-a/-ä, -ta/-tä

The partitive is a frequent Finnish case used for objects, quantities, and some subjects and complements. It is formed by adding -a/-ä, -ta/-tä, or -tta/-ttä.

When to use it:

• Indefinite Amounts: Use it for mass nouns (uncountables) like water or coffee. Juon vettä (I drink [some] water).
• Ongoing Actions: If you are in the middle of doing something, the object is partitive. Luen kirjaa (I am reading a book).
• Negation: The direct object of a negative sentence is partitive. En osta autoa (I am not buying the car). Note: Singular count noun complements remain nominative (Tämä ei ole auto), but mass noun complements are partitive (Tämä ei ole vettä).
• Numbers: When a number (except 'yksi') is in the basic form, it requires the singular partitive. Kaksi koiraa (Two dogs).
• Verbs With Partitive Objects: Learn the object case with the verb. Alongside rakastaa (love), common patterns include auttaa ystävää (help a friend), etsiä avainta (look for a key), and odottaa bussia (wait for a bus). Do not infer this from the English meaning: ymmärrän asian (I understand the matter) has a total object, while en ymmärrä asiaa has a negative partitive object.
• Existential Sentences: In sentences expressing that an uncountable mass exists somewhere, the subject is partitive (e.g., Lasissa on vettä).
• Plural Subjects in Existential Sentences: Used when expressing that an indefinite amount of plural items exists somewhere. Pihalla on poikia (There are boys in the yard).
• Prepositions and Postpositions: Used with certain prepositions (e.g., ilman, ennen) and postpositions. Ennen joulua (Before Christmas).
• Comparisons: Used in comparisons to mean 'than'. Taloa suurempi (Bigger than a house).
• Greetings: Standard greetings (e.g., Hyvää huomenta) are almost always in the partitive because they are implicitly the object of a dropped verb.

Singular Formation Rules:

• -a/-ä: Most words ending in a single vowel (except -e). Example: talo → taloa. Note: When adding -a/-ä, the word remains in the strong grade (e.g., katu → katua).
• -ta/-tä: Words ending in a long vowel or diphthong, or a consonant. For some old Finnish words ending in -i, the ending is added to a consonant stem (e.g., vesi: vet- + -tä → vettä, kieli: kiel- + -tä → kieltä). Example: maa → maata, puhelin → puhelinta.
• -tta/-ttä: Many words ending in -e, such as the huone type. Other -e types differ: nalle → nallea. The ending is added directly to the nominative basic form. Example: huone → huonetta.
• -nen words: Words ending in -nen replace -nen with -s- before adding -ta/-tä. Example: nainen minus -nen = nai- + -s- + -ta = naista.

Always remember vowel harmony: use -a/-ta for back vowels (a, o, u) and -ä/-tä for front vowels (ä, ö, y). Words containing only neutral vowels (e, i) take the front vowel endings (-ä/-tä).

Note: The rules above apply to the singular partitive. The plural partitive exists and uses different endings (e.g., -ia/-iä, -ja/-jä, -ita/-itä) and is used for plural indefinite amounts.

Personal Pronouns
Learn these partitives as a set: minä → minua, sinä → sinua, hän → häntä, me → meitä, te → teitä, he → heitä. For example, Autan häntä (I help him/her) and En näe heitä (I do not see them). Old -i nouns also need their own stem pattern: compare vesi → vettä with ovi → ovea.