So the manuscript breaks off as we hear that Manawydan has never met a more beautiful woman than Rhiannon. In the First Branch of Y Mabinogi she arrives with a magical aura about her but soon makes her presence felt as a real enough woman letting Pwyll know what she wants from him. In the Third Branch, the beginning of which the above illustrates, she is even more practically present as Manawydan’s wife at least until she passes into an enchanted fort. She has, as any ordinary woman, grown older from the First to the Third Branch, re-married and plays her part in the domestic events of the tale. But between these, in the Second Branch, her birds sing over the sea to those that returned from Ireland, “and all the songs they had ever heard were harsh by comparison”. In Culhwch and Olwen these same birds of Rhiannon are said to “wake the dead and lull the living to sleep”. We might wonder how two tales that lead one into the other, regard the same character at once as a person in the story and an other-world enchantress with magical birds?
One answer is to say that elements came into the tale from different stages of an earlier mythological tradition, but this suggests a tale-teller that wasn’t in full control of the material. Whatever we think of Culhwch which is full of what might be regarded as loosely integrated folk-tale material, the author of the Four Branches does seem to be writing stories in which the elements are consistently integrated. But the two identities of Rhiannon do not seem consistent even in the context of interactions between Thisworld and the Otherworld. The final pages of Branwen eerily evoke an otherwordly atmosphere in contrast to the matter-of-fact way characters move between the two worlds in the other tales.
How can the ghostly and scarcely human Rhiannon of the birds suddenly become Manawydan’s wife? Could the author engage in a sort of double-think? We could propose that the sensibility of medieval authors was different from ours so that they could know what they were dealing with in terms of earlier mythical material while at the same time get on and present a story set in the world they inhabited. Sometimes with medieval literature it seems so, but at others medieval writers appear prone to an intense literalism attached to material objects like obviously fake holy relics. It might be that they knew full well that they were fakes but nevertheless were able to believe in their efficacy. The art of thinking mythically and literally at the same time is one that is more difficult for modern readers. One way to open the borders between the worlds is to cultivate that art, which does not imply either a naive credibility or a cunning sophistry, but a creative openness to the life of the soul-world as well as the life of the physical-world, bringing together what should never be parted.
awenydd.cymru 
Yes, I’d agree that one of our biggest challenges as modern readers and writers is to bring together authentic represenations of physical reality with those of the myth world. The ‘reward’ of the challenge being that when they do meet and we perceive that we meet there is that feeling of enchantment and wonder found Rhiannon’s stories.
I think she can live in both worlds and be differently at home in either.
I think we can too if we have the gift.