I was just wondering with the use of 'is' instead of 'tá/bíonn'. Although i see examples of it throughout the duolingo course and outside of it too, i never know when to use it other than with 'is buachaill mé' or 'is maith/fearr' and a few other examples. For example i can't understand why we should use 'is' in the phrase 'is leor sin'. Is it idiomatic? or is there a pattern. Could someone please explain when we should use 'is' instead of 'tá/bíonn' other than 'is ... mé' and 'is maith...'
Thanks in advance
The basic difference is that "is" is used in reference to permanent or intrinsic characteristics, properties, natures, etc. Thus, "is fear mé", meaning, "I am a man," describes something intrinsic about me. Similarly, 'is crann sin" (that's a tree), or "is breá an lá é" (it's a nice day). Tá/bíonn is generally for transient conditions: Tá mé go maith = I am well; bíonn athas air i gcónaí = he's always happy. If you've studied Spanish or Portuguese, it's nearly identical to the distinction between ser/estar (=is/ta, respectively).
There is an unusual construction in which "tá" can be used to express inherent properties just like "is." For example, you can say "Tá mé i mo chocaire," (I am a cook), or "Tá sé ina bhuachaill" (he is a boy). You'll recognize it as the same construction used for where one lives: "Tá mé i mo chónaí i nGaillimh" = I live in Galway.
Hope that helps.
There is an unusual construction in which "tá" can be used to express inherent properties just like "is." For example, you can say "Tá mé i mo chocaire," (I am a cook), [...]
I remember reading in the forums that "Tá mé i mo chocaire" means "I work as a cook, but I don't look myself as a cook", while "Is cocaire mé" (and maybe even "Is cocaire atá ionam", not sure) is actually "I am a cook". So, the difference between permanent and transient characteristics should apply here as well. Please, correct me if I'm wrong.
The difference between "Is" and "Tá" is basically just that "Is" is used to say you are a "thing" and "tá" is used to say you are "in a state".
Most things that seem to break this are either nouns that look like adjectives (for example there is a noun "maith" that means "a good thing") or constructions that use "being in a state" as an indirect way of saying you are a thing: e.g. Táim im dhochtúir (although the meaning of this is slightly different from Is dochtúir mé).
Permanent versus impermanent doesn't really factor into it.