Adjectives Agree with the Noun

Finnish adjectives act like mirrors for the nouns they modify, provided they are placed directly before the noun (attributive position). This agreement happens in two ways:

1. Case Agreement: Adjectives agree with the noun in its case. If the noun is in the partitive, genitive, or any local case, the adjective takes that same case.

2. Number Agreement: If the noun is plural, the adjective must also be plural (e.g., isot talot - big houses).

Important Rules:

• Stacked Adjectives: If you use multiple adjectives, every single one must agree with the noun (e.g., isossa punaisessa talossa - in the big red house).
• Comparison: Both the comparative and superlative forms follow these same agreement rules.
• The Number Rule: When using cardinal numbers greater than one or zero (including 0, 2, 21, 31, etc., but excluding 1) in the basic form, both the adjective and the noun shift to the partitive singular (e.g., kaksi isoa taloa - two big houses, nolla isoa taloa - zero big houses). If the phrase takes any other case (such as the genitive, partitive, local, or role cases), the number, adjective, and noun all agree in that case and remain in the singular (e.g., kahdessa isossa talossa - in two big houses). Note that with plural-only nouns (e.g., sakset, häät), the number, adjective, and noun all take the plural form (e.g., kahdet isot sakset - two big scissors).
• Total Objects: The adjective mirrors the object case, whether the grammar dictates it look like the nominative (Osta iso talo! - Buy a big house!) or the genitive (Ostan ison talon - I will buy a big house).
• -inen Adjectives: Adjectives ending in -inen (like punainen) change their stem to -ise- before adding most case endings (e.g., punaisessa talossa - in the red house), but the partitive singular uses the stem -is- (e.g., punaista - red).
• Indeclinable Adjectives: A few adjectives like ensi (next), viime (last), koko (whole), pikku (little), and eri (different) never change their form.
• Predicative Adjectives: When an adjective follows the verb 'to be' (olla + predicate adjective), it describes the subject. If the subject is singular and countable, the adjective is in the nominative (Talo on iso - The house is big). If the subject is plural, the adjective is usually in the partitive plural (Talot ovat isoja - The houses are big), but specific bounded sets or natural pairs can take the nominative plural (Kengät ovat uudet - The shoes are new). If the subject is an uncountable mass noun, the adjective is in the partitive singular (Maito on kylmää - The milk is cold).
• Independent Changes: Adjectives and nouns apply vowel harmony and consonant gradation completely independently of one another (e.g., märkä + ruoho in the inessive becomes märässä ruohossa - in the wet grass).
• Possessive Suffixes: When an adjective modifies a noun with a possessive suffix, the adjective agrees in case but the possessive suffix attaches only to the noun, not the adjective (e.g., iso taloni - my big house, isossa talossani - in my big house).

Partitive Objects Agree Too
An ongoing event or indefinite quantity can require partitive in both words: Luen mielenkiintoista kirjaa (I am reading an interesting book). Ordinary negation does the same: En osta isoa taloa. Agreement follows the selected case; it does not determine whether the clause needs a total or partitive object.