“There are these welcome, albeit fancy acknowledgments of the three problematic elements of metaphoric imagining: discernment of similarity in disparate, imaginal double sight, and disclosure of what might be called truthful unreality. Can there be metaphor entirely without the middle factor, the imaginal element?

It seems to me impossible. For example “The brain is a computer” is a metaphor in which the soft brain and the hard computer are images disparate enough to keep tenor and vehicle from collapsing (while the »tertium comparationis is vague enough to rank this rope among the walking dead). On the other hand, its careful non-imaginal counterpart, “The human reason is a Universal Turing Machine,” is no metaphor but a straight identity (a proposition that is very much alive). In other words, as the sensory shape drops away, the metaphor, or rather its simile-expansion, first yields an intellectual analogy, and the analogy in turn yields, upon further abstraction, an identity of relations. Unenvisionable metaphors often turn out to be statements proposing unexpected identifications.”

— Eva Brann, The World of the Imagination, Sum and Substance