At what level does stealing constitute a mortal sin? The answer as I write is £155.02. I say this with confidence because the good Jesuits taught me, in 1944, that £5 constituted “grave matter”, and so potentially a mortal sin. It may even have altered a penny or two by the time you read this. Aren’t we lucky?

A combination of the modern Catechism and the thoughts of leading moral theologians enable us to measure immediately the moral status of any act we have committed or are proposing to commit.

In these days of the smartphone every Catholic should have an app which will not only assess gravity but will indicate a proper penance. No doubt, as artificial intelligence advances, an app will also give us absolution once we have ticked the box confirming our firm purpose of amendment. We must hope that St Peter has a good connection to the internet.

But I am being serious. Behind me as I write are several volumes on Catholic moral matters but very little on the formation of conscience. Perhaps I don’t need it: if the answer is always to be found at the back of a book, why look for a different answer? Yet the deep theology of the moral life tells us that we stand or fall by our response to what we recognise to be evil or good. It is really rather important.

Let’s see what a secular situation might tell us. Imagine that you take your child to a doctor because he suffers from bedwetting. Your doctor concludes that the child has psychological anxieties and should be referred to a psychoanalysis expert. But your own research tells you that enuresis is best cured by behavioural methods. Which authority do you follow: the doctor or your own judgment? The answer must lie in which you judge to be in your child’s best interests. It is quite proper, of course, to choose the recognised authority if we think it to be more likely to be right than us, but vice versa if we do not.

Is this a parallel for moral questions? Here, the authority is likely to be the Church’s moral law. There is no doubt that this has authority in its moral teaching, but changing situations or better understandings have led to developments from time to time. An interesting example was the elevation of the seriousness of abortion when science, via the microscope, demonstrated the radical unity of the embryo from conception onwards. Currently the argument concerns whether an individual in a technically adulterous marriage can ever rightly receive the Eucharist.

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