-mpi

To form the comparative, follow these stem rules:

• Consonant Gradation: The -mpi suffix triggers the weak grade in basic vowel-stem adjectives (e.g., halpa → halvempi, märkä → märempi). For adjectives ending in a consonant, they use their strong vowel stem before adding -mpi (e.g., lämmin → lämpimämpi, hapan → happamampi). Note that pitkä (long) is irregular, becoming pitempi or pidempi.
• Vowel Changes (Short Words): In 2-syllable adjectives ending in -a/-ä, the final vowel changes to -e- (e.g., vanha → vanhempi, kylmä → kylmempi). A notable exception is kiva, which can be either kivempi or kivampi.
• Stable Vowels: Adjectives ending in -o, -u, -y, or -i (modern loans) do not change their final vowel (e.g., hieno → hienompi, siisti → siistimpi).
• Old Native Words in -i: For older native adjectives ending in -i, the final vowel changes to -e- before adding the suffix (e.g., suuri → suurempi). However, old words ending in -si use their 't'-stem, which undergoes consonant gradation to 'd' before -mpi, whose consonant cluster closes the preceding stem syllable. Therefore, -si changes to -de- (e.g., uusi → uudempi, tosi → todempi).
• Words in -e: Adjectives ending in -e add an extra -e- before the suffix (e.g., tuore → tuoreempi).
• Words in -nen: Adjectives ending in -nen change to -se- before adding the suffix (e.g., punainen → punaisempi).
• Consonant Stems (-as/-äs, -is, -ton/-tön): These use their strong vowel stem before adding -mpi. For example: rakas → rakkaampi, kallis → kalliimpi, työtön → työttömämpi.
• Words in -ut/-yt: Adjectives of the ohut : ohuen and lyhyt : lyhyen classes use their e-bearing vowel stems: ohue- → ohuempi, lyhye- → lyhyempi. Lyhempi is also standard. This is not a rule for every word ending in -ut/-yt: participles use their own stems, as in väsynyt → väsyneempi.
• Irregular: The adjective hyvä (good) becomes parempi (better).
• Suffix Gradation: The -mpi suffix itself undergoes consonant gradation. It is -mpi in the nominative, and weakens to -mma-/-mmä- in closed cases like the genitive or inessive (e.g., isomman, isommassa). However, it remains strong as -mpa-/-mpä- in the partitive (isompaa) and illative (isompaan).

Comparison Methods:
1. Using kuin (than): Talo on isompi kuin tuo. (The house is bigger than that.)
2. Using the partitive comparison: Talo on tuota isompi. (The house is bigger than that.)

Longer Adjectives
In adjectives with three or more syllables, final a/ä normally remains: mukava → mukavampi, terävä → terävämpi. A compound follows the pattern of its final adjective component, so total syllable count alone is not enough. Standard kiva permits both kivempi and kivampi, and hapan permits happamampi and happamempi.