Adjective Agreement
In Finnish, adjectives are team players: they must match the noun they describe in both case and number. This is called adjective agreement.
If your object is in the partitive case—for example, because it is a mass noun like water or coffee, or because the sentence is negative—any adjective describing that object must also take a partitive ending.
Adjectives Ending in a Vowel
For most adjectives that end in a basic vowel, forming the partitive is just like forming it for nouns: simply add -a or -ä (following vowel harmony rules).
Adjectives Ending in -nen
Many common Finnish adjectives end in -nen, including several colors. To make these partitive, drop the -nen and add -ista (or -istä).
For example, punainen (red) becomes punaista, and valkoinen (white) becomes valkoista.
Adjectives Ending in -e or a Consonant
Adjectives ending in -e behave a little differently. To form the partitive, you add -tta or -ttä. For example, tuore (fresh) becomes tuoretta.
If an adjective ends in a consonant, such as -s, you add -ta or -tä. For example, puhdas (clean) becomes puhdasta.
