By bringing the persistence of the sacred in the modern world more clearly into view, Durkheim's work leaves us with one final question. Do we really need the sacred? If we think about various horrors of the past century – from mass starvation in Stalin's Russia, the machinery of death of the Nazi concentration camps or the genocidal killing fields of Cambodia and Rwanda – we see acts that were justified by their perpetrators in terms of purifying society from evil. The sacred can form a basis for moral certainty which, when allied with unchecked political power, can lead to all manner of collective violence. Isn't the persistence of such sacred horrors an affront to the Enlightenment ideal of a society based on the rational pursuit of truth and happiness?

This question becomes redundant, though, if we think that the sacred is an inherent part of human life. This was certainly Durkheim's view. In The Elementary Forms, he argued that people experienced a fundamental need to create and experience the sacred because of their innate sense of being part of a greater whole. This sense of something greater was not, argued Durkheim, an intuition of the existence of God or some mystical cosmic unity. It was the experience of being part of the greater whole of society, something that all human beings as inherently social creatures share.

Social origins of the sacred have also been claimed, more recently, by writers like Scott Atran and Jonathan Haidt who argue that the collective experience of the sacred was an important adaptation of the crucial human capacity for co-operative social action. Groups who were able to form a strong moral ethos focused around sacred symbols and sentiments were more able to act collaboratively and thus successfully in vital tasks like hunting or the protection of children. As human societies grew more sophisticated, sacred symbols and rituals continued to perform an important role in binding ever larger populations together in a sense of shared meaning and identity. From this evolutionary perspective, then, the sacred may have a terrible potential for unleashing violence against those considered profane. But it has also played an important role in making possible ever more complex forms of social collaboration on which human civilisation depends.

These accounts of the origins of the sacred may help us to understand its roots in deep pre-history, but are less useful for understanding the role that the sacred plays in modern society. When Durkheim, Atran and Haidt write about the function of the sacred in binding social groups together, our minds are drawn to the image of a tribe sharing a moral ethos around a single sacred focus. But we know from our discussion in this series so far that western modernity is shaped by an array of sacred forms (including the nation and humanity) which flow through our individual moral sentiments in complex and, sometimes, contradictory ways. Haidt himself, for example, writes well about the bemusement he felt as a political liberal when, in the immediate aftermath of 9/11, he felt a deep moral compulsion to put a bumper sticker of the American flag on his car.

Modern societies are not single tribes organised around a shared sacred vision. Nor are they, for the most part, made up of competing moral tribes, with their own distinct visions of the sacred. They are held together primarily by a range of mundane ties and ways of living that help us to know how to exist sociably with each other. But alongside this is a flow of sacred images and stories which sometimes catch the imagination and passions of a particular audience, and often do not.

How do we make sense of the sacred in the light of this? If the sacred originally emerged as a way of creating a shared moral ethos in groups, modernity has broken it from this simple evolutionary function. We no longer live in the type of simple tribes, focused around sacred rituals, about which Durkheim wrote in The Elementary Forms. But the sacred and the profane still remain as relevant as ever. They continue to circulate through social life, creating temporary moral alliances, often activated in response to a particular profane threat, which continue to give people a sense of the fundamental moral boundaries of what it means to be human. These sacred visions may be fleeting, but still can exert considerable power while their influence lasts. The sacred and the profane will always be with us as long as we need to communicate together about the moral foundations of social life. We cannot imagine a society in which this need is not present. And so the enduring challenge for us is not to dream of a world beyond the sacred, but to understand how we can lessen the harm that is done in its name. If we can find rigorous ways of undertaking this task, we will have carried forward the spirit of what Durkheim understood about what it means for us to believe.