A key text of twentieth-century thought went missing decades ago. More mysterious than the loss itself has been our indifference to it: the affair was never widely publicized, and even those in the know have tended to regard the disappearance as a bibliographic curiosity rather than as reason for serious regret. I am referring to Jacques Lacan, “The Mirror Stage”. To be clear, I do not mean Jacques Lacan, “The Mirror Stage as Formative of the I Function as Revealed in Psychoanalytic Experience”, delivered on 17 July 1949 to the Sixteenth International Psycho-Analytical Congress in Zurich and published the same year in the Revue Française de Psychanalyse. I mean instead the earlier version with the shorter title, sometimes said to have been published in 1937, among the acts of the Fourteenth Annual Psycho-Analytical Congress in Marienbad, in The International Journal of Psycho-Analysis, vol. 18. What one actually finds here, on page 78, sandwiched between summaries of papers on “The Dynamics of Puberty” and “The Early Diagnosis of Psychoses in Analysands”, is only this brief notice: “2. Dr. J. Lacan (Paris). The Looking-Glass Phase”. And that is all.

This part of the mystery, at least, is easily solved: Lacan himself, en passant in later writings, admits to being the immediate culprit, though he assigns ultimate blame to Ernest Jones, President of the Congress, “a position for which he was no doubt qualified by the fact that I have never encountered a single English colleague of his who didn't have something unpleasant to say about his character”.

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.