These notes were posted on Gaeilge-B on 28 Deireadh Fomhair, 2002, by Dorothy Milne.

There are a variety of 'is' constructions. You need to learn them a bit at a time. Some people concentrate on learning one IS sentence type at a time .. getting the 'model' for one type fixed really well in their mind before moving on to another.

They are complex!

-1- The first distinction a student usually has to learn is the difference between 'is' and 'tá' when saying X is Y. So:
Is cupán é sin. That is a cup.
Tá an cupán go deas. The cup is nice.

-2- But another use of 'IS' is to 'front' the part of the sentence you want to emphasize. So:
Chonaic mé bláthanna inné. I saw flowers yesterday.
You can use 'is' to say:
Is mise a chonaic bláthanna inné. It's I who saw flowers yesterday.
Is bláthanna a chonaic mé inné. It's flowers that I saw yesterday.
Is inné a chonaic mé bláthanna. It's yesterday that I saw flowers.

-3- Now with adjectives - Is lá breá é. It's a fine day.
This would be a good IS sentence, but Irish prefers to take this sentence and modify it to read:
Is breá an lá é. It's fine (that) the day (is) .
Is deas an cóta é. Is nice (that) the coat is... It's a nice coat.
The structure of this sentence is a bit opaque unless you are a linguistics- or grammar- starved individual (like quite a few of us are on this list (:-)

But never mind understanding the structure. I think you can get a 'feel' for this Is + adjective sentence type (Is deas an cóta é) by comparing it to the other fronted sentences. Then learn the pattern.

This adjective pattern is often seen with 'nach':
Nach deas an cóta é ! Isn't (it) nice that the coat is! - Isn't it a nice coat!
Nach mór an seomra é seo. Isn't this a big room! Etc.

Hope this helps, Doireann