Dom and liom, what’s the difference?

There is a certain copula construction which most grammars for learners do not concentrate enough upon, and that is the one where we have:

COPULA + NOUN/ADJECTIVE + PREPOSITION DO OR LE

Usual examples of this constructions are:

is dóigh liom “it is my opinion, I think”

is maith liom “I like”

is fearr liom “I like better, I prefer”

is maith dom “it is good for me”

is fearr dom “it is better for me”

is féidir liom “I can” (I am able to, I feel like doing it etc.)

is féidir dom “I can (there is no reason why not)”

Note that there is an important difference between le and do in these constructions: where both can be used with a certain noun/adjective following is, the le construction refers to something subjective or personal, but the do construction refers to objective external circumstances. I found this (here standardized) example in Seán Bán Mac Meanman’s collected works:

Ní haithríoch leat, ach is aithríoch duit!

The dictionary translates the adjective aithríoch as “penitent”, but I’d say this example means “you have no regrets (i.e. you don’t feel so, subjectively), but you shoud have (i.e. you have objective reasons to feel regret)!” This is as good an illustration of the difference between le and do in this construction as any.