Odin’s quest for wisdom is never-ending, and he is willing to pay any price, it seems, for the understanding of life’s mysteries that he craves more than anything else. On one occasion, he hanged himself, wounded himself with his spear, and fasted from food and drink for nine days and nights in order to discover the runes.
On another occasion, he ventured to Mimir’s Well – which is surely none other than the Well of Urd – amongst the roots of the world-tree Yggdrasil. There dwelt Mimir, a shadowy being whose knowledge of all things was practically unparalleled among the inhabitants of the cosmos. He achieved this status largely by taking his water from the well, whose waters impart this cosmic knowledge.
When Odin arrived, he asked Mimir for a drink from the water. The well’s guardian, knowing the value of such a draught, refused unless the seeker offered an eye in return. Odin – whether straightaway or after anguished deliberation, we can only wonder – gouged out one of his eyes and dropped it into the well. Having made the necessary sacrifice, Mimir dipped his horn into the well and offered the now-one-eyed god a drink.
The most general and obvious message of this tale is that, for those who share Odin’s values, no sacrifice is too great for wisdom. The (unfortunately fragmentary) sources for our current knowledge of the pre-Christian mythology and religion of the Norse and other Germanic peoples are, however, silent on exactly what kind of wisdom Odin obtained in exchange for his eye. But we can hazard a guess.
The fact that Odin specifically sacrificed an eye is surely significant. In all ages, the eye has been “seen” as a poetic symbol for perception in general – consider the astonishing number of expressions, both in everyday usage and in the works of the great canonical poets, that use vision as a metaphor for perceiving and understanding something. Given that Odin’s eye was sacrificed in order to obtain an enhanced perception, it seems highly likely that his pledge of an eye symbolizes trading one mode of perception for another.
What mode of perception was exchanged for what other mode, then? The answer to this question lies in the character of Mimir. Mimir, whose name means “The Rememberer,” seems to have been the being who told the gods how to live in accordance with ancestral tradition, and with wisdom more generally.
In the tale of Odin’s discovery of the runes, Odin sacrificed what we might call his “lower self” to his “higher self.” Here, his relinquishment of an eye should surely be understood along similar lines: he exchanged a profane, everyday mode of perception, beleaguered with countless petty troubles, for a sacred mode of perception informed by divine, ancestral wisdom.
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 Bauschatz, Paul C. 1982. The Well and the Tree: World and Time in Early Germanic Culture.
 The Poetic Edda. Völuspá, stanza 28.
 Snorri Sturluson. The Prose Edda. Gylfaginning 15.