The Celtic languages of the British Isles can be divided into two groups:

• BRYTHONIC: spoken in Britain, and represented today by Welsh and Cornish.
• GOIDELIC: spoken in Ireland and, eventually, Scotland. Irish Gaelic, Scots Gaelic and Manx belong to this group.

Goidelic languages are also categorised as Q-Celtic, whilst Brythonic are P-Celtic. This arises from a major difference between the groups – the substitution of a ‘p’ sound for a ‘q’ sound (i.e. a ‘hard-c’ or ‘k’ sound). For instance, the word ‘head’ is ‘ceann’ in Gaelic, ‘kione’ in Manx, but ‘pen’ in Welsh and Cornish.