I won't lie - I'm no fan of Robert Graves and I doubt you'll find many Reconstructionists who are. Writing in the 1940's Graves still had the Victorian mentality that said it was perfectly fine to invent history if the story you were spinning seemed logical to you. And in fairness Graves was no scholar but rather a poet and his work is the work of a poet. There is an excellent book by Mark Carter called 'Stalking the Goddess' which dissects Graves book the White Goddess and sheds a lot of light on how it came to be what it is, and I highly recommend anyone interested read both Graves' book and Carter's.
Before we get into what exactly Graves created, why the false history is problematic, and how these ideas are now shaping paganism, I want to be clear about one thing. Many of the concepts Graves put forth do have great value today and believing them or following them isn't necessarily a bad thing. In fact some of them have led to very deep and meaningful theology and that should certainly be kept. Where the problem comes in is with the idea that these things are far older than they actually are and with a pervasive attempt to retrofit the original pagan culture to fit modern concepts that are foreign to them. When Graves wrote he called his product Celtic and attributed his ideas to the pagans of the various Celtic cultures in ways that were at best misleading and at worst intentionally duplicitous and that has left a seemingly indelible mark on neopaganism.
The White Goddess was published in 1948 and is arguably one of the single most influential books to shape modern paganism as we know it today. It is from Graves that we get many concepts that are foundational to mainstream paganism including the triple goddess, oak and holly kings, 'Celtic' tree calendar, and the Druidic gods Druantia and Hu Gadarn. To be clear all of these concepts as they are now understood in paganism don't date back before Graves' book and are not historically Celtic*. Nonetheless because of Graves work the majority of people believe in the historicity of these things and they have been perpetuated as genuine in countless subsequent books and other resources.
The idea of the triple Goddess as outlined by Graves was based on the relationship between the poet and the 'muse' which was his Goddess. He describes her in various ways throughout the text, from a bride, mother, and 'layer out' (i.e. death goddess) to a girl, woman, and hag, although clearly it was as maiden, mother, and crone that we came to know her best. He related this triplicity to spring, summer, and fall as well as to the new, full, and waning moon. His views and description of this muse/Goddess are entirely in relation to the male poet and are, in my opinion, heavily misogynistic in tone: his main triad is the Mother/Bride/Layer Out based on the idea that it is the mother who births and nurtures the poet, the bride who marries him and is his lover, and the layer out who kills him, thus encompassing his entire life. In other words his muse/Goddess is structured on how the male poet is cared for/served by this female energy throughout his life. This concept however was taken and expanded - and obviously heavily edited and re-shaped - by modern paganism to form the more familiar Maiden/Mother/Crone triple Goddess most of us are familiar with. There have also been numerous attempts to create a male triple counterpart to the female one invented by Graves, to balance it for those who like the system.
From a historic perspective there is no, to my knowledge, Celtic triple Goddess as Graves envisioned her. Generally when we see Goddesses in groups of three, such as the Morrigan or Brighid, they are age-equals, usually sisters. When we look at examples like the Gaulish Matronae we sometimes see one younger woman with two older ones, but never the range of young, middle aged, and old. In fact as far as I know it is unusual to see Celtic goddesses depicted exclusively as elderly - although of course many of them can sometimes appear so, they are understood to be ultimately ageless. This becomes a problem when people who do like the idea of the Triple Goddess try to fit pagan Goddesses into the mold which, in my experience, rarely seems to work well. In contrast though I have seen some amazingly intense results from people connecting directly to the, for lack of a better term, archetypes of the Maiden, Mother, and Crone.
The Oak and Holly Kings are similarly an idea that was first suggested in that form by Graves. Drawing on Frazer's idea from 'The Golden Bough' of a divine King and looking at a variety of paired deities in mythology including Lugh and Balor and Llew and Gronw Pebr, as well as myths of the Robin and Wren, Graves suggested a seasonally reoccurring battle for dominion of the year that would happen at the solstices. At the summer solstice the Holly King would win and usher in the dark half of the year, while at the winter solstice the oak king would win and bring back the light half. This idea of course has been widely adopted by many Wiccan and neopagan groups and has become a familiar theme to the Wheel of the Year.
The problem, such as it is, with the Oak and Holly kings isn't that they don't work well as a modern concept but only that they didn't exist as one historically. While they may be loosely based on similar mythic themes the Kings themselves are decidedly an invention of Robert Graves. Its telling that Graves chose the solstices, two holidays that we have no existing significant information about in Irish mythology, and not the far more important Bealtaine and Samhain as his turning points of the year. We do know from surviving myth and folklore that it was at Bealtaine and Samhain that the year turned from dark to light and back again, so it is highly suspicious to think that there would have been an old belief about Kings fighting and turning the year six weeks later at the solstices. The theme itself is clearly sound and rooted in older motifs, and I don't think anyone disputes that, but the particular iteration of Oak and Holly Kings and the fight on the solstices to eternally turn the year are unique to Graves.
The tree calendar may be my biggest personal pet peeve to come from the White Goddess because it is constantly and ubiquitously spread around as ancient and druidic when it is neither. I highly recommend Peter Berresford Ellis's article 'The Fabrication of Celtic Astrology' and Michel-Gerald Boutet's 'Celtic Astrology; A Modern Hoax' for in-depth debunking of the tree calendar and related Celtic astrology, but the short version is that Graves made it up. We have no surviving information on the exact calendar used by the pagan Irish, but we can be certain it wasn't based on the Ogham because we do have a great deal of surviving Ogham material, none of which references calendar use. Also looking at the 13 month calendar created by Graves we can see several red flags. He begins his calendar not in November around Samhain (the beginning of the new year and shift to winter) or aligned with the moon phases, but rather on December 23 to line up with the winter solstice and the birth of a sun god - except the Irish have no deity born on that date as far as I know, and most explicitly solar deities in Ireland are female (the word for sun is female as well). Also in order to make the calendar work Graves had to cut the letters down from 20 to 13, which he did by ignoring the work of some of the premiere Ogham scholars of the day, including his own grandfather Charles Graves who was president of the Royal Irish Academy, and relying instead on the work of a highly controversial and criticized fringe scholar of the time (Ellis, 1997). He also focuses exclusively on the Tree Ogham, despite the fact that this was only one of many types of Ogham in use, and was no more or less significant or likely to be used for any purpose than any other Ogham. Basically he took what suited him of the available information and just ignored everything else to form what he wanted. It is certainly a workable modern system and many people today like it, but it did not exist before Graves created it.
Now on to the Druidic Gods Graves claimed - Druantia and Hu Gadarn. To start with Druantia, the Goddess that Graves suggested Druids worshiped: simply put she never existed at all historically. The name seems to be based on the same root as the word Druid, one might assume meaning oak. However there is no evidence of this Goddess anywhere prior to Graves book. Hu Gadarn, his universal Druidic God is a real mythic figure at least, but not a God of the Druids, rather Hu comes to us via Iolo Morgannwg's (aka Edward Williams') highly controversial and forged Myvyrian Archaiology, although Iolo didn't make him up either (Jones, 2009). Hu has a really complex history, coming from a French tale to Wales, possibly as an older reflex of an original Celtic story, but ultimately we can say very little with certainty about Hu except that he seemed to be associated with plowing (Jones, 2009). He certainly wasn't the Welsh horned God or Druidic deity that Graves imagination painted him to be. Both of these figures have found a solid place in modern neopaganism appearing now in books and websites on Celtic paganism and referenced as if they were in fact truly ancient. I will never criticize people who feel a genuine connection to any deity and if you honor either of these beings and find them present and receptive, good. I can only lay out the actual history of each of them as we have it.
The White Goddess has clearly had a profound impact on modern pagan theology, although in ways that people are often not aware of. It is not the new theology itself that is the ultimate problem with Graves' work, but the way it has found a place in modern paganism under the guise of ancient beliefs that make some people dislike it. I am not the only person, by far, who takes issue with Graves work and its muddying effect in modern paganism by the way. Ronald Hutton in his book 'The Pagan Religions of the Ancient British Isles' referred to the White Goddess as "a major source of confusion about the ancient Celts and influences many un-scholarly views of Celtic paganism" and Hilda Ellis Davidson in her 'Roles of the Northern Goddess' said about Graves that he "misled many innocent readers with his eloquent but deceptive statements about a nebulous goddess in early Celtic literature". In other words, it's books like this that portray poetic inspiration and the author's opinions as ancient pagan belief that actively harm modern paganism by giving us a false basis to build from. Rather its better to be clear on what is inspiration and what is modern belief and embrace it for the value it has rather than cling to an idea of a history that never existed and is easily disproven.
I encourage people who have adopted Graves ideas to read the White Goddess for themselves and see how the author originally presented the concepts, as it is quite fascinating to see the seeds that have grown into such deep rooted theology in the last 68 years. It really is quite amazing to think of the way that, within three generations, more or less, the pagan community has seized on these ideas and incorporated them so thoroughly and in such important and vital ways. Its hard to imagine modern paganism without the imagery of the triple Goddess or the seasonal Kings turning the wheel of the year, and I say that as someone who doesn't even adhere to those traditions. But please, lets stop calling the tree calendar 'ancient' and 'Druidic', and lets not try to frame the modern triple goddess and Oak and Holly Kings as the powers worshiped by the pagan Irish a thousand years ago. Call a spade a spade and understand these things for the modern concepts they are, which in no way lessens their practical value but certainly changes how we might understand the past cultures.
*I'm choosing to focus here specifically on aspects of the White Goddess which have impacted modern pagan theology; an entire other blog could arguably be written just about the book's misrepresentation of Celtic mythology itself. For one example see Brian Walsh's blog entry 'Desecrating Graves (Introduction to the Song of Amergin Part II)' which discusses the serious problems with Graves' treatment of the Song of Amergin in his book.
Ellis, P., (1997). The Fabrication of Celtic Astrology http://cura.free.fr/xv/13ellis2.html
Jones, M., (2009). Hu Gadarn
Graves, R., (1948). The White Goddess