Degrees of comparison are expressed by means of suffixes, e.g. froai, froai-er, froai-st ‘nice, nicer, nicest’. Traditionally, these suffixes are treated as inflectional suffixes, because comparatives and superlatives do not create new dictionary lemmas.

Degemination of the fricative takes place in the superlative optionally: wies, wiezer, wiezest or wiest ‘wise, wiser, wisest’. A schwa can also be insterted after a stem ending in -t or -d: leet, leter, leetst or letetst ‘late, later, latest’, bekoand, bekoander, bekoandst or bekoandest ‘well-known, better-known, best-known’. Adjectival stems ending in /r/ are generally followed by an inserted /d/ in the comparative: roar, roarder, roarst ‘strange, stranger, strangest’ and kloor, kloorder, kloorst ‘clear, clearer, clearest.

Irregular comparative and superlative forms will be discussed below (3.2.3.2).

Attributively used comparatives and superlatives behave like positive adjectives as for case, gender and number inflection: ’n tjukker Bouk ‘a thicker book’, dät tjukste Bouk ‘the thickest book’.

Predicatively used comparatives also behave like positive adjectives in that respect, e.g.: hie waas oarich junger as iek ‘he was quite a bit younger than I’.

Predicatively used superlatives can be formed with ap ‘t [A]-ste or am [A]-sten, where [A] is an adjective(cf. German: am höchsten). This construction expresses the idea that some entity has reached its highest degree of some quality. In this type of sentences, a nominalised superlative has become part of a metaphorical prepositional phrase historically, although the construction as a whole is now completely grammaticalised.

Another predicative construction involves attributively used superlative adjectives integrated into a copular sentence. This construction tells the hearer that some entity exceeds all other relevant entities in some quality.

Die eerste Räid is die bääste. ‘The first advice is the best.’ (Compare: ‘n eerdelken Räid is am bäästen ‘an honest advice is preferable’.) Kiew is ju grotste Stääd, ju Thorolf jemoals blouked hät ‘Kiew is the largest city that Thorolf has ever seen’.

Periphrastic superlatives are not found in sources predating the twenty-first century and are not generally accepted. They do however occur in some recent Wikipedia texts (written by non-native speakers).

Native speakers tend to reject such periphrastic superlatives. Die minst bekoande Skrieuwer ‘the least well-known writer’ is more acceptable to them.

Comparatives and superlatives can be used in an absolute sense:

Some adjectives show deviating degrees of comparison, caused by either phonological adjustments or supplementation.

There are several groups of adjectives with phonologically altered comparatives and superlatives. The overview below is incomplete and only meant to be illustrative.

The curious type of paradigms represented by groot – gratter – grootst, klouk – klokker – kloukst (etc.) is triggered by phonological processes in late Old Frisian. The phonologically long vowel in grāt ‘large’ became shortened in the comparative. Hence, the comparative form gratter escaped the early modern transition from long /aː/ to long /oː/, to which groot and grootst were subjected. In the spoken language of today, the cross-linguistically usual parallellism between comparative and superlative adjective stems is often restored: groot, gratter, gratst.

Comparative forms like surrer ‘sourer’ and jurrer ‘more expensive’ are characterised by historically ‘restored’ -er endings (surrer < Old Frisian surre < reconstructed *surere). The comparative forms ending in -e (e.g. surre, durre) are still in use: ju fuul jurre Holtkole ‘the much more expensive charcoal’.

A few adjectives show supplementary forms in their degrees of comparison.

The comparative eer is used in the fixed expression ere Liede ‘former generations’.