The question of the nature of linguistic evidence, and of what textual sources actually attest, is a slippery one for synchronic linguists investigating their own native language, so it is unsurprising that it should also be a hard one for the diachronic analyst. The widespread use of the term diglossia may have done little more than create confusion in the linguistic analysis of individuals in complex monolingual speech communities and the textual evidence. The consequence is that phonetic change can progress a long way without evidence for it being directly attested in a written source. The realization of this dissociation was the main motivation for the twentieth-century reconstruction of proto-Romance on the basis of extrapolating backwards from medieval Romance written evidence rather than by examining the written texts provided for readers by those who supposedly spoke it.