Genitive Possession

1. The Word Order Rule
In English, we say 'The neighbor's car'. In Polish, the order is flipped for nouns: Samochód sąsiada (Car [of] neighbor). The possessor noun normally follows the noun it modifies; marked emphasis can change this order. Note that possessive adjectives (like mój) still come before the noun.

2. How to Form It
You must decline the possessor noun using Genitive Singular or Genitive Plural endings:

• Masculine Animate: Ends in -a (brat → brata).
• Masculine Inanimate: Ends in -u (dom → domu) or -a (for many categories like tools, fruits, and months).
• Masculine Nouns in -a: Nouns like mężczyzna or tata decline like feminine nouns in the singular, taking -y or -i (mężczyzna → mężczyzny).
• Feminine: Ends in -y or -i (mama → mamy). Feminine nouns ending in a consonant also take -y or -i (noc → nocy, rzecz → rzeczy).
• Neuter: Most end in -a (dziecko → dziecka). For nouns ending in -ę, the stem palatalizes to -ęci- or -ieni- before adding -a (zwierzę → zwierzęcia, imię → imienia). Nouns in -um do not change in the singular (muzeum → muzeum), but decline regularly in the plural (muzeów).
• Masculine Plural: Ends in -ów (sąsiedzi → sąsiadów) or -i/-y for soft-stem nouns (goście → gości).
• Feminine/Neuter Plural: Often uses a Zero Ending (kobiety → kobiet). However, feminine nouns ending in a consonant take -i or -y in the genitive plural (rzecz → rzeczy, noc → nocy). If dropping the final vowel leaves an awkward consonant cluster, a 'mobile e' is inserted (matka → matek, okno → okien).

3. Adjective Agreement
If the possessor has an adjective, it must also be in the genitive case. Use -ego for masculine/neuter singular, -ej for feminine singular, and -ych or -ich for all plural nouns. Example: samochód moich sąsiadów (the car of my neighbors).

4. Specific vs. General
Use this pattern for specific owners (przystanek autobusu - the stop of a specific bus). For general categories, Polish uses Relational Adjectives which follow the noun (przystanek autobusowy - bus stop). Unlike descriptive adjectives (czerwony dom), relational adjectives defining a type usually come after the noun.

5. Other Uses
Note that the Genitive case is also mandatory in negated sentences (e.g., Nie mam samochodu) and after certain prepositions like od, do, and z (only when z means 'from/out of', e.g., z domu; when it means 'with', it takes the Instrumental case, e.g., z sąsiadem).

Two Independent Case Roles: The possessed noun changes with its role in the sentence; its possessor stays genitive. Compare To jest książka Anny (This is Anna’s book), Widzę książkę Anny (I see Anna’s book), and Mówię o książce Anny (I am talking about Anna’s book). Książka becomes książkę or książce; Anny still identifies the owner. An adjective describing Anna also remains genitive.