The execution of Yakub Memon for his alleged part in the 1993 Mumbai bombings invites us to revisit the vexed issue of capital punishment. Few topics incite such moral passion and controversy.

The world’s religious communities are divided on the death penalty. Despite a seemingly unambiguous commitment to non-violence (or “Ahimsa”) in both Hinduism and Buddhism, scholars within those traditions continue to debate the permissibility of lethal punishment. The Old Testament enjoins us to take an “eye for an eye” – the principle of lex talionis – while the New Testament exhorts us to “turn the other cheek”. And while Islam is generally regarded as compatible with the death penalty, the Qur'an’s emphasis on forgiveness suggests that Muslims should sometimes respond to evil with mercy, not retaliation.

While many European countries urge an ethic of rehabilitation in their criminal justice systems, many jurisdictions in the United States stand firmly in favour of capital punishment for serious crimes. Even a federal jury in Massachusetts, a liberal bastion, recently doled out the death penalty to the sole surviving perpetrator of the Boston marathon bombing. And while the United Kingdom abandoned the death penalty in 1964 – the year of the last executions – nearly half of the British public favours a reintroduction of it (though that figure has been dropping steadily).

We will not make progress in the public debate about the death penalty unless we realise that it is only one element in a much bigger controversy: about the point of punishment itself. As The Conversation invites us to rethink the death penalty over the next few weeks, we must not conduct this discussion in a vacuum. Before you ask yourself whether we should have the death penalty, consider: why hand out any punishments at all? Considering the three main families in the philosophy of punishment can help us organise our conversation.

Retribution

“Bad guys deserve to suffer.” This is a blunt slogan, but it captures the essence of a deeply familiar notion: people who have committed culpable wrongs deserve their lives to go worse as a result. Why do they deserve it? Perhaps because it’s not fair for the lives of wrongdoers to go well when the lives of the innocent have gone poorly – punishment levels the playing field. Whatever the reason, “retributivists” – those who believe in retribution – argue that the punishment of criminals isintrinsically valuable; it is valuable in and of itself, rather than valuable because of its good consequences (for example, preventing future crime).

Even if punishing murderers and thieves had no effect on reducing the overall crime rate, retributivists tend to think it’s still the right thing to do. Retributivists also think that the severity of punishment should match the severity of the crime. So, just as it is wrong to over-punish someone (executing someone for stealing a pair of shoes), it can be wrong to under-punish someone (giving him a community service order for murder).

If you are a retributivist, you might support the death penalty because you think that certain or all murderers (and perhaps other criminals) deserve to suffer death for their crimes. Depending on how you think about death, however, you might oppose the death penalty on the grounds that it is disproportionately harsh – perhaps you think that no matter what someone has done, she does not deserve to die for it.

On the other hand you might oppose the death penalty on the grounds that it is disproportionately light. Many people who opposed the recent death sentence for the Boston bomber did so on the grounds that life in a maximum-security prison would be a worse punishment – and so more fitting – than death.

Deterrence

“Criminals should be punished so that they and others will be less likely to commit crime in the future, making everybody safer.” Many people criticise retributivism on the grounds that it is nothing but a pointless quest for barbaric revenge.

Inflicting suffering on human beings, if it is to be morally justified, must instead have a forward-looking purpose: protecting the innocent from harm. If this sounds sensible to you, you probably believe the point of punishment is not retribution, but rather deterrence.

The idea here is familiar enough: people face temptations to break just laws; the demands of morality and the demands of rational self-interest sometimes seem to diverge. Threats of punishment realign those demands by making it irrational for self-interested individuals to break the law.

If you are a defender of deterrence, you must answer two questions about capital punishment before determining where you stand. The first is empirical: a question about real-world facts. Does the threat of the death penalty actually deter people from committing heinous crimes to a greater extent than the threat of life imprisonment?

The second question is moral. Even if the death penalty deterred crime more successfully than life imprisonment, that doesn’t necessarily mean it would be justified. After all, imagine if we threatened execution for all crimes, including minor traffic violations, theft, and tax fraud.

Doing so would surely slash the crime rate, yet most people would judge it to be wrong. Deterrence theorists tend to defend some upper limit on the harshness of punishment – and it may be that death simply goes beyond what the government is ever permitted to threaten.

Reform

“Punishment communicates to criminals that what they have done is wrong, and gives them an opportunity to apologise and reform.” There are many different variants of this view: educative, communicative, rehabilitative – and there are important differences between them. But the basic idea is that punishment should make the wrongdoer understand what he or she has done wrong and inspire her to repent and reform.

Whatever version of this view one supports, its implication for the death penalty is reasonably clear. What is the point of a criminal reforming herself as she prepares for the execution chamber?

To be sure, many people try to mix and match different elements of these three broad views, though such mixed theories tend to be unhelpfully ad hoc and can offer conflicting guidance. Far better, to my mind, to plant one’s flag clearly and answer the question: which view should have priority in our thinking about punishment?

Then, and only then, can we proceed to think about the justice (or lack thereof) of governments who kill their citizens.

This article was originally published on The Conversation.