Я сижу за столом.

I am sitting at the table.

Breakdown of Я сижу за столом.

• я: I
• сидеть: to sit
• стол: the table
• за: at

Questions & Answers about Я сижу за столом.

What case is столом, and why is that form used here?

Столом is the instrumental case of стол (table).

• Nominative: стол – the basic dictionary form
• Prepositional: (о) столе – used mostly with о, в, на for “about / in / on the table”
• Instrumental: столом – used with some prepositions (like за, под, над) and for “with/by means of”

In Я сижу за столом, the preposition за (“at / behind”) requires the instrumental case to express location (“I am located at the table”).
So: за + столом (instrumental) = at the table / behind the table.

Why is it за столом and not на столе?

За столом = at the table, usually implying you are sitting at it, using it (eating, working, etc.).

На столе = on the table, physically on top of the tabletop.

• Я сижу за столом. – I am sitting at the table (on a chair, the table is in front of me).
• Кот сидит на столе. – The cat is sitting on the table.

So for a person sitting at a table in a normal way, Russians say за столом, not на столе.

Why is it столом and not столе? I thought location often uses -е.

Russian uses different cases for location depending on the preposition:

• With в and на, static location usually takes the prepositional case:

  • в доме – in the house
  • на столе – on the table

• With за, под, над, между, static location normally takes the instrumental:

  • за столом – at/behind the table
  • под столом – under the table
  • над столом – above the table

So столе is the prepositional case and is correct after на (на столе), but after за for location we need instrumental, so за столом.

What is the infinitive of сижу, and how is this verb conjugated?

The infinitive is сидеть – “to sit, to be sitting”.

Present tense conjugation:

• я сижу – I sit / I am sitting
• ты сидишь – you sit / are sitting (singular, informal)
• он / она / оно сидит – he / she / it sits / is sitting
• мы сидим – we sit / are sitting
• вы сидите – you sit / are sitting (plural or formal)
• они сидят – they sit / are sitting

So Я сижу за столом literally is “I sit / I am sitting at the table.”

Where is the word “am” in Russian? Why isn’t it Я есть сижу за столом?

In Russian, the present tense of быть (“to be”) is normally omitted in simple statements:

• English: I am sitting at the table.
• Russian: Я сижу за столом.

The idea of “am” is already contained in the present tense verb сижу.
You would not say я есть сижу – that sounds wrong in modern Russian.

Present-tense есть (from быть) only appears in some special, mostly emphatic or archaic uses, not in normal sentences like this.

Can I leave out я and just say Сижу за столом?

Yes, you can say Сижу за столом.

Russian verb endings show person and number, so сижу already tells us the subject is “I”.

• Я сижу за столом. – neutral, full form.
• Сижу за столом. – also grammatical; sounds a bit more like a note, a reply, or a fragment in a conversation.

You include я when:

• you want to be clear or neutral,
• you want to contrast: Я сижу за столом, а он стоит у окна. – I’m sitting at the table, and he is standing by the window.

What is the difference between за столом and за стол?

The difference is case and meaning:

• за столом – instrumental, static location

  • Я сижу за столом. – I am (already) sitting at the table.

• за стол – accusative, movement to that position

  • Я сажусь за стол. – I am sitting down at the table.
  • Я сел за стол. – I sat down at the table.

Summary:

• за + instrumental = where something is (location)
• за + accusative = where something moves to (direction)

Does Я сижу за столом mean “I sit at the table” or “I am sitting at the table”?

It can mean both, depending on context. Russian has one present tense form for:

• habitual / repeated actions (“I sit there (regularly)”)
• an action happening now (“I am sitting there (right now)”)

Examples:

• Я каждый день сижу за этим столом. – I sit at this table every day.
• Что ты делаешь? – Я сижу за столом. – What are you doing? – I am sitting at the table.

English separates “I sit” vs “I am sitting”; Russian uses сижу for both. Context (adverbs, time expressions, the situation) tells you which is meant.

Can I say Я у стола instead of Я сижу за столом? What is the difference?

You can say Я у стола, but it does not mean the same thing:

• у стола = by/near the table, just close to it
  
  • Я стою у стола. – I am standing by the table.
• за столом = at the table in the usual sense – you are on a chair, using the table (eating, writing, working).

So:

• Я сижу за столом. – I am seated at the table (taking part in what’s happening there).
• Я у стола. – I am by the table (maybe standing, maybe not using it).

For the normal “I’m sitting at the table”, за столом is the natural choice.

How do I know that столом takes -ом and not some other ending in the instrumental case?

Стол is a masculine noun with a hard consonant ending (no vowel at the end). The usual instrumental singular ending for such nouns is -ом:

• стол → столом – table → by/at the table
• дом → домом – house → by/with the house
• нос → носом – nose → with the nose

Masculine (and neuter) nouns ending in a soft consonant or -й often take -ем instead:

• герой → героем – hero → by/with the hero
• конь → конём – horse → by/with the horse

So стол fits the regular pattern “hard masculine → -ом in instrumental”, giving столом.