Compound and Complex Sentences

Once you can build a single Czech sentence, the next step is joining sentences together. There are exactly two ways to do it, and Czech keeps them clearly apart. You can link two clauses of equal rank (coordination, making a souvětí souřadné, a compound sentence), or you can hang a dependent clause off a main one (subordination, making a souvětí podřadné, a complex sentence). The distinction matters in practice for one very concrete reason: it controls where the commas go. This page teaches you to tell the two apart and to punctuate each correctly.

Two clauses, two relationships

A clause is a chunk with its own verb. When a sentence has two or more clauses, they relate in one of two ways:

• Coordination — the clauses are equal partners. Neither depends on the other; you could split them into two standalone sentences. The joiners are coordinating conjunctions: a, ale, nebo, i, však, a proto, a tak.
• Subordination — one clause is the main clause and the other depends on it, filling a role like reason, time, or condition. It cannot stand alone. The joiners are subordinating conjunctions: že, protože, když, aby, kdyby, jestli, and the relative word který.

The first joins two equal actions with a (coordination). The second hangs a reason-clause off the main clause with protože (subordination). Watch the comma: it appears in the second sentence but not the first. That is the rule we are building toward.

Compound sentences (souvětí souřadné)

Here the clauses are peers. The most common coordinators are:

Each pair of clauses here could be torn apart into two independent sentences — that is the test for coordination. Pršelo. Šli jsme ven. Both stand on their own.

Complex sentences (souvětí podřadné)

Here one clause depends on the other. The dependent clause is introduced by a subordinator and answers a question about the main clause — why? when? what? on what condition?

In each, the second part (or, in the last example, the first part) cannot stand alone: Že máš pravdu and Protože pršelo are fragments. They need the main clause to lean on. This dependence is exactly what makes them subordinate — and what triggers the comma.

Relative clauses with který

A relative clause is a special subordinate clause that describes a noun. It is introduced by který ("which / who / that"), which agrees in gender and number with the noun it describes and is always fenced off by commas.

Note that the relative clause kterou čtu sits inside the main sentence, with a comma on each side. The form kterou is feminine accusative (agreeing with kniha), while který is masculine nominative (agreeing with člověk). For the full pattern see relative clauses.

The comma rule in one breath

This is the practical payoff of the whole distinction:

Czech puts a comma before every subordinate clause, and before the contrastive coordinators (ale, však, a proto, a tak). It does NOT put a comma before plain additive a, i, or nebo.

The contrast is sharp: no comma before a (coordination, addition), but a mandatory comma before protože (subordination). This is governed entirely by the type of conjunction, not by how the sentence "feels."

The fuller set of comma rules, including the cases where even a takes a comma (for example a proto), lives on the subordinate-clauses-and-commas page.

Same idea, two structures

A useful exercise is to express one thought both ways. Take "It rained, so we stayed home":

The compound version chains two equal events; the complex version subordinates the reason. Both are perfectly natural — the choice is stylistic. Notice the comma appears in both, but for different reasons: a tak is a contrastive coordinator, and protože is a subordinator.

Why English habits mislead

English comma practice is looser and partly optional, and it does not map onto Czech. English often omits the comma before "because" ("We stayed home because it rained") and sometimes adds one before "and" in a list (the Oxford comma). Czech ignores both habits. Czech commas are grammatical, not stylistic: they mark clause boundaries by conjunction type. So the English instinct of "comma where I'd pause" will steer you wrong in both directions — you will drop the obligatory comma before protože and insert a stray one before a.

English drops the "that" and the comma ("I think you're right"); Czech keeps že and requires the comma before it. This is one of the most frequent slips for English speakers.

Common mistakes

Plain a joining two clauses in simple addition takes no comma.

Every subordinating conjunction, protože included, is preceded by a comma.

The content clause introduced by že is subordinate, so the comma is obligatory — even though English would drop both the comma and the word "that."

A relative clause with který needs a comma on both sides where it is embedded in the main clause.

Ale is a contrastive coordinator and always takes a comma before it.

Key takeaways

For deeper dives, see the coordinating conjunctions overview, the subordinating conjunctions overview, the a vs. i distinction, and simple sentence structure.