The Irish Catholic Bishops decided to write a pastoral document on conscience as a brief and accessible guide for Catholics. A better understanding of the word "conscience" would help to bring some clarity to contemporary public discussions and debates which often seem to be exercises in mutual incomprehension.

Those of us who would like to think that we are still middle-aged may perceive symptoms of a moral crisis. The clear certainties of our youth appear to have yielded to confusion and disillusionment. Old loyalties have come to seem naive; old heroes have revealed feet of clay.

We felt quite daring the first time a classmate persuaded us to smoke cigarettes behind the bicycle shed. Now youngsters are persuaded to use illegal drugs; they are targeted by the forces of organised crime. We can look back on our youth as an innocent time. They are bombarded by material which we and our parents would have thought incredibly explicit.

The other side of the coin is that there are signs of a moral awakening. We can claim that we are facing up to the painful implications of questions which earlier generations did not recognise or failed to address. The newspapers are full of burning moral issues, about integrity in public life, the protection of children, the environment and public health, poverty, housing, proper provision for travellers, unemployment, the treatment of refugees, arms sales and the arms race, Third World debt.

In many of the areas which dominated our moral concern in the 1950s, however, there is a new permissiveness which is increasingly willing to regard behaviour as an entirely private matter. "If people are sincere, if they believe they are entitled to act as they do, who are we to judge them? It might not be right for me, but maybe it is right for them."

Such sentiments do not ring true when we encounter discordant voices about some of the issues that dominate public discussion today. We are not inclined to be so tolerant of an industry polluting the environment, a person perpetrating what we see as an injustice, or someone proposing racist views.

And yet the same considerations apply. The people who do these things or express these views are, presumably, sincere. They believe that what they are doing is right for them. So who are we to judge them?

We are not comfortable with that argument for the obvious reason that we and other people may be affected in ways that we find unacceptable. Those effects are unacceptable irrespective of the sincerity or otherwise of the people concerned.

This points to a consideration on which our ability to live together in any human community depends. No language can function according to the principle expressed in Through the Looking Glass: "When I use a word", Humpty Dumpty said in a rather scornful tone, "it means just what I choose it to mean - neither more nor less."

Morality, like language, involves communication. When I make a free choice, I "say" a number of things. I say something about the values by which I am choosing to live and the kind of person I wish to be; I say how I regard other people, as having a dignity and rights equal to my own, or as instruments I can manipulate.

Whenever you mean one thing by an action and I perceive something different, I must be able to say, "You may be entirely sincere; you may believe that what you are doing is right, but I believe that you are mistaken." Moral behaviour would be an empty, Humpty Dumpty language unless there was some reality, some truth, to express.

There is a moral crisis if, in any area of life, however personal and private, we are losing sight of the fact that our conscience is a search for the truth about ourselves and the meaning of our actions. That truth, in the end, is not a private idiosyncrasy, it is the truth about our common humanity.

It is not enough to feel right; it is not enough to weigh carefully the consequences of our decisions. Conscience is a judgment by which we try to respond to the truth about human dignity in ourselves and in others, to the truth about the infinitely forgiving God on whom we utterly depend, to the Truth, who is Jesus, our way.

In spite of all the good things to be acknowledged, there is what Pope John Paul described as "a landmine in the foundations" of our moral consensus. That landmine is the growing acceptance that what is true for one person may be false for another, that there are areas of moral decision-making where contradictory judgments can both be true, that it does not matter what you choose to do so long as you are sincere about it.

Dr Donal Murray is the Bishop of Limerick. Conscience, a pastoral document by the Irish Bishops' Conference, is published by Veritas at £1.95