How do you invent a word? First, you have to detect a gap in the lexicon, a semantic lacuna that can be readily filled. Then you must steep yourself in the languages that English has borrowed from, which is pretty much all of them. Or at least get your head around a heap of etymologies, word roots, prefixes and suffixes, so that your word can pass for native. Now comes the trickiest part: you have to get people to adopt it.

Late one night, about five or six years ago, John Koenig conjured up the word ‘sonder’ and its meaning – the awareness that everyone around.