It worried me that Prince George’s new school apparently discourages its pupils from having a best friend. Now that the news of his first day has been broadcast around the world, the reported policy of Thomas’s Battersea might be taken as a gold standard or best practice. But I think it’s profoundly mistaken.

To want a best friend is both natural and good. That’s been noted ever since Aristotle wrote about what makes for a flourishing life in his Nicomachean Ethics. Friendship was central. He concluded that a person may have everything else that life can offer – money, family, purpose, values – but that they would feel they lacked something essential if they hadn’t, at some point, experienced the great joy of soulmateship.

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He realised that human beings are social creatures. We’re people of the polis. We do well when we live well together. Friendship is a crucial part of that, he continued, because it’s in the context of intimate friendships that we best learn what it is to attend to others, not only ourselves. This care can become a habit that spills out in ever widening circles to extend across the community.

It is, therefore, wrong to think that forbidding best friends prevents playground bullying and loneliness. If anything, it could promote the opposite. How else can individuals learn the tremendous value of reaching out, of acting kindly?

The fear that close friendships work against school happiness is, probably, based on an ill-defined intuition. As is commonly observed, one way to seal an effective friendship is to forge a common enemy. Best friends may do that. But animosity does not prop up faux-amity for long. Far better is to educate children about the nature of friendship. It’ll be good for them and others.

This takes us to the deeper reason that Aristotle felt soulmateship to be fundamental to humans. We make two types of friends in life, he concluded. The more usual are those we form because we share something in common. Work friends would be the classic case nowadays. But such friendships are limited. They depend upon what’s shared. If that goes, the friendship founders. It’s why work friends who bump into each other out of the office feel awkward and embarrassed, head down, earbuds in. What are they going to talk about? The chances are they will default to work – and who wants that at the weekend?

The less common type of friendship is also more valuable. It is the kind that doesn’t depend upon anything shared, though much will be shared. Instead, these friends know and love each other for who they are in themselves. In some moments they become one soul in two bodies, another self to each other. Together they can withstand the pains of life. They reflect one another, and so learn from each other.

In some moments friends become one soul in two bodies, another self to each other

We don’t always have such a best friend or soulmate, Aristotle said. But to taste it just once is to know that you have tasted something of the very best that life can offer.

The idea that best friends are damaging does have another significant root: it arises in Christian monasticism. The founders of this tradition often advised monks and nuns not to form “particular friendships”. But at heart, they did so for theological reasons. The monastic calling is to cultivate ascetic practices that help direct all of the soul’s desire towards God. In this context, friendship is a distraction. But note: monasticism is a vocation – by definition it is not meant for everyone. Another strand in the Christian tradition teaches that friendship is an excellent school for living; it’s the love within which many learn of the love of God.

To lose the context, and write a ban on particular friendships into the rule book of an entire school, is to turn a means into an end: the aim may be to prevent bullying or hurt feelings, but too much good is jettisoned along with it. It’s another reason that frowning upon best friends is risky, even dangerous.

• Mark Vernon is a psychotherapist, writer and teacher, with a particular interest in ancient philosophy