"He made a thief (out) of himself". Was just wondering earlier about the 'de' part of this. Why is it not 'dó' féin?

Any ideas le bhur dtoil?

"de" can mean "of"
"do" generally means "for"

You could say "Rinne sé císte milis dó féin" He made a sweet cake for himself (alone).

and "rinne sé bosca d'adhmad" He made a box [out] of timber."

I'm okay with the difference between de and do. With rinne sé gadaí de féin it's more that I was wondering why there wasn't de + é = dó. You can't write Rinne sé gadaí 'de é' féin, so I guess I'm really trying to figure out why the pronoun é hasn't been compounded with de here. It's left out. It's the first time I've seen that.

I think the word "féin" is functioning as a pronoun here.

Ó Dónaill introduces it with: "emphatic and reflexive adjective and pronoun" Page 533

Anyway "de" is the third person masculine of the prepositional pronoun "díom"

de gives
díom, díot, de, di, dinn, díbh, díobh. There's your "de" = "de + é"

do gives
dom, duit, dó, di (pronounced "daoi" in my dialect), dúinn, díbh (pronounced "daoibh" in my dialect), dóibh.

With "de" all the "ds" are slender.

With "do" (in North Mayo) all the "ds" are broad.

Now let's have fun: what of other dialects? I know that in some dialects they don't even have these words.

My other reply went amú. Was just saying thanks, I actually had thought that de and do shared the same 3rd person masculine : dó. So that's where I was going wrong. I've had that one wrong all this time, so it's a breakthrough :)