Learn Hardcore Finnish: Tämä aine karkottaa hyttysiä ulkona. - This substance repels mosquitoes outside.

Tämä – this
- Demonstrative pronoun in nominative singular; here it works like a determiner: this substance.
aine – substance / material / chemical
- Noun, nominative singular. Together Tämä aine is the subject: this substance.
karkottaa – repels / drives away
- 3rd person singular present tense of the verb karkottaa (to repel, to drive away).
- It agrees with the subject Tämä aine.
hyttysiä – mosquitoes (in an indefinite, “some mosquitoes / mosquitoes in general” sense)
- Noun hyttynen (mosquito), in the partitive plural. It is the object of the verb.
ulkona – outside, outdoors
- An adverb of place. It tells you where the mosquitoes are being repelled.

So the structure is:

[Subject] Tämä aine – [Verb] karkottaa – [Object] hyttysiä – [Adverbial] ulkona.

Why is there no word for a or the in Tämä aine or some before hyttysiä?

Finnish simply does not have articles like English a / an or the, nor a separate word like some that’s required before plural or mass nouns.

Instead, definiteness and indefiniteness are expressed by:

Context
Word order
Case forms
Demonstratives such as tämä, se, tuo

In Tämä aine, the demonstrative tämä already does the job that this and partly this particular do in English. You don’t need (and cannot add) anything like an article.

For hyttysiä, the partitive plural already suggests some mosquitoes / mosquitoes (in general) rather than a specific, clearly delimited set of mosquitoes. So:

Tämä aine karkottaa hyttysiä ulkona.
→ This substance repels mosquitoes outdoors. (no article words needed in Finnish)

Why is it hyttysiä and not hyttyset? What does the partitive plural express here?

Hyttysiä is the partitive plural of hyttynen (mosquito). The choice of partitive vs. nominative (or genitive) object changes the meaning.

hyttyset (nominative plural): a specific, total set of mosquitoes
- Tämä aine karkottaa hyttyset.
  → This substance drives away the mosquitoes (all of them in the relevant group).
hyttysiä (partitive plural): an indefinite quantity, or mosquitoes in general
- Tämä aine karkottaa hyttysiä.
  → This substance repels mosquitoes (some / in general).

In this sentence, we are describing a general property of the substance (what it does in general), not a one‑time event affecting a known, complete group of mosquitoes. Finnish typically uses the partitive plural for that kind of generic or indefinite object:

Karhut syövät marjoja. – Bears eat berries.
Tämä aine karkottaa hyttysiä. – This substance repels mosquitoes.

So hyttysiä is chosen because:

The mosquitoes are not a specific, clearly limited set.
The sentence describes an ongoing or general ability, not a completed action on all mosquitoes.

What is the base form of hyttysiä, and how do we get from hyttynen to hyttysiä?

The dictionary (nominative singular) form is:

hyttynen – mosquito

Key forms:

Nominative singular: hyttynen
Partitive singular: hyttystä
Nominative plural: hyttyset
Partitive plural: hyttysiä ← the form in the sentence

Pattern:

Nouns ending in ‑nen often drop ‑nen and add ‑se‑ or ‑si‑ in many case and plural forms.
- ihminen → ihmisiä (people)
- kansalainen → kansalaisia (citizens)
- hyttynen → hyttysiä (mosquitoes)
For hyttynen, the plural stem becomes hyttysi‑.
The partitive plural ending is ‑ä (here, front vowel harmony), so:
- hyttysi‑ + ä → hyttysiä

So hyttysiä literally is mosquito‑(plural stem) + partitive‑plural ending.

What exactly is ulkona, and how is it different from ulos and ulkoa?

Ulkona is an adverb meaning outside / outdoors, describing a static location: being outside.

There is a trio you can learn together:

ulkona – outside, outdoors (being outside)
- Olen ulkona. – I am outside.
ulos – (to the) outside, out (movement to the outside)
- Menen ulos. – I go out / I’m going outside.
ulkoa – from outside (movement or origin from the outside)
- Tulen ulkoa. – I come from outside.

In Tämä aine karkottaa hyttysiä ulkona, ulkona says where the repelling happens: outdoors (not indoors). It doesn’t need a preposition like in or at; Finnish uses these adverb forms or case endings instead of prepositions.

Could the word order be different, like Ulkona tämä aine karkottaa hyttysiä?

Yes, Finnish word order is fairly flexible. The neutral, most common word order here is:

Tämä aine karkottaa hyttysiä ulkona.

You can change the order to highlight different parts of the sentence:

Ulkona tämä aine karkottaa hyttysiä.
- Emphasis on ulkona: Outdoors, this substance repels mosquitoes.
- You might say this if you are contrasting outdoors with indoors.
Tämä aine ulkona karkottaa hyttysiä.
- Possible but sounds less neutral; the placement of ulkona in the middle is less typical for this kind of simple statement.

Key points:

The finite verb (karkottaa) usually stays in 2nd position or fairly early in the clause in neutral sentences.
New or contrastive information often comes near the end or is moved to the front.

In everyday use, Tämä aine karkottaa hyttysiä ulkona is the standard, unmarked version.

Why does karkottaa look like the dictionary form? Where is the personal ending?

The dictionary form (1st infinitive) of the verb is karkottaa.
The 3rd person singular present form is also karkottaa for this verb type, so they look identical.

Conjugation in the present tense:

minä karkotan – I repel
sinä karkotat – you repel
hän karkottaa – he/she/it repels
me karkotamme – we repel
te karkotatte – you (pl) repel
he karkottavat – they repel

The personal ending for 3rd person singular is effectively ‑(A) here, and with this verb stem it merges so that the form looks the same as the infinitive.

So in Tämä aine karkottaa hyttysiä, karkottaa is not an infinitive; it is 3rd person singular present, agreeing with Tämä aine. Context and sentence structure tell you it’s a finite verb, not an infinitive.

What does aine mean here exactly? Is it medicine, a chemical, or just “thing”?

Aine is a fairly general word meaning substance, material, stuff, chemical. It can refer to:

A chemical substance (kemikaali, aine)
An ingredient (aine, ainesosa)
A physical material (materiaali, aine)

In this sentence, Tämä aine could be:

A chemical solution
A spray
A lotion
Any kind of active substance that repels mosquitoes

If you wanted to emphasize the product rather than the substance itself, you might hear:

Tämä tuote karkottaa hyttysiä. – This product repels mosquitoes.
Tämä hyttyskarkote karkottaa hyttysiä. – This mosquito repellent (product) repels mosquitoes.

So aine focuses on the substance / active material, not on it being a commercial product.

Why is tämä used and not se or tuo? What are the differences?

Finnish has three common demonstratives:

tämä – this (near the speaker)
tuo – that (over there) (farther away, often visible)
se – that / it (previously known or not in the immediate physical focus)

Rough guidelines:

tämä aine – this substance (physically close to me, the speaker, or currently being pointed at / held)
tuo aine – that substance (over there) (visible, but at some distance from the speaker)
se aine – that substance / it (already mentioned in the conversation, or not specifically pointed at)

In Tämä aine karkottaa hyttysiä ulkona, tämä suggests the speaker is presenting or holding the product, or otherwise treating it as something immediately present and being introduced: this (one right here).

In everyday speech, se is often used more than tämä, but in clear, neutral standard language, tämä aine is a natural way to say this substance.