Synaesthesia is best known as the name of the condition of those individuals who regularly experience one kind of sensory stimulus simultaneously as another – and who almost universally regard their atypical kind of perception as a gift rather than an affliction. The commonest variety of synaesthesia associates particular sounds with particular colours, a phenomenon that is itself best known by the French term audition colorée. Roughly contemporary, however, with modern interest in this clinical phenomenon has been the broader application of synaesthesia to the sensory blending experienced by all readers, synaesthetes or not. This happens through literature's “use of metaphors in which terms relating to one kind of sense-impression are used to describe sense-impressions of other kinds”, as the Oxford English Dictionary puts it, providing an example of this usage from W. B. Stanford's Greek Metaphor (1936), which introduced the term to many classicists in a discussion “On Synaesthesia or Intersensal Metaphor”.

Interest in both kinds of synaesthesia has its roots in the seventeenth and eighteenth centuries, which saw an explosion of philosophical and scientific enquiry into the nature of sensation, cognition and aesthetic pleasure. The very term aesthetic in its modern meaning first appeared in this period, applied by the philosopher Alexander Baumgarten to our sensual experience of a work of art, something which, he argued, both preceded and transcended our mental or “noetic” appreciation of the same. Etymologically, synaesthesia and aesthetic(s) alike can be traced back much farther, to the Greek verb for experience, aisthanomai, and its cognates and compounds.