These three languages diversified further at a later date. Brythonic developed into Welsh, Breton and Cornish, Gaelic into Irish, Scots Gaelic and Manx. Gaulish did not develope due to the Roman conquest of that region.

Irish or Gaelic differs from the other Celtic languages in that it uses predominantly a 'k' sound, stemming from an older 'q' sound whereas a 'p' sound is experienced in the other languages. Historians even go so far as to say that the Irish Celts had difficulty in pronouncing the letter 'p'.

One reason put forward for this is that the Irish were conservative as a result of their geographical location. It took a long time for trends to reach the island form the epicentre which was Central Europe and once they arrived they were slow to be adopted.

A notable example of this is the actual origin of the word Gael. We as Irish people traditionally call ourselves 'Gaels' or Gaoidheal/Goidel as it was spelt. Old Irish originally got this name from the Welsh who called us Gwyddel. This term meant 'backwoods people', or barbarians. This was a derogatory nickname but it has been adopted none the less.