Expressing the Agent in the Passive

A passive sentence promotes the thing acted upon to subject — the house was destroyed, the book was written — and that immediately raises a question English answers with one little word: by whom? English bolts on a by-phrase: destroyed *by fire, written **by a famous author. Czech does it with no preposition at all. It takes the doer, the *agent, and drops it straight into the instrumental case: zničen požárem, napsána slavným autorem. There is no word for "by" — the case ending alone carries the whole meaning. This is the construction's special power, and it is available only in the participial passive (být + a passive participle); the reflexive se-passive cannot name an agent at all.

The core rule: the agent goes in the instrumental

The instrumental — sedmý pád, the seventh case — already marks the means by which something is done (píšu perem "I write with a pen"; see the instrumental of means). Naming the agent of a passive is the same idea taken one step further: the agent is the means by which the action came about. So Czech reuses the case it already has. Where English needs by, Czech needs only the ending.

In each case the by-phrase of English collapses into a single inflected word. Požárem is not "fire + by"; it is oheň/požár wearing its instrumental ending, and that ending is the "by."

The participle agrees; the agent inflects

The passive participle (zničen, napsán, rozbit) agrees with the subject in gender and number, exactly like a short adjective. The agent, separately, takes the instrumental. Keep the two jobs apart in your head: the participle looks back at what was acted on; the instrumental noun names who did it.

For the full set of participle endings and how the long attributive form differs from this short predicative one, see the passive participle as adjective.

Personal agents: instrumental is standard, od + genitive is marked

For an inanimate force or means (fire, lightning, a ball, water), the instrumental is the only natural choice. For a personal, animate agent (an author, a builder, a committee), the instrumental is still the standard, literary, neutral option — and the one to default to.

There is, however, a second option that surfaces with personal agents in some styles: od + genitive. Byl pochválen od učitele "he was praised by the teacher." Historically od (literally "from") frames the agent as a source the action comes from, and it leans (informal) or marked. Czech grammarians have long flagged od + genitive as a colloquial or stylistically lower variant of the plain instrumental, and careful writers prefer the bare instrumental in formal prose.

When you have no agent to name: drop to the reflexive passive

Naming the agent is the participial passive's whole reason to exist. If you do not know, or do not care, who did it — which is most of the time — Czech overwhelmingly prefers the agentless reflexive passive with se instead. The reflexive passive cannot take an instrumental agent; that is precisely the division of labour between the two passives.

So the choice is mechanical: agent named → participial passive + instrumental; agent unknown or irrelevant → reflexive se. The full comparison of the two passives, with the decision table, lives on the participial-versus-reflexive passive page.

Aspect shapes the agent sentence too

The participial passive pairs most naturally with perfective verbs, where the participle reports a finished, bounded event with an accountable doer: byl postaven, byla napsána, byl zatčen. An imperfective participle (je stavěn, je čten) describes an ongoing process, and is where naming an agent feels most like a deliberate, written choice.

How this differs from English

English keeps the agent last and flags it with by: The window was broken by a ball. Czech keeps the agent's case ending doing the work and is far freer about word order, because the instrumental ending labels the agent no matter where it sits. Míčem bylo rozbito okno and Okno bylo rozbito míčem both mean "the window was broken by a ball"; the instrumental míčem is unmistakably the agent in either order.

A second difference is frequency. English uses agented passives constantly (the report was written by the committee). Czech, given the choice, often prefers a plain active sentence (zprávu napsal výbor "the committee wrote the report"), reserving the agented passive for formal, written, or topic-shifting contexts. Knowing the construction is essential for reading news and contracts; over-using it in speech sounds stiff.

Common mistakes

Key takeaways

• In a participial passive, the agent goes in the bare instrumental — no preposition. English by is just the case ending: zničen požárem, napsána autorem.
• The participle agrees with the subject in gender and number; the agent inflects for the instrumental. Keep the two jobs separate.
• Inanimate agent → only the instrumental. Personal agent → instrumental is the formal default; od
  • genitive exists but is marked and colloquial.
• The reflexive se-passive cannot name an agent. If you need to say who did it, switch to the participial passive or, more naturally, to the active voice.
• Default to agentless se when the doer is unknown or irrelevant — which is most of the time.