Jesus is life?

Even Gaelic has its urban myths. One of them is that 'S e do bheatha supposedly is Is E do bheatha, as in He (Jesus or God) is your life. Nice try but no.

It's true that if you dig a bit further back into history, you come across dia do bheatha in Old Irish (yes, fortunately they wrote things down, so we have an instance of CuChulainn greeting Fergus with Fuit! Día do bethu, a phopa Fergus. So while this looks bit like it might be invoking anthropomorphised omnipotent beings, there's an immediate problem. Yes, it's unlikely to be the Christian pantheon because the Fianna didn't do Christianity.

Bearing in mind very similar Old Irish formulae, such as

• rotbia-su fáilte "to you will be welcome"
• rotbia in failti sunda againni "to you will be welcome here at us"

it is much more plausible that the origin of this phrase was rotbia de bethu "to you will be life". ro-t·bia being, by the way:

• ro, in Old Irish this is a preverb (a particle which may go before a verb), a form of do meaning "to(wards"
• -t- (a marker for the second person "you"), so it's a little bit like having the modern dhut "to(wards) you" sitting before the verb. But it's not, before you go down that route, dhut per se, because that was duit/dait in Old Irish
• -bia which is the 3rd person singular future of the verb "be" (think of modern bi(dh).

Over time, this would change quite regularly:

1. rotbia de bethu drops the preverb ro leaving us with
2. tbia de bethu which immediately simplifies tb- to just t- and weakens and slenderises it, giving us
3. dia de bethu, which now falls prey to that ancient confusion between de & do, giving us
4. día do bheatha which is the re-analysed to
5. dé do bheatha, further reduced to
6. sé do bheatha and the re-analysed again as
7. 's e do bheatha.

This also explains neatly, by the way, why this seemingly is ungrammatical i.e. in reference to beatha, you would expect Is í do bheatha rather than Is é.