Learn Hardcore Finnish: Pöydällä on kynä ja kumi, koska olen kirjoittanut paperille. - There is a pen and an eraser on the table, because I have written on paper.

In existential sentences, Finnish almost always uses the 3rd person singular form of the verb, even if there is more than one thing:
- Pöydällä on kynä ja kumi. – On the table there is a pen and an eraser.
- Pöydällä on kirja ja kaksi vihkoa. – On the table there is a book and two notebooks.

If you said “Pöydällä ovat kynä ja kumi”, it sounds unusual or at least very marked; native speakers would normally change the word order instead (see next question).

To use ovat, you generally put the things at the beginning:

Kynä ja kumi ovat pöydällä. – The pen and the eraser are on the table.

So:

Pöydällä on kynä ja kumi. = “There is a pen and an eraser on the table” (existential, neutral way to introduce them).
Kynä ja kumi ovat pöydällä. = “The pen and the eraser are on the table” (they are already known items, now you state their location).

What is the difference between “Pöydällä on kynä ja kumi” and “Kynä ja kumi ovat pöydällä”?

They describe the same physical situation, but the focus and information flow are different:

Pöydällä on kynä ja kumi.
- Typical existential sentence.
- Focus starts with the location (pöydällä – on the table).
- You are introducing the existence of these objects at that location.
- Pragmatically: “On the table, there is a pen and an eraser.”
Kynä ja kumi ovat pöydällä.
- Normal subject–verb–adverbial order.
- Focus is on kynä ja kumi as known items.
- You are saying where they are, not that they exist there.
- Pragmatically: “The pen and the eraser are on the table.”

In English, both can often be translated similarly, but in Finnish the choice tells the listener whether you’re:

presenting new items at a location (Pöydällä on…), or
locating already-known items (Kynä ja kumi ovat…).

Why is it pöydäLLÄ and not pöydäSSÄ?

Both are locative cases but express different relationships:

pöydällä (adessive, -lla/-llä) = on the table, on the surface, at the table.
pöydässä (inessive, -ssa/-ssä) = in the table, inside the table.

In this sentence, the pen and eraser are on top of the table, so Finnish uses adessive:

Pöydällä on kynä ja kumi. – There is a pen and an eraser on the table.

Pöydässä on kynä would literally mean there is a pen inside the table (for example, inside a hollow table).

Why is it paperiLLE (paperille) and not paperiLLA (paperilla)?

The difference is:

paperille (allative, -lle) = onto the paper, movement toward the surface.
paperilla (adessive, -lla) = on the paper, staying on the surface.

In olen kirjoittanut paperille, the focus is on the action of writing onto the paper: the writing has been applied to the paper.

You could use:

Olen kirjoittanut paperille. – Emphasis on the act of writing onto the paper.
Teksti on paperilla. – The text is on the paper. Emphasis is on where the text now is.

So paperille suits the idea of “I have (just) written onto paper” better than paperilla, which would describe a static location.

Could we say “Olen kirjoittanut paperilla” instead of “paperille”?

You can say kirjoittaa paperilla, but it tends to mean:

using paper as the medium, in contrast to something else:
- Kirjoitin paperilla, en tietokoneella. – I wrote on paper, not on a computer.

In Olen kirjoittanut paperille, the emphasis is that the content has been written onto the paper (there is now writing on the sheet).

So:

Olen kirjoittanut paperilla. – More like “I have done my writing on paper (instead of digitally).”
Olen kirjoittanut paperille. – “I have written onto the paper (there is text on the paper now).”

For the typical “I wrote (something) on a sheet of paper”, paperille is the most natural.

Why paperille and not paperiin or paperissa?

These are different local cases:

paperille (allative) – onto the paper (to its surface).
paperiin (illative) – into the paper (into the interior).
paperissa (inessive) – in the paper (inside it).

Writing is conceptually happening on the surface of the paper, so Finnish sees this as movement onto the paper:

kirjoittaa paperille – write onto a sheet of paper.

Kirjoittaa paperiin would sound odd in normal contexts, as if you were somehow writing into the paper’s interior.

Why is the verb “on” singular even though there are two items (kynä ja kumi)?

Because of the existential sentence structure:

In sentences like Pöydällä on kynä ja kumi, the grammatical “subject” is not really in normal subject position.
The verb in these existential sentences is almost always 3rd person singular, regardless of whether there is 1 or 10 items.

Compare:

Pöydällä on kynä. – There is a pen on the table.
Pöydällä on kynä ja kumi. – There is a pen and an eraser on the table.
Pöydällä on monta kirjaa. – There are many books on the table.

To use ovat, you would usually switch to a normal subject–verb order:

Kynä ja kumi ovat pöydällä.

Why not partitive: why “kynä ja kumi” instead of “kynää ja kumia”?

In existential sentences, the choice between nominative and partitive for the “thing that exists” changes the meaning:

Nominative singular/plural (kynä ja kumi)
- Refers to whole, countable items, often more definite:
- Pöydällä on kynä ja kumi.
  → There is a (specific) pen and (a specific) eraser on the table.
Partitive singular (kynää, kumia)
- Indicates an indefinite amount, or “some” of something:
- Pöydällä on kynää ja kumia.
  → On the table there is some pen and some eraser – this would usually sound strange; it suggests matter/material, not objects.
- More natural with mass nouns:
  Pöydällä on vettä. – There is some water on the table.

So we use nominative here because we are talking about whole, separate objects: one pen and one eraser.

What does “kumi” mean here? I’ve seen it translated as “rubber” or “condom” too.

The word kumi has several meanings in Finnish, depending on context:

rubber (the material) – basic meaning.
eraser (for pencil) – in school/office contexts:
- kynä ja kumi in a school sentence usually means “a pen and an eraser”.
condom – in colloquial speech, especially in adult contexts.

In your sentence:

Pöydällä on kynä ja kumi, koska olen kirjoittanut paperille.

Given the context of writing on paper, kumi here is understood as a pencil eraser, not a condom.

How is “olen kirjoittanut” formed, and what tense is it?

Olen kirjoittanut is the present perfect in Finnish.

Structure:

olla (to be) in present tense + active past participle of the main verb.

For kirjoittaa (to write):

stem: kirjoitta-
active past participle: kirjoittanut

Then combine:

minä olen kirjoittanut – I have written
sinä olet kirjoittanut – you have written
hän on kirjoittanut – he/she has written
me olemme kirjoittaneet – we have written
te olette kirjoittaneet – you (pl.) have written
he ovat kirjoittaneet – they have written

In your sentence:

koska olen kirjoittanut paperille = “because I have written on the paper.”

It describes an action that has already happened and is relevant to the present situation (the pen and eraser are on the table as a result).

Why use “olen kirjoittanut” instead of simple past “kirjoitin”?

Both are possible, but the nuance is a bit different:

Olen kirjoittanut paperille.
- Present perfect.
- Focus on a past action with a connection to the present (result still matters now: the writing and thus the pen and eraser are relevant now).
Kirjoitin paperille.
- Simple past (preterite).
- Focus more on the finished action in the past, not necessarily on its present result.

In many everyday contexts, both could work, but:

Pöydällä on kynä ja kumi, koska olen kirjoittanut paperille.
Sounds very natural: “There is a pen and an eraser on the table because I have (just) been writing on the paper.”

Using kirjoitin might feel a bit more detached from the present situation.

Is the comma before “koska” necessary?

Yes. In standard written Finnish, you always put a comma before subordinating conjunctions like:

koska (because)
että (that)
jotta (so that)
jos (if)
kun (when, as)
etc.

So the correct punctuation is:

Pöydällä on kynä ja kumi, koska olen kirjoittanut paperille.

If you move the koska-clause to the front, you also use a comma:

Koska olen kirjoittanut paperille, pöydällä on kynä ja kumi.

Can the “koska” clause come first, and does the word order change?

Yes, you can put the reason first:

Koska olen kirjoittanut paperille, pöydällä on kynä ja kumi.

The word order inside the koska-clause stays normal:

Subordinate conjunction + subject + verb (+ complements)
koska
- olen
  - kirjoittanut paperille

You do not invert the word order like in some languages (e.g., German). Finnish keeps it straightforward:

Pöydällä on kynä ja kumi, koska olen kirjoittanut paperille.
Koska olen kirjoittanut paperille, pöydällä on kynä ja kumi.

Both are grammatically correct; the second one simply emphasizes the reason first.