From the early 19th century, comparative linguists, notably Lorenz Diefenbach, identified the Cauci with the Germanic Chauci of the Low Countries and north-western Germany, a parallel already drawn by earlier antiquarian scholarship.^[2] Proponents of this view also pointed to the fact that the Manapii (Μανάπιοι), who in Ptolemy's map border the Cauci to the south, likewise bear a name that is almost identical to that of another continental tribe, the Belgic Menapii in north-eastern Gaul.

This correspondence appeared to testify to population movements between the two regions. The linguistic aspect of this hypothesis was most recently (1917) developed by Julius Pokorny,^[3] although the Cauci-Chauci association is not universally accepted.^[4] This early scholarship also drew attention to apparent parallels among Celtic or Celticized peoples of the Iberian peninsula, specifically a leader of the Lusitani named Kaukainos (Καυκαῖνος), and a city called Kauka (Καύκα) (modern Coca), inhabited by Kaukaioi (Καυκαῖοι), among the Vaccaei, a prominent Celtic tribe of the Iberian Peninsula that spoke a Hispano-Celtic language.^[5]

With regard to possible descendants of the Irish Cauci, Pokorny and Ó Briain^[6] respectively favoured the obscure medieval septs of Uí Cuaich and Cuachraige, though in neither case has a connection been demonstrated.