A burn from the cooking salmon gave Fionn access to the wisdom held by the fish. The knowledge included prophetic understanding, and thereafter he could discover answers by sucking his thumb.
Fionn and the Salmon of Knowledge
The salmon came to Finnéces’s line after the old druid had waited seven years for it. He caught the fish and set it to cook beside the water. The boy Fionn, then called Demne Máel, watched it turn on the spit. Finnéces warned him not to touch or taste the salmon, because it held great wisdom.
Hazel bushes grew beside the pool. Their nuts fell into the water, and the nuts contained the wisdom of the world. The salmon ate them and gained their knowledge. As the fish cooked, it sizzled and spat. Grease or liquid struck Fionn’s thumb and burned him. Without thinking, he put the injured thumb into his mouth.
Wisdom passed into Fionn at once. He gained the knowledge that Finnéces had hoped to obtain, including prophetic understanding. After this, Fionn could find the answer to almost any question by chewing his thumb. The Fenian narratives give variant names for the fish. It is sometimes called Fintan, a bard who had lived through many incarnations. It is also called Goll Essa Ruaid, the one-eyed salmon of Assaroe. The account therefore links Fionn’s wisdom to the salmon, the hazel nuts, and the brief act that transferred the knowledge to him.
Fionn Becomes Leader of the Fianna
Goll mac Morna returned from exile, defeated Cumhal, killed him, and scattered the Clan Baíscne. Cumhal’s posthumous son was taken away and raised in secret. He trained in martial skills and became a capable warrior. After defeating a rival in a contest, he was called Fionn, meaning “the fair boy”. He was also known as Fionn mac Cumhaill, Fionn son of Cumhall.
Fionn continued his training with the warrior woman Buanann and the warrior Cethern mac Fintain. By manhood, he could run faster than any other person, strike his target with a spear, and swim across any body of water. He could also suck his thumb and learn the whereabouts and weaknesses of an enemy. His skill and judgement won him recognition as a warrior.
For a time, the Fianna served the High King of Ireland. They remained ready to march against disturbances within Ireland or foreign enemies. Their demands angered the people, while their pride offended the king. Disputes within the Fianna led to fighting among themselves. The king and the people then joined forces against them.
Before this decline, Fionn performed a deed of prowess and the High King offered him a boon. Fionn asked for his lawful inheritance and declared his name. The king ordered Goll to acknowledge Fionn’s rights. Goll opposed him and claimed the chieftainship of the Fianna. Fionn accused Goll of murdering his father and ruling wrongfully. He challenged Goll to mortal combat. The king gave the signal. Fionn proved his martial ability, and the High King recognised his claim. Fionn became leader of the Fianna despite Goll’s opposition.
Fionn and the Enchanted Doe
Sadhbh wore the shape of a doe when Fionn encountered her. He fell in love with her despite the form imposed on her. They came together, and Sadhbh later gave birth to a son. They named the child Oisín, meaning “little fawn”.
Oisín remained human, but he carried a mark of his mother’s enchantment. One account says that Sadhbh had been warned that licking her human baby would turn him into a deer. She avoided doing so, although her tongue touched his forehead slightly. The boy therefore kept a small tuft of deer fur there. Another account places the fur across his eyebrows.
Oisín grew into a gifted poet and a capable warrior. He travelled with Fionn and the Fianna, the band of warriors who followed Fionn and guarded Ireland against invaders. The Fenian narratives present Fionn as fearless and wise. They present Oisín as the most eloquent of his peers.
Sadhbh did not remain with Fionn. The otherworldly Dark Druid reclaimed her and took her back to the world beyond ordinary human life. Oisín stayed with Fionn and the Fianna. His name and the small mark on his head recalled his mother’s doe shape.
