From Rosalind and Celia, coupled ‘like Juno’s swans’ in amity until exile to the forest of Arden places new possibilities in their way, to Rosencrantz and Guildenstern, tricksy betrayers of Hamlet’s trust, Shakespeare’s characters often find friendship a difficult bond to manage.

Particularly ticklish is the possibility of conflict between friendship and marriage. In The Merchant of Venice, Bassanio promises his stricken friend Antonio that although he is ‘married to a wife / Which is as dear to me as life itself’, she is ‘not with me esteemed above thy life.’ Bassanio vows to ‘lose all, ay, sacrifice them all’ to release Antonio. Noble sentiments, but not uttered without challenge. Bassanio’s new bride Portia is present, in disguise as a lawyer, to hear his pledge: ‘Your wife would give you little thanks for that / If she were by to hear you make the offer,’ she mutters, sotto voce.

For some people in early modern England, it wasn’t matrimony that was the highest form of human relationship, but friendship – and in particular, friendship between men. George Wither, the author of a celebrated collection of emblems, captured this sense of exemplarity in his image of friendship. The illustration – two male hands clasped above a single flaming heart, surrounded by a pair of conjoined rings – is accompanied by a short verse: ‘That’s friendship, and true love indeed, / That firm abides in time of need’.

Michel de Montaigne, the French essayist, argued that intense friendship was a profoundly passionate connection that drew its actors into an irresistible bond. Friends ‘intermix and confound themselves one in the other, with so universal a commixture that they wear out and can no more find the seam that hath conjoined them together.’ Writing of his own fervent relationship with the political philosopher Étienne de la Boétie, he admitted that he didn’t fully understand the force that ‘having seized all my will, induced the same to plunge and lose itself in his; which likewise having seized all his will, brought it to lose and plunge itself in mine.’

In many ways, ardent language like this is untypical of the time. Renaissance men and women – especially educated men and women – were expected to keep their passions under control. They were advised not to give in to their bodily urges, or gluttony, or rage. But pure friendship, amicitia perfecta, was different. In its truest state, it could only be experienced at a very high temperature.

In part, this was because the idea of amicitia perfecta was drawn from classical example. Anyone in the sixteenth century who went to school or learnt Latin from a tutor would have read and translated Cicero’s De amicitia (On Friendship), a treatise that celebrated friendship between virtuous men. Drawing on sources that included Aristotle’s Nichomachean Ethics, Cicero laid out a philosophy of friendship that could be condensed to a few catchy proverbs: the friend was ‘another self’, and friends shared ‘one soul in two bodies.’ Even as impressionable Elizabethan pupils learnt Latin grammar, they absorbed Cicero’s praise of friendship, and learnt to esteem the examples of ideal friends from classical and Biblical history: Damon and Pithias, Orestes and Pylades, Achilles and Patroclus, David and Jonathan.

All of these exemplars of perfect friends were men, and men of rank. And this is another reason why it was held to be an acceptable thing to experience friendship with passionate intensity. Friendship was defined in treatises as something that could only exist in its perfect form between men of intellect, moral courage and ethical firmness – only the male frame was believed to be capable of withstanding the rigours of powerful emotions.

Such a misogynistic view was established medical opinion in the sixteenth and seventeenth centuries. Orsino, the love-sick duke in Twelfth Night, evidently believes it. Speaking to his page Cesario (who is, of course, Viola en travesti), he explains that his powerful devotion to the impassive Olivia is by definition a somewhat one-sided affair: ‘There is no woman’s sides / Can bide the beating of so strong a passion,’ he claims. Viola, nobly suffering her own unutterable love for Orsino, silently disproves him.

Renaissance dramatists were interested in stories which challenged established views about friendship. The Shakespearean stage was the ideal space to dispute the gender and class constraints that traditional philosophy placed on the definition of friendship. In The Two Noble Kinsmen, the apparently perfect friendship between Palamon and Arcite crumbles at the first sign of female competition, but Emilia’s intense and erotic friendship with Flavinia lives on untarnished in her memory: we are in no doubt that ‘the true love ’tween maid and maid may be / More than in sex dividual.’