As the few surviving photographs we have of him suggest, Emile Durkheim was by all accounts a somewhat stern man. His moral seriousness was such that his nephew, Marcel Mauss, was reportedly struck by a deep panic at almost being discovered by his uncle while in the midst of the venal pleasure of enjoying an afternoon beer outside a Parisian cafe.

Yet within Durkheim's unflinching commitment to la vie serieuse, there is a striking dichotomy. On the one hand, he was utterly committed to what he understood to be the scientific foundations of the sociological method to which he was committed. He believed that a scientific approach to understanding human life could be the basis of a new public morality. Unlike more recent attempts to understand morality through cognitive or neuro sciences though, exemplified by writers like Jonathan Haidt or Sam Harris, Durkheim's emphasis was on a social science that could understand morality in terms of the processes and structures of society. He was utterly committed to rational scholarship, describing (however inaccurately) his argument in The Elementary Forms of Religious Life in terms of an experiment, and his conclusions as confidently proven by scientific method.

At the same time, Durkheim was a man of moral passions. He was, like many others of his day, deeply exercised by the Dreyfus Affair, and the obvious miscarriage of justice meted out on a Jewish officer scapegoated by his military superiors for a crime he did not commit. At the height of this affair, Durkheim found himself drawn into a public war of words with a conservative "anti-Dreyfusard" polemicist, Ferdinand Bruntière. In an enraged response to Emile Zola's J'Accuse, Bruntière had disparaged those liberal intellectuals and artists who dared to challenge the moral authority of the army on the basis of a regard for the individual that he considered "the great sickness of the present time". In an article responding to Bruntière, Durkheim wrote:

"The human person, whose definition serves as the touchstone according to which good must be distinguished from evil, is considered as sacred, in what one might call the ritual sense of the word. It has something of that transcendental majesty which the churches of all times have given to their Gods. It is conceived as being invested with that mysterious property which creates an empty space around holy objects, which keeps them away from profane contacts … Whoever makes an attempt on a man's life, on a man's liberty, on a man's honour inspires us with a feeling of horror in every way analogous to that which the believer experiences when he sees his idol profaned."

Here, then, is a curious tension. On the one hand, Durkheim shrouded his work with claims of scientific authority. Yet at the same time, his heart beat with moral passions that could be expressed in most articulate form through a poetic language of the sacred.

This tension goes to the heart of Durkheim's project of developing a sociological understanding of the sacred. On one hand, the aim of this project is to develop a more rational, reflexive understanding of the nature and influence of the sacred on social life. In doing so, it offers the potential for us ask where these moral certainties have come from, and what their effects on society are. Yet while promising the possibility of greater rational detachment, we can never really be freed from moral passions if we are to remain genuinely social, or indeed ethical, beings. We might, for example, be able to understand rationally the historical conditions under which the care of children has come to have sacred significance, and how this creates its own negative consequences from unwieldy regulations over contact with children to the ritual scapegoating of over-stretched social work professionals. But, however clear our rational gaze on the origins and implications of this particular form of the sacred might be, we would still feel less than human if we saw an image of an abused and neglected child and were not deeply moved by it. Such sentiment seems necessary to motivate serious collective action against that which morally troubles us.

This dichotomy is not, ultimately, a problem to be solved, however, but a tension to be lived through. There is no real prospect of social life being organised around purely rational knowledge – however appealing that Enlightenment ideal might be to some people. Our knowledge of our social relations is always as much, if not more, felt than thought about. But equally, a society based on uncritical moral passion, or in which sacred passion forms an unholy and unchallengeable alliance with political power, has repeatedly been shown through history to have lethal consequences. We must learn to live with a creative movement between rational reflection and moral passion – even if that rationality may at times feel like it profanes our deepest sacred sentiments. For without both moral sense and moral sensibility, we will never manage successfully the always flawed project of managing ethically a shared, collective life.