"[L]et's not lose track of the purpose of all this imagery, which is to suggest helpful ways of imagining what a human soul's essence is. If we map each tree (or nucleus) in the crystal lattice onto a particular human brain, then in the tight-binding model (which corresponds to the caged-bird metaphor), each brain would possess a unique soul, represented by the cloud of timid butterflies that hover around it and it alone. By contrast, if we think of a metal, then the cloud is spread out across the whole lattice — which is to say, shared equally among all the trees (or nuclei). No tree is privileged. In this image, then (which is close to Daniel Kolak's view in I Am You), each human soul floats among all human brains, and its identity is determined not by its location but by the undulating global pattern it forms."