The instrumental case (with / by means of)
The instrumental expresses the tool you use ('by means of') and accompaniment with the preposition 's/sa' ('together with'). Masculine and neuter nouns take -om (voz → vozom), feminine -a nouns take -om too (kafa → kafom). It also marks means of transport without a preposition.
Examples
- Putujem vozom. I travel by train.
- Pišem olovkom. I write with a pen.
- Idem sa sestrom. I'm going with my sister.
The full lesson
Everything in the video, in text.
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You travel by train, you write with a pen, you go with your sister. By what? With whom? In Serbian one case covers all of that — the instrumental. Master it and you instantly sound more natural. Let's nail it down completely.
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The instrumental has two main jobs. First, it marks the MEANS — the tool or way you do something, the "by means of what". Second, it marks COMPANY — the person you're with. It answers "by what?" („čime?“) and "with whom?" („s kim?“).
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Here are the endings. Masculine and neuter take „-om“: „voz“ becomes „vozom“, „auto“ becomes „autom“. Feminine in „-a“ also takes „-om“: „kafa“ becomes „kafom“, „olovka“ becomes „olovkom“. One ending for almost everything — that's the heart of the instrumental.
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Let's start with transport, because that's the biggest trap. How do you travel? „Vozom“ — and with no preposition at all. Putujem vozom. „I travel by train.“ „Voz“ takes „-om“ and becomes „vozom“. The ending alone carries the meaning "by train, by means of the train" — you don't need any preposition.
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Now the means — the tool you do something with. What do you write with? „Olovkom“. „Olovka“ drops „-a“ and takes „-om“: Pišem olovkom. „I write with a pen.“ Notice: in Serbian there's no word „s“ here — the ending „-om“ alone means "by means of the pen". An instrument goes in the bare instrumental.
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Now the instrumental's second job — company. When you're WITH someone, you use the preposition „s“ or „sa“ and put the person in the instrumental: Idem sa sestrom. „I'm going with my sister.“ „Sestra“ becomes „sestrom“, with „sa“ in front. Here the preposition IS required — because we're talking about company, not means.
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When „s“, when „sa“? Simple rule: use „sa“ before a word starting with „s“, „z“, „š“ or „ž“, so the sounds don't clash — hence „sa sestrom“, „sa Žarkom“. In all other cases plain „s“ is enough.
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Back to means, because the instrumental also covers the WAY you do something. What do you cut bread with? „Nožem“: Sečem hleb nožem. „I cut the bread with a knife.“ „Nož“ takes „-em“ instead of „-om“, because it ends in a soft consonant. But the meaning is the same — bare instrumental, a means with no preposition.
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Let's see the full forms so they stick. A hard stem takes „-om“: „voz“ becomes „vozom“, „kafa“ becomes „kafom“. A soft stem — one ending in „j“, „č“, „ž“, „š“ or „c“ — takes „-em“: „nož“ becomes „nožem“, „muž“ becomes „mužem“.
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Now the main trap — and the reason you're here. For transport and means you do NOT use a preposition. You say „idem vozom“, not „idem s vozom“. Keep the preposition „s“ only for company, for people. The train isn't your company — the train is your means.
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To make it clear, here's a contrast. „Putujem autobusom“ — that's a means, no preposition. But „razgovaram sa vozačem“ — that's company, a person, so it takes „sa“. Same case, but the preposition depends on whether it's means or company.
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And a last example, joining both senses in one sentence. Means with no preposition, company with a preposition: Putujem autobusom sa prijateljem. „I travel by bus with a friend.“ „Autobusom“ — means, bare instrumental; „sa prijateljem“ — company, with a preposition. Both in the instrumental, but only one takes „sa“.
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To recap. The instrumental answers "by what?" and "with whom?". The ending is „-om“, and „-em“ after soft consonants. Means and transport go with no preposition: „idem vozom“, „pišem olovkom“. Company takes the preposition „s“ or „sa“: „sa sestrom“. Remember: the train is a means, not company.