-i / -y

The past-tense plural endings attach to the past participle (the l-form of the verb). Here are the standard rules:

• Masculine animate: ends in -i (e.g., muži dělali)
• Masculine inanimate: ends in -y (e.g., stroje dělaly)
• Feminine: ends in -y (e.g., ženy dělaly)
• Neuter: ends in -a (e.g., města dělala)

Compound Subjects (Mixed Groups)
When a subject consists of multiple nouns connected by "and" (a), follow this hierarchy:
Masculine Animate > Masculine Inanimate / Feminine > Neuter

If there is at least one masculine animate noun in the subject, the verb takes -i (Muži a ženy přišli). If there are no masculine animate nouns, but at least one masculine inanimate or feminine noun, it takes -y.

Verb Preceding the Subject
If the verb comes before a compound subject, it can agree with the closest noun (e.g., Do místnosti vešly ženy a muži).

First and Second Person Plural (My / Vy)
When using my (we) or vy (you plural), the ending depends on the group's composition. A mixed group including at least one male takes -i (my jsme dělali). A group of only females takes -y (my jsme dělaly). Crucially, when using formal vy to address a single person, the past participle remains singular to match the person's natural gender (e.g., Pane Nováku, vy jste to dělal? or Paní Nováková, vy jste to dělala?).

Important Exceptions

• Děti, oči, uši: These nouns are neuter in the singular but behave as feminine in the plural, taking -y (děti si hrály).
• Rodiče, lidičky, and live koně: These take the masculine animate ending -i (rodiče přijeli, koně běželi). However, if koně refers to inanimate objects (like wooden horses or chess knights), it takes -y (šachové koně chyběly).
• Dny / dni: The plural forms of den (day) take the masculine inanimate ending -y (dny ubíhaly).

Common Learner Traps

• Grammatical vs. Biological Animacy: Animacy is a grammatical category. Grammatically animate but biologically inanimate nouns take -i (sněhuláci roztáli), while grammatically inanimate nouns representing groups of people take -y (davy lidí proudily).
• Unexpressed 'They': When the subject 'they' is dropped and refers to people in general (like 'they said on the radio'), the default ending is masculine animate -i (Hlásili to v rádiu).
• Collective Nouns: The verb strictly agrees with the grammatical gender of the head noun, not the people it describes. For example, skupina mužů (a group of men) takes the feminine singular ending -a because skupina is a feminine singular noun (Skupina mužů čekala).
• Quantifiers like tisíce or miliony: When using words like tisíce (thousands) or miliony (millions) with people (e.g., tisíce lidí), the verb agrees with the quantifier itself. Since tisíc is a masculine inanimate noun, the verb takes -y (Tisíce lidí přišly), not -i.
• The Neuter Trap: Two singular neuter nouns combined (e.g., kotě a štěně - a kitten and a puppy) take -y, not -a! The -a ending is strictly reserved for actual plural neuter nouns (e.g., koťata a štěňata si hrála).

Spoken vs. Written Czech
In modern Czech pronunciation, -i and -y sound exactly the same (as a short /ɪ/). In everyday spoken Common Czech, the neuter plural ending -a is often dropped and replaced by this same /ɪ/ sound. However, in writing, the distinction between -i, -y, and -a is strictly maintained. Writing kluci byly is considered a severe spelling mistake!