Old Celtic language

The Proto-Celtic language, also called Common Celtic, is the reconstructed ancestor language of all the known Celtic languages. Its lexis can be confidently reconstructed on the basis of the comparative method of historical linguistics. As Celtic is a branch of the Indo-European language family, Proto-Celtic is a descendant of the Proto-Indo-European language. According to one theory, Celtic may be closest to the Italic languages, which together form an Italo-Celtic branch. The earliest archaeological culture that may justifiably be considered as Proto-Celtic is the Late Bronze Age Urnfield culture of Central Europe from the last quarter of the second millennium BC. By the Iron Age Hallstatt culture of around 800 BC, these people had become fully Celtic.

The reconstruction of Proto-Celtic is currently being undertaken. While Continental Celtic presents much substantiation for its phonology, and some for morphology, recorded material is too scanty to allow a secure reconstruction of syntax. Although some complete sentences are recorded in Gaulish and Celtiberian, the oldest Celtic literature is found in Old Irish.

The phonological changes from Proto-Indo-European to Proto-Celtic may be summarised as follows. The changes are roughly in chronological order, with changes that operate on the outcome of earlier ones appearing later in the list.

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