William Blake’s oeuvre contains a range of works, which though each is unique, participate for the most part in a common mythology. Jerusalem: The Emanation of the Giant Albion is one such work, a long (100-plate) illustrated poem; actually his magnum opus. Jerusalem explores the process by which humanity (represented by Albion) is restored to a divine culture based in loving relationships, whose arts and sciences are inspired by creative genius.
At one point in the story, the hero-protagonist, Los, who is a blacksmith and artistic genius, becomes roofed in and thereby trapped within the world of the materialistic world-view. He is now isolated from the Vision of Eternity, no longer able to access this vision as a living experience in communion with the universe, and beyond.
This vision, for Blake and the Romantics in general, is the imagination, which is not the same as fantasy, or fancy, as we might consider such today. Fancy (as it is differentiated by the Romantics, is a private form of imagination, which is not imagination proper. Rather, imagination itself (sometimes written capitalised, Imagination) is defined by the Romantics as fundamental to the universe itself; it is the primal creative power of existence (whether arising from Nature or the Divine), which humans may also participate in. This participation is often described as accessible through the power of individual genius. The artist, through their genius, may share in the creative process inherent in the universe itself.
Fancy differs – though is often mistaken for imagination – in that remains within individual images of the personal unconscious, the creations wrought around the individual ego-persona, with all its misconceptions, limitations, and biases. Imagination in contrast is considered universal, broader even than the collective human unconscious . This is the basic difference between imagination and fancy.
So, at the point in Jerusalem (around plate 19) where Los is trapped within the material world, humanity (represented by Albion) withdraws within itself, into the inner, lunar worlds of personal fancy. There Albion meets with Jerusalem, who is his eternal feminine counterpart, though she also trapped within the rock-like material-consciousness, due to the oppression of materialism. The individual imagination has been reduced to personal fantasy.
But Blake’s mythos ends on a high note; it is romantic-comedy, not tragedy. Eventually, when Albion and Jerusalem are both liberated from the reductionist world-view, they merge into the infinite creative imagination as the divine integrated human, and take their place once again in eternity. Albion becomes the creative will, and Jerusalem, the capacity for loving relationship.