Comparing objects, as in big, bigger, biggest is done in pretty much the same way as in English, as is saying something is very good, or very expensive, or very cold.

Saying 'very', as in 'very good' or 'very nice' is done in two ways: adding the word iontach or adding the prefix an-.

deas — nice
iontach deas — very nice
an-deas — very nice

iontach does not cause lenition in the adjective that follows it. an- does cause lenition in words beginning with a consonant, except those beginning with d, l, h, r, s, or t.

Saying 'too', as in 'too cold' or 'too expensive' is done by adding the prefix ró-.

fuar — cold
rófhuar — too cold

Adding ró- causes lenition in adjectives beginning with a consonant, except those beginning with l, n, or r.

Of course, there are a number of irregular forms in Irish, just as there are in English (like good, better, best). But, they are limited, and can easily be memorized:

beág (small)	nios lú (smaller)	is lú (smallest)
breá (fine)	nios bréatha (finer)	is bréatha (finest)
fada (long)	nios faide (longer)	is faide (longest)
furasta (easy)	nios fusa (easier)	is fusa (easiest)
maith (good)	nios fearr (better)	is fearr (best)
mór (big)	nios mó (bigger)	is mó (biggest)
olc (bad)	nios measa (worse)	is measa (worst)
te (hot)	nios teo (hotter)	is teo (hottest)