The online Merriam Webster defines myth as “a usually traditional story of ostensibly historical events that serves to unfold part of the world view of a people or explain a practice, belief, or natural phenomenon.” By contrast, folklore is defined as “traditional customs, tales, sayings, dances, or art forms preserved among a people.”
In the frontmatter to Ireland’s Immortals: A History of the Gods of Irish Myth Mark Williams points to two definitions that in his opinion encompass Irish mythology: Wendy Doniger’s “a story that a group of people believe in for a long time, despite massive evidence that it is not true” and Heather O’Donoghue’s “stories about the gods.”
The latter is especially interesting to Willams. He writes that many Europeans who became Christian tended to demonize their ancestors’ gods, whereas the Irish took a different approach: they believed that the loose pantheon of Celtic gods once known as the Tuatha De Danann, were historical people whose deeds were memorialized in a legendary history. Authors would describe the gods as half-fallen angels, or as a branch of sinless humans. Regardless, because none of the pre-Christian Celts wrote down their stories, every primary source about the Celts and their religion is written by either a non-Celt or Christianized descendants of the Celts. This does not mean that there is nothing to gain from the stories. It just means that when reading the sources of the myths, one must be diligent about not taking everything at face value.
A great resource for undergraduates to start engaging with Celtic myth primary sources is The Celtic Heroic Age: Literary Sources for Ancient Celtic Europe and Early Ireland and Wales, ed. by John Koch in collaboration with John Carey, a collection of translations into English. This is a perfect book for those seeking only translations, but it provides little context, for example about the importance of the works. Peter Berresford Ellis’s The Chronicles of the Celts: New Tellings of Their Myths and Legends fills that gap. It is a wonderful collection of Celtic myths and legends from the countries with surviving Celtic languages: Ireland, Scotland, Wales, Isle of Man, Cornwall, and Brittany. Ellis offers great summaries of the myths alongside a generali history of the Celts and their legends. He also provides artistic interpretation for some of the stories. Another great primary resource is Early Irish Myths and Sagas, translated, introduced, and annotated by Jeffrey Gantz. Gantz offers a solid general introduction to the history of the Celts, Irish storytelling, and manuscripts, and he also introduces each myth. Philip Freeman provides a similar treatment in Celtic Mythology: Tales of Gods, Goddesses, and Heroes and he covers Welsh mythology as well. Another example of artistic interpretation is the work of Lady Gregory, which includes Gods and Fighting Men and Cuchulain of Muirthemme.
As specified earlier in this essay folklore involves “traditional customs, tales, sayings, dances, or art forms preserved among a people.” This body of work centers on the collectors. Collecting Celtic folklore began with Thomas Crofton Croker, who, as Richard M. Dorson points out in his invaluable The British Folklorists: A History,1 was the first English-speaking person in the world to collect and publish folktales. When he was first starting out, Croker gathered folklore by writing it down as travel accounts or taking it from antiquarian descriptions. Ultimately, he framed the folktales in two ways: journalistic observations that evolved into a story or essay, or recordings of the storyteller, with a transcriber writing down sounds as letters. These methods would be employed throughout the 19th century. Croker’s first great work, comprising two titles, focused on songs and stories of the country people; Popular Songs of Ireland and Fairy Legends and Traditions of the South of Ireland. The latter book leads to the important folklorist Thomas Keightley. When collecting folktales for the Fairy Legends and Traditions, Croker had assistance from various contemporaries, none of whom received credit or compensation for their time and efforts. Keightley was one of those individuals and he claimed to have provided not only tales but also most of the comparative notes (as reported in Folk-Tales of the British Isles, chosen and introduced by Kevin Crossley-Holland). That this happened is regrettable but it sparked an interest in Keightley that inspired him to write The Fairy Mythology: Illustrative of the Romance and Superstition of Various Countries. In addition to an assortment of Celtic fairy tales, Keightley includes fairy tales from all over Europe, with some sections dedicated to the different kinds of fairies. This is a great resource for anyone interested in exploring European folklore in general.
Also valuable is William Carleton’s Tales and Stories of the Irish Peasantry. Carleton had three approaches to collecting folktales. First, he used the tale as a colorful element, where the style of the author was different from the style of the characters, as if the author was an observer. The second was an approach in which the author retold a tale to fit a different and new audience. The third was that of a historian: the tale was (as described in Irish Folktales, edited by Henry Glassie) “told as fact, worthy of preservation for the information it contains about the people who are not the author.”
1. The author of this essay notes in particular, and is grateful for, the late Richard Dorson’s The British Folklorists, which provided a wealth of information for this essay.
Fairy Legends and Traditions of the South of Ireland by 
Folktales of the British Isles by 
