Accompaniment with S plus Instrumental

English uses one little word, with, for two very different ideas. "I'm going with my brother" means togetherness — my brother and I, side by side. "I cut it with a knife" means instrument — the knife is the tool. English happily uses with for both. Czech splits them apart, and the instrumental case (the 7. pád, the seventh case, answering kým? / čím? — "with whom? / with what?") sits at the center of both, distinguished by one small word: the preposition s (or its vocalized form se).

This page is about the first meaning — accompaniment, togetherness, "in the company of." For that, Czech uses s/se + the instrumental case. The contrast with the bare, prepositionless instrumental of means is the single most important thing to lock in, so it runs through everything below. Get it right and you will never say the Czech equivalent of "I'm cutting bread in the company of a knife."

S + instrumental = accompaniment

When two parties are together — you and a person, a drink and its addition, a conversation and its other side — use s plus the instrumental.

In each case the second party is genuinely alongside the first: the brother accompanies me, the milk joins the coffee, you are my conversation partner. This is the everyday "with" of social life, and it is everywhere in basic conversation — jdu s kamarády (I'm going with friends), bydlím s rodiči (I live with my parents), seznámil se s ní (he got to know her).

The crucial contrast: bare instrumental = means

Now the heart of the matter. The instrumental case has a second, equally common job: marking the tool or means by which an action is performed — and for that, there is no preposition at all. The bare instrumental is "by means of."

Here nožem (knife), perem (pen), and autem (car) carry no s. The bare ending alone says "by means of." This is covered in full on the instrumental of means, but the comparison belongs here because it is where learners go wrong.

The danger is real and slightly comic. If you add s to a tool, you change the meaning literally: nožem means "using a knife," but s nožem would mean "in the company of a knife" — as though the knife were your companion rather than your instrument.

When s becomes se

Like the preposition v/ve in the locative, s gets a vowel added — becoming se — when the following word starts with an awkward consonant cluster, so it is easier to pronounce. You will hear se before words beginning with s, z, š, ž and certain clusters.

The pronoun forms are worth memorizing as fixed phrases: se mnou (with me), s tebou (with you), s ním / s ní (with him / with her), s námi (with us), s sebou (with oneself — famously the Czech word for "to take away," as in kávu s sebou, "coffee to go").

The instrumental endings

The endings themselves are remarkably consistent across the language — many learners find the instrumental the most "regular" case. The hallmark sounds are -em for hard masculines and neuters, -ou for feminine -a nouns, and -mi / -y / -ami in the plural.

So s matkou pairs the accompaniment preposition with the -ou feminine ending; s dětmi uses the special plural dětmi.

Common Mistakes

Key Takeaways

• The instrumental is the
  7. pád
  , answering kým? / čím? — "with whom? / with what?"
• s/se + instrumental = accompaniment ("together with"): jdu s bratrem, káva s mlékem, mluvím s tebou.
• The bare instrumental, no preposition, = means ("by means of"): nožem, perem, autem. Adding s to a tool wrongly turns it into a companion.
• s → se before consonant clusters: se sestrou, se mnou, se psem. Note the set phrase s sebou ("to go / with oneself").
• Endings: -em (masc/neut), -ou (fem -a), plural -mi / -ami.

For the tool meaning in full, see the instrumental of means; for the other prepositions that govern this case (pod, nad, před, mezi, za), see prepositions that take the instrumental.