Adjectives have three grades of comparison - the positive, comparative and superlative grade. The comparison is made by adding suffixes to the adjective stems. These suffixes are either -ar- for the comparative and -ast- for the superlative, or just -r- and -st- respectively. The suffixes -r- and -st- also i-umlaut the stem vowel.
To these suffixes are added endings. For the superlative the normal endings are used, either the strong (grimm-ast-r 'cruelest' like grimm-r 'cruel') or the weak (grimm-ast-i like grimm-i), but for the comparative only weak endings can be used, and those weak endings aren't the normal ones, but the ones that can be seen below.

with -ar- and -ast-:	with -r- and -st- and umlaut:	with either one:
· grimmr - grimmari - grimmastr 'cruel - crueler - cruelest' · hvass 'sharp' · rauðr 'red' · auðigr 'wealthy' · blóðugr 'bloody'	· fagr - fegri - fegrstr 'beautiful - more b. - most b.' · langr - lengri - lengstr 'long' · stórr - stœrri - stœrstr 'large'	· ríkr - ríkari/ríkri - ríkastr/ríkstr 'mighty - mightier - mightiest' · nýr - nýari/nýrri - nýastr 'new' · heill - heilli (/lr/ > /ll/) - heil(a)str 'whole, healthy'

Some form their comparative and superlative from other stems than the positive stem:

· góðr - betri - baztr 'good' · mikill - meiri - mestr 'big, mighty' · gamall - eldri - elztr 'old'

	sing.
nom.	lengr-i	lengr-i	lengr-a
gen. dat. acc.	lengr-a	lengr-i	lengr-a
	plur.
nom. gen.	lengr-i	lengr-i	lengr-i
dat.	lengr-um	lengr-um	lengr-um
acc.	lengr-i	lengr-i	lengr-i