, to be "level" or "normal" in my mind is skewed slightly downward.

My perception of height is thus not objectively accurate, but rather subjective, relative to my experience. If I had spent my life with mostly taller people or mostly shorter people, I would probably have become accustomed either way to think of myself, in my mind's eye, as their height.

Given this situation, if I were to stand before a large mirror alongside others, I'd be surprised at what appears there. No doubt I would then look around for a reliable measuring instrument, some kind of yardstick, to determine accurately how my height compares objectively to that of the others. Only then could I correct that warped lifelong perception of myself and others.

In a similar way, the perception of right and wrong that we call our conscience can become untrustworthy. Over the years, it tends to adjust to the world around us, in ways to which we are dangerously blind. Sometimes our conscience bends to be more like those whom we admire or who admire us. Sometimes it bends away from those whom we despise or who despise us.

Either way, our conscience is skewed in ways we don't recognize. Scripture recognizes this problem when it speaks of consciences that are "weak,""wounded,""branded,""tainted" (see 1 Cor 8:7-12; 1 Tm 4:2; Ti 1:15).

So how do we gain a trustworthy conscience, a vision of right and wrong that is accurate? Most people are unwilling to examine and correct their consciences until they become aware, through direct confrontation with another person's conscience or some other "Aha!" experience, that "there's something wrong with this picture!" Such an experience is like standing before the mirror.

Having recognized the problem, we must regularly examine and form our conscience by using a reliable moral "yardstick"- an objective means of measuring what is right and wrong. But practically speaking, what kind of yardstick is available?

Luther claimed that we must use Scripture alone to form conscience. But we need only observe the chaos of Christian opinions on critical moral issues to see that Luther's sola Scriptura principle has proven perpetually untrustworthy as a means of forming conscience. Merely private scriptural interpretation is simply too subjective.

Others say that the best way to form conscience is to ask "WWJD?" or "What would Jesus do?" Yet this approach can be just as subjective and shaky as sola Scriptura. We should ask instead, "What did Jesus do?"What did He do to provide us with an objective means to measure truth and form a faithful conscience?

The answer, of course, is that He gave us as a trustworthy yardstick "the church of the living God, the pillar and foundation of truth" (1 Tm 3:15). If we study and embrace the Church's precepts, and all the authoritative moral teachings of the Church, we'll form a conscience on which we can confidently take our stand.

Marcus C. Grodi is host of the popular EWTN program "The Journey Home" and president of the Coming Home Network International. Contact him at mgrodi@osv.com.