The senseless murder of a young woman in Bristol over Christmas raises important questions about the nature of evil. As morality is about this very issue – the nature and origins of good and evil – it is worth asking the philosophical question: what is evil?

To Aquinas and natural law theorists evil is a failure to recognise and follow our primary purposes which reflect the very essence of what it is to be human. One of these primary purposes or precepts is the preservation of life. We have been given knowledge of good and evil and this is also observable in the way reasonable people behave. The murderer of Jo Yeates must therefore in some way have subverted reason – found some sick rationale for an appalling act that is so clearly against reason and nature.

Kant saw evil as irrationality too, but his rationality is a priori, based on the principle of universalisability – that we should only act in a way that we can apply to all people in relevantly similar circumstances. We cannot reasonably conceive of a world where murdering was acceptable, because to do so would mean that it’s fine to murder me or to murder my loved ones. Evil is therefore a contradiction in nature, according to Kant, but by “nature” he means something different to the natural law theorists.

Mill and Hume believe something slightly different again. The primary motive for being good is sympathy for our fellow human beings. We are aware that evil produces much misery and suffering, and we should try to keep such misery as low as we possibly can. According to Mill, Jesus’ golden rule represents the pinnacle of utilitarian thinking “do to others as you would have them do to you”, which is interesting because this is often thought of as the essence of Kantian ethics (discuss!).

The Bible has a number of ways of describing evil. Evil is a falling short of God’s standards and purposes (back to natural law) as an arrow might fall short of a target. But evil is also disobedience to the divine will as revealed for example in the ten commandments (hence we talk of “divine command theory”). And most interestingly for this appalling tragedy, we can be possessed by evil – the demon-possessed man in Mark 5 is cutting and destroying himself, out of control, possessed by a strange power and compulsion that isolates and will ultimately kill.

And here this case touches all of us. We need to love ourselves before we can love others. We need to identify any strange and destructive compulsions we may have and find ways of facing them, perhaps with help from another person. We need to grasp our own humanity and make sure, in line with the thinking of the virtue ethicists, what relationships will make me flourish, to transcend all our capabilities of destroying ourselves and others, most horribly demonstrated in this senseless crime.