Possessive pronoun agreement

For 1st and 2nd person pronouns (my, your, our), the ending changes to match the gender, number, and case of the noun being owned. Note the critical distinction for 'your': use tvůj when speaking informally to one person, and váš when speaking formally to one person or addressing multiple people. For 'our', use náš. If a man and a woman both talk about their family and belongings, they both say můj bratr because bratr is masculine, moje sestra because sestra is feminine, and naše auto (our car) because auto is neuter. This agreement also applies to plural nouns, such as moji přátelé (my friends) or naše děti (our children). For 3rd person pronouns, the base word depends on the owner: jeho (his/its), její (her), and jejich (their). While jeho and jejich never change their form, její declines like a soft adjective to agree with the noun being owned.

Important Nuances:

• The reflexive svůj: If the owner is also the subject of the sentence, formal grammar requires you to use svůj instead of the regular possessive. While this is strictly mandatory for the 3rd person to avoid changing the meaning to 'someone else's' (e.g., Petr miluje svou ženu = Petr loves his own wife), in everyday spoken Czech, native speakers frequently just use můj and tvůj for the 1st and 2nd person (e.g., Já vidím mého/svého bratra).
• Soft endings for náš and váš: Because the stems of náš (our) and váš (your) end in the soft consonant 'š', they take soft endings when declined (e.g., našeho, našemu), unlike the hard/mixed endings of můj, tvůj, and svůj.
• The její shortcut: Because její declines like a soft adjective, it never changes its form when modifying a feminine singular noun. Whether it's the subject, object, or after a preposition, it remains the same (e.g., její sestra, bez její sestry, vidím její sestru). However, remember that it does change to agree with masculine and neuter nouns (e.g., vidím jejího bratra, jedu jejím autem).
• Long vs. Short forms: For můj, tvůj, svůj, you will see long forms (moje, tvoje, svoje) in everyday standard Czech. In formal or literary contexts, you will see short forms for feminine (má, tvá, svá) and neuter (mé, tvé, své). For masculine and neuter nouns, this long/short distinction only exists in the nominative, accusative, and vocative cases. For feminine nouns, however, this duality exists in all cases (e.g., the feminine accusative short mou vs. long moji). Unlike these, the plural pronouns náš and váš do not have short and long forms.
• Spelling traps: Be careful not to confuse jejich (their, which is indeclinable and has a short 'i') with jejích (the declined forms of její, meaning 'her', which have a long 'í'). Also, when using the long forms of můj, tvůj, svůj for feminine singular nouns, pay attention to the final 'i'. The accusative form ends in a short 'i' (moji), but the genitive, dative, locative, and instrumental forms end in a long 'í' (mojí).
• Dropping possessives: Czechs often drop possessives entirely when ownership is obvious, especially for body parts and clothing. Instead of 'my head hurts', say bolí mě hlava.