John Joseph writes in the TLS that Saussure’s insight that language is “purely differential and negative in nature” was a commonplace of late nineteenth-century philosophy and “was a defining feature of British psychology.” And Saussure’s claim that meaning is arbitrary and conventional also has a long pedigree. Saussure’s “novel contribution was to imagine the sound side of language on the one hand, and the conceptual side on the other, as perfectly alike in their nature and mental operations. This is the ‘double essence’: two orders of difference, held together by a force that is essentially social, which he called the immutability of linguistic signs. It makes it impossible for an individual to introduce a change into the sign system, and it means that any communal change creates a wholly new system of values, which is to say a new language.”

Joseph also reveals that Saussure was a synaesthete, for whom (for instance) the French sound “a” felt “off-white, approaching yellow; in its consistency, it is something solid, but thin, that cracks easily if struck, for example a sheet of paper (yellowed with age) drawn tight in a frame, a flimsy door (in unvarnished wood left white) that you feel would shatter at the slightest blow, an already broken eggehsll that you can keep cracking by pressing on it with your fingers. Better still: the shell of a raw egg is a (whether in colour or consistency of the object), but the shall of a hard-boiled egg is not a , because of the feeling you have that the object is compact and resistant” (all this from Saussure).