i/y in Grammatical Endings

Most learners meet the Czech i/y problem as a vocabulary chore: the dreaded vyjmenovaná slova, the lists of root words you simply have to memorise as taking y (být, mýt, jazyk…). But there is a second, completely different i/y problem, and it is the one that keeps catching people out long after the lists are learned: the i or y in a word's ending. Here nothing is memorised. The choice is computed from grammar — from the noun's gender and animacy, from the case, from which subject a past-tense verb agrees with. Get the grammar right and the spelling falls out automatically; get it wrong and you misspell a word you "know" perfectly. This page shows where endings choose i versus y, and why it is a rule, not a list.

Two completely different i/y problems

Keep these apart, because they are solved in opposite ways:

The root problem is about which of two homophones you mean — byl ("he was") and bil ("he beat") sound identical, and only the memorised root tells them apart. The ending problem is not about homophones at all: hrady and muži are different words with different endings, and the y versus i is just the regular spelling that their grammar demands. This page is entirely about the second kind.

Noun plurals: -y, -e, or -i

The nominative plural of a noun chooses its vowel by declension type, which in the masculine also depends on animacy — whether the noun denotes something alive.

• Hard masculine inanimate nouns (the hrad type) take -y: hrad → hrady, strom → stromy, stůl → stoly, les → lesy.
• Soft masculine nouns (the stroj type) take -e: stroj → stroje, pokoj → pokoje, klíč → klíče.
• Hard masculine animate nouns take -i, and the -i softens the consonant before it: student → studenti, kluk → kluci (k→c), pták → ptáci, pes → psi, doktor → doktoři (r→ř).

So the very same hard ending splits on a single question — is it alive? — and the answer is spelled into the vowel: dead things get -y, living masculine beings get -i.

Feminine and neuter plurals follow the same logic from their own paradigms — the hard feminine žena takes -y (ženy, dívky, knihy), exactly like hrad. The full decision tree for the masculine plural lives on Choosing -i vs -y Plural Endings.

The big one: past-tense agreement (shoda přísudku)

This is where the ending i/y matters most, and where even native speakers make mistakes. The Czech past tense uses an l-participle that agrees with its subject in gender and number — and in the plural, the agreement is spelled entirely through the i/y/a of the ending. One and the same verb is written three different ways depending on what the subject is:

Read that table as a single principle: the verb's spelling is decided not by the verb but by the subject's gender. Psali / psaly / psala are the same word, "they wrote", written for a masculine-animate, a feminine-or-inanimate, and a neuter subject in turn. The neuter ending is -a, never to be lumped in with the -y row — that is a separate, third shape.

The cleanest demonstration is a single verb across three subjects that all mean roughly "the kids":

That third example is the proof that it is grammatical gender, not real-world sex, that counts: děvčata means "girls", yet it is a neuter noun, so its verb takes neuter -a. The meaning is female; the spelling is neuter. You cannot reason from "girls are female, so -y" — you reason from the noun's gender class.

Inanimate masculines side with the feminine, which surprises people: hrady ("castles") is masculine, but because it is not alive, its verb takes -y, the same ending feminine subjects use.

When a plural subject mixes genders, the masculine-animate -i wins if even one masculine-animate person is included: Petr a Jana přišli ("Petr and Jana came", -i, because of Petr). That rule has its own page, Plural Agreement: -li, -ly, -la. The general agreement system is covered in Gender and Number Agreement of the l-Participle.

Adjectives soften too

The same animacy split surfaces in hard adjectives in the masculine animate nominative plural, where the ending becomes -í and softens the stem consonant: mladý → mladí, dobrý → dobří, velký → velcí, český → čeští. For inanimate and feminine subjects the adjective keeps -é (mladé stromy, mladé ženy), and for neuter -á (mladá města). So a whole noun phrase shifts together:

The point to carry away: across nouns, adjectives, and past-tense verbs, the same grammatical signal — gender plus animacy — is spelled into the ending vowel, and it is spelled consistently. Once you can name the subject's gender, you can spell every ending in the clause without hesitation.

Common mistakes

Key takeaways

• There are two i/y problems: the root one (memorised vyjmenovaná slova) and the ending one (computed from grammar). This page is about endings.
• Noun plurals pick the vowel by class: -y hard inanimate (hrady, ženy), -e soft (stroje), -i masculine animate with softening (kluci, ptáci).
• Past-tense l-participles agree with the subject's gender: -i masculine animate (muži přišli), -y masculine inanimate and feminine (hrady stály, ženy přišly), -a neuter (auta stála).
• It is grammatical gender that counts — děvčata ("girls") is neuter, so the verb takes -a.
• The ending i/y is therefore a rule you apply, not a word you remember: name the subject's gender and the spelling is fixed.