pitää

The necessive use of pitää is one of the most frequent ways to express obligation in Finnish. While täytyy is the neutral standard for 'must', pitää is more common in spoken Finnish and can lean slightly softer toward 'ought to' or 'should'. It follows three strict rules:

• The Subject: The person who has the obligation must be in the genitive case (ending in -n for singular, or endings like -en or -iden for plural).
• The Verb 'pitää': This verb is frozen in the 3rd person singular. It does not change for person (I, you, we, etc.), but it does change for tense. For example, in the present tense it is always pitää, and in the past tense it is always piti. To express 'should' or 'ought to', the conditional form pitäisi is very commonly used (e.g., Minun pitäisi opiskella - I should study).
• The Main Action: The action that must be done is in the 1st infinitive (the dictionary form).

The Object Rule:
A unique feature of necessive sentences is how the object behaves. If you must do something to a 'whole' item, singular regular nouns take the nominative case (no -n ending). For example: Minun pitää ostaa auto (I have to buy a car). Plural total objects take the nominative plural ending (-t): Minun pitää ostaa autot (I have to buy the cars). Personal pronouns and kuka have special -t total-object forms: Kenet minun pitää kutsua? (Whom must I invite?). Compare: Minun pitää nähdä sinut (I have to see you). If the main action is a partitive verb or the object is a mass/uncountable noun, the object remains in the partitive case even in affirmative necessive sentences: Minun pitää juoda vettä (I have to drink water). Crucially, in negative necessive sentences, the object must always be in the partitive case: Minun ei pidä ostaa autoa (I should not buy a car).

Negation and Alternatives:
When you want to say someone 'should not' do something, use ei pidä. This is used for strong advice. If you want to express a strict prohibition ('must not' or 'is not allowed'), use the negative of saada (ei saa). Note that switching to ei saa means dropping the genitive subject and using the nominative (e.g., Minä en saa... - I must not...). If you simply mean 'don't have to', use ei tarvitse, which retains the genitive subject (e.g., Minun ei tarvitse mennä - I don't have to go). For the strongest level of obligation ('to be forced to' or 'to have no choice'), use on pakko, which also takes a genitive subject (e.g., Minun on pakko mennä - I have to go).

Warning: Do not confuse the necessive pitää with the verb pitää meaning 'to like'. When meaning 'to like', the subject is in the nominative case and the complement is in the elative case (ending in -sta/-stä); this is not a grammatical object, e.g., Minä pidän kahvista (I like coffee).