In 1923 Kandinsky proposed a universal correspondence between the three elementary shapes and the three primary colors: the dynamic triangle is inherently yellow, the static square is intrinsically red, and the serene circle is naturally blue.
The series ▲■● represents Kandinsky’s attempt to prove a universal correlation between color and geometry; it has become one of the most famous icons of the Bauhaus. Kandinsky conceived of these colors and shapes as a series of oppositions: yellow and blue represent the extremes of hot/cold, light/dark, and active/passive, while red is the intermediary between them. The triangle, square, and circle are graphic equivalents of the same polarities.
In March 2021, I went through a fun self-imposed experiment: no emoji for 2 weeks. Not on social media, not in private messages, not even as Slack or Discord reactions. No emoticon either: the goal was to communicate without illustrations, only with words. I did a semi-rigorous (a.k.a. half-assed) diary study, taking notes on my feelings and behaviour.
I'd like to call the more general phenomenon that this is a specific instance of "ghost knowledge": It is knowledge that is present somewhere in the epistemic community, and is perhaps readily accessible to some central member of that community, but it is not really written down anywhere and it's not clear how to access it. Roughly what makes something ghost knowledge is two things:
It is readily discoverable if you have trusted access to expert members of the community.
It is almost completely inaccessible if you are not.
In this sense, most knowledge is ghost, particularly if you take an expansive view of what counts as an epistemic community.