ELEMENTS of the erotic appear in much medieval Welsh literature, such as the romantic heroic exploits depicted in the three Welsh Arthurian Romances and more playfully shocking themes, as evidenced by Dafydd ap Gwilym's complaint to his penis and Gwerfel Mechain's response in praise of her genitals. The Fourth Branch of the Mabinogi is no exception to this penchant for the passionate, replete with its references to sexual encounters that both spark the erotic imagination and serve an instructive social purpose. Recounting erotic situations in and of themselves is not the redactor's primary objective: he uses the erotic potential of his tale to convey the message that misapplied passion and lust result in the breakdown of society. Suggestive rather than descriptive, the erotically charged passages in the Fourth Branch illustrate some sort of failure of social order, and this is no surprise: transgressive love is a staple of medieval literature.

The Fourth Branch, with its symbolic interpretations of everyday social obligations, communicates the necessity of maintaining social bonds and suggests that trespass of social and familial obligations requires redress and reparation. Myth communicates a number of sentiments – rules for social interaction, ethical conduct and even religious beliefs – and enforces a moral order necessary for group survival. As Roberta Valente notes in her Merched y Mabinogi, the Four Branches contain guidelines of behaviour that depend on both an individual's obedience to such codes and that individual's ability to interpret difficult situations where principles conflict or are non-existent.