Comparatives With Endings

When an adjective is in the comparative degree, it doesn't just stay as -mpi. If the noun it describes is in a case like the Genitive, Inessive, or Adessive, the adjective must match.

1. The Root Vowel Change
Before adding the -mpi suffix, two-syllable adjectives ending in a single -a/-ä change that vowel to -e- (e.g., vanha (old) → vanhempi, kylmä (cold) → kylmempi). However, adjectives with three or more syllables keep their -a/-ä (e.g., mukava → mukavampi). This excludes adjectives with double vowels like vapaa. Both kivempi and kivampi are accepted in standard Finnish; the latter is an accepted exception to the usual two-syllable vowel change.

2. The Two Stems
The -mpi ending is used for the Nominative Singular (and the Accusative Singular when it is identical to the nominative). For all other cases, the suffix changes into one of two stems:

• Strong Stem (-mpa-/-mpä-): Used for the Partitive Singular (-a/-ä), Illative Singular (-an/-än), and Essive Singular (-na). The corresponding plural strong stem has -mpi-, because a/ä drops before plural i: isompia, isompien, isompiin, isompina. Example: isompi → isompaa.
• Weak Stem (-mma-/-mmä-): Used for most other cases, including the Nominative Plural (-t), which is also the plural total-object form (Valitsin isommat), Genitive Singular (-n), Accusative Singular (-n), Inessive (-ssa), Adessive (-lla), Translative (-ksi), Elative (-sta), Ablative (-lta), and Allative (-lle). Example: isompi → isommat, isommassa, isommaksi.

3. Consonant Gradation
The change from -mpi to -mma- is a form of consonant gradation (mp → mm). This usually happens when the case ending closes the syllable. However, the Illative is a major exception: even though the syllable is closed (e.g., isompaan, isompiin), it always uses the strong stem.

4. Plural Formation
In the plural, the marker -i- is added to the stem. The stem vowel -a/-ä drops before the plural -i- in the i-plural cases. Nominative plural instead adds t to the singular weak stem: isommat. For example, in the Partitive Plural isompia, the final -a is actually the partitive case ending, not the stem vowel.

5. Vowel Harmony
Always remember vowel harmony. If the root word has back vowels (a, o, u), use -mpa-/-mma-. If it has front vowels (y, ä, ö), use -mpä-/-mmä-. If a word contains only neutral vowels (e, i), it must take the front vowel endings (e.g., pieni → pienempi → pienemmässä). Example: kylmemmässä (in a colder...).

6. Irregularities
Some adjectives have irregular comparatives, such as hyvä (good) → parempi (better) and pitkä (long) → pidempi / pitempi. These still follow the same inflection rules: paremmassa, parempaa, etc.

Other Adjective Stems
Add -mpi to the appropriate vowel stem: iloinen → iloise- → iloisempi, rakas → rakkaa- → rakkaampi, and kaunis → kaunii- → kauniimpi. Then inflect the comparative itself: iloisemman, rakkaammalle, kauniimpia. The original adjective’s ending is not simply followed by -mpi.