Abstract We begin with sound-form symbolism (the “Bouba-Kiki effect”) and point out its relevance to a wide range of psychological phenomena such as (1) the origin of words, (2) cross-sensory metaphors (e.g., the “loud”-ness of a shirt and the “sharp”-ness of cheese), conceptual metaphors (“Juliet is the sun”), and (3) sensory-motor congruence exemplified by the mirror neuron system. We suggest that these diverse aspects of the mind involve cross-domain interactions. Such interactions, and the dissolution of rigid barriers between brain modules, appeared as an evolutionary novelty giving the human brain its unique, “abstract attitude”—resulting partly from the accelerated expansion of the dominant inferior parietal lobule and Wernicke's area. Cross activation from late to early stages of visual processing may also enable more vivid imagery in humans—an ability that is amplified in grapheme color and “calendar line” synesthetes.