h2g2 The Hitchhiker's Guide to the Galaxy: Earth Edition

Well Irshi/Scots Gaelic/Manx and Welsh/Cornish/Breton are both forms of Celtic, in much the same way as Italian, Spanish and French are all Latin languages, and all have their origins in a common ancestor, a root celtic.

They are clasified in a veriety of ways, one being P-Celtic, Breton/Welsh/Cornish, and Q-Celtic, Irish/Scots Gaelic/Manx, where in one form the *k^w of comon, or proto-, celtic became a *p and in the other became *k. For example the 'common' celtic, or proto-celtic, verb Krin, meaning 'to buy' became 'pryn' in welsh and 'cren' in old Irish.

They could, really, be classified as dialect forms of 'Celtic' in the same way that Italian, Spanish and French could be deemed to be Latin Dialects. Therefore to call one an ugly language and another beautiful demonstrates an ignorance of this common heritage and relationship, especially as the Q-Celtic family of languages appears to be the least corrupted of these two forms.

Q-Celtic and P-Celtic?

Goeidic and Brythonic are the terms I've seen, meaning (as far as I can determine) the same thing.

TRiG.

No, they are quite similar though. Goidelic languages are Irish, Scots Irish, Manx. The Brythonic languages are Welsh, Breton, Cornish, Cumbric, the hypothetical Ivernic and maybe Pictish. As a very basic difference, generally the Brythonic, or at least their modern ancestors, have a large amount of words of Latin origin in them.

But The Insular Celtic versus Continental Celtic is a different theory to the P-Celtic Q-Celtic one.