“It’s Fun to” Sentences - "On hauskaa" Lausetyyppi

This article deals with the sentence type (lausetyyppi) commonly referred to as “on hauskaa -lause” (“it’s fun to” sentence). This term is especially common in sources for Finnish as a second language learners.

In addition to “fun”, we can extend this sentence type to “it’s scary to”, “it’s easy to” or “it’s not smart to”.

Finnish	English
On mielenkiintoista opiskella suomea.	It is interesting to study Finnish.
Ei ole järkevää nukkua tunnilla.	It isn’t smart to sleep in class.
On hassua uida vaatteet päällä.	It is weird to swim with clothes on.
Oli pelottavaa lentää Suomeen.	It was frightening to fly to Finland.
On tylsää odottaa lentokentällä.	It is boring to wait in the airport
Ei ole vaarallista kävellä metsässä.	It isn’t dangerous to walk in the forest.

Table of Contents

Prototypical features of “on hauskaa” sentences
ON: The verb olla in the third person singular
KIVA: The adjective – On vaikea(a) olla nainen
1. Nominative vs. partitive
2. Partitive preferred in certain wordtypes
3. Basic form preferred in certain wordtypes
IHME: Using a noun rather than an adjective – On ihme, että…
OPISKELLA: The infinitive of the verb – On kiva opiskella suomea.
ETTÄ: Subordinate clauses – On kiva, että…
KIRJASTOSSA: A location – Kirjastossa on kiva opiskella suomea.
KESÄLLÄ: A time – Kesällä on kiva opiskella suomea.
SUOMEA: An object – Kieliä on kiva opiskella.
MINUSTA: An opinion – Minusta on vaikea oppia suomea.
MINUN: An experiencer – Minun on vaikea oppia suomea.
1. “I find it hard”
2. “It’s hard for me” vs. “I think it’s hard”
3. Possible confusion with necessity sentences
Without the verb olla – Ihanaa että tulitte.
“Se” on hauskaa.
Complement sentences: Elämä on hauska.

Terminology

This sentence type generally is glossed over pretty quickly in more sources. Here’s some information about how it’s generally mentioned in grammar sources.

VISK doesn’t specify “on hauskaa” sentences as their own sentence type. Rather, they are addressed under the more general term tilalause, which also contains sentences such as “On tiistai” and “On tuulista“. I’m planning to write another article discussing those sentence types at some point in the future.
Fred Karlsson doesn’t list this as a sentence type of its own. He identifies the verb in this sentence type as a “postposed infinitive” (which he doesn’t explain any further). He seems to consider “On hauskaa” -sentences as a type of complement sentences, listing a couple of examples in the section that covers sentences such as “Maito on valkoista“.
Leila White uses the term “On hauskaa” -lauseet. She explains the topic fairly well.
Suomen mestari 3 uses the term “On hauskaa…” and gives one example.
An older textbook for highschool called “Suomen kielen ja kulttuurin lähde” lists this sentence type as an “on hyvä lause“, with three examples.

1. Prototypical features of “On hauskaa” sentences

Never “se”!
In Finnish, “It is hard to study” will just be “On vaikea opiskella“.
The verb olla in the third person singular
The verb can be any tense or mood (e.g. on, oli, on ollut, ei ole ollut, olisi).
An adjective describing the sensation
The adjective can be in the nominative case or the partitive case.
A verb in the basic form
The verb of the sentence will be in its infinitive form (e.g. opiskella, mennä, syödä).

2. ON: The verb olla in the third person singular

This sentence type typically starts with the verb olla. The verb can be any tense or mood, positive or negative (e.g. on, oli, on ollut, ei ole ollut, olisi).

Note that these sentences don’t have a subject like in English! In Finnish, “It is fun” will just be “On hauskaa”. In English, we call the “it” of these sentences a “dummy subject”: a pronoun that has no meaning by itself but fills the position of a normal subject. Finnish has no need for this type of subject.

Making the sentence negative will not influence the case the adjective appears in. For example, “Ulkona on kiva istua” will become “Ulkona ei ole kiva istua”, with kiva in its basic form regardless of the negative sentence. This makes this sentence type different from an existential sentence (Ulkona on pöytä. vs. Ulkona ei ole pöytää).

Finnish	English
On hyvä olla lomalla.	It is good to be on vacation.
Oli hyvä olla lomalla.	It was good to be on vacation.
On ollut hyvä olla lomalla.	It has been good to be on vacation.
Ei ollut hyvä olla lomalla.	It wasn’t good to be on vacation.
Olisi hyvä olla lomalla.	It would be good to be on vacation.
Olisiko ollut hyvä olla lomalla?	Would it have been good to be on vacation?
Eikö ollut hyvä olla lomalla?	Wasn’t it good to be on vacation?

3. KIVA: The adjective – On vaikea(a) olla nainen

3.1. Nominative vs. partitive

One issue with this sentence type is that the adjective can be in the nominative case (e.g. on ihana) or the partitive case (e.g. on ihanaa). Many of the most common adjectives will be used in the basic form (e.g. on hyvä), while many other adjectives will have the partitive case ending. For some adjectives, both the nominative and the partitive are possible.

As a second language learner, it can be tricky to know whether you should use the basic form or the partitive case. If you’re feeling overwhelmed, you could just default toward using the partitive form. It’s mentioned in multiple sources that it’s hard to perceive a difference in meaning between the nominative and the partitive case. Some adjectives just are preferably used in one case more than the other.

3.2. Partitive preferred in certain wordtypes

Some adjectives will nearly always appear with the partitive case ending. This is the case for adjectives ending in -inen (#1), -tOn (#2) and -kAs (#3) as well as participle adjectives (#4).

#	Finnish	English
1	On mielenkiintoista oppia lausetyyppejä.	It is interesting to learn sentence types.
1	Oli surullista kuulla miehen ongelmista.	It was sad to hear about the man’s problems.
1	Onko vaarallista asua Suomessa?	Is it dangerous to live in Finland?
1	On fantastista työskennellä asiantuntijana.	It is fantastic to work as an expert.
2	On sopimatonta valehdella tästä asiasta.	It is inappropriate to lie about this matter.
2	On varomatonta vähätellä tätä.	It is imprudent to downplay this.
3	Olisi ollut älykästä liittyä heti.	It would have been smart to join right away.
3	On tehokasta valmistaa suuria määriä.	It is efficient to produce large quantities.
4	Onko pelottavaa puhua mielenterveydestä?	Is it scary to talk about mental health?
4	On stressaavaa matkustaa vauvan kanssa.	It is stressful to travel with a baby.
4	On rentouttavaa saunoa illallisen jälkeen.	It is relaxing to have a sauna after dinner.
4	On lohduttavaa kuulla, etten ole ainoa.	It is comforting to hear that I’m not the only one.

3.3. Basic form preferred in certain wordtypes

Certain very common basic adjectives will usually appear in this sentence type in their nominative form. This includes the adjectives hyvä, paha, kiva, turha, varma, mukava, hankala, ihana, helppo, vaikea, parempi, helpompi, vaikeampi, paras, sama and – surprisingly enough – hauska. Note the bolded word “usually”.

Finnish	English
Olisi kiva tietää, mitä heille kuuluu.	It would be nice to know what’s up with them.
Olisi kiva olla lentokapteeni.	It would be nice to be a flight captain.
On turha teeskennellä, että…	It is pointless to pretend that…
On turha toivoa, että tämä muutos pysähtyisi.	It is futile to hope that this change would stop.
On mukava liikkua metsässä.	It is nice to walk in the forest.
On ollut hankala päästä mukaan.	It has been difficult to get involved.
Oli ihana tulla kotiin.	It was wonderful to come home.
On hyvä, että päätös oli yksimielinen.	It is good that the decision was unanimous.
Oli hyvä huomata, että en ollut ainoa.	It was good to notice that I wasn’t the only one.
On helppo tulla toimeen Arin kanssa.	It is easy to get along with Ari
Ei ole helppo olla optimisti.	It is not easy to be an optimist.
Oli vaikea hengittää.	It was hard to breathe.
On ollut vaikea päästä eteenpäin.	It has been hard to go further.
Olisi ollut parempi elää vuonna 1925.	It would have been better to live in 1925.
On parempi, että tyttöni asuu isänsä luona.	It is better for my daughter to live with her father.
On helpompi soittaa kuin olla soittamatta.	It is easier to call than not to call.
On vaikeampi huomata hitaampaa muutosta.	It is harder to notice slower change.
On paras olla sanomatta mitään.	It is best not to say anything.
Oli paha, että tulimme tänne.	It was bad that we came here.
On paha kasvattaa lasta siinä tilanteessa.	It is bad to raise a child in that situation.
On turha toivoa korvausta.	It is pointless to hope for compensation.
On aivan sama, paranenko tästä vai enkö.	It doesn’t matter if I get better from this or not.
On sama mennä autolla kuin bussilla.	It is the same going by car as by bus.

Three notes here:

Note that – while there is a general tendency for these words to be used in their basic form – this isn’t a strict rule. For example, both the partitive and the basic form are about equally common in Google search results for this phrase: “Ei ole helppo(a) päättää.” As a second language learner, you might just learn these specific words by heart and use them in their basic form.
The name of this sentence is confusing. It’s much more common to say “on hauska” than “on hauskaa“. Somewhere in the past, someone decided the name of this sentence type should have partitive and this has been passed along to newer course books without a second thought. I am doing the same in this article because this is the name you will find elsewhere. Perhaps “on vaarallista” would be a better name, as in “On vaarallista kopioida termejä sokeasti“.
In his Master’s thesis, Pasi Salmela remarks on one tendency for the use of the partitive vs. the nominative. He states that if the partitive form of the adjective ends in an -a/ä, but the basic form does not, the partitive is “almost always” correct. There are holes in his theory but it’s interesting. It would explain why some shorter adjectives such as kiltti and hullu are more commonly used in the partitive (On kilttiä mennä, on hullua mennä).

My personal approach to the nominitive/partitive minefield is to remember the few words that are (almost) exclusively used in the nominative case, and use the partitive case with every other adjective.

4. IHME: Using a noun rather than an adjective – On ihme, että…

Several sources I’ve looked into mention that this sentence type includes phrases which have a noun rather than an adjective. However, the only two examples of this I could find are “on onni” and “on ihme“. I’ve come up with some other ones on my own, but it’s hard to be sure if these examples actually fit this sentence type when all I have to compare them to are two examples.

Finnish	English
Oli onni, ettei tulipalo sattunut yöaikaan.	It was lucky that the fire didn’t happen at night.
Ei ollut ihme, että Ari palkittiin.	It was no wonder that Ari was rewarded.
On sääli, että Ari ei voinut tulla.	It is a shame that Ari couldn’t come.
On virhe kuvitella, että olemme kaikki samanlaisia.	It is a mistake to imagine we’re all the same.
On ilo nähdä teidät jälleen täällä.	It is a pleasure to see you (plural) here again.
On ollut kunnia palvella Suomea.	It has been an honor to serve Finland.

5. OPISKELLA: The infinitive of the verb – On kiva opiskella suomea.

The main verb in this sentence type will be added in its basic form (ie. its infinitive).

Finnish	English
On mielenkiintoista opiskella suomea.	It is interesting to study Finnish.
On vaikeaa muistaa uusia sanoja.	It is difficult to remember new words.
Onko pelottavaa puhua suomalaisten kanssa?	Is it scary to talk with Finns?

6. ETTÄ/KUN/MIKSI: Adding a subordinate clause – On kiva, että…

While the prototypical “on hauskaa” sentence is used in combination with a verb in its infinitive form (#1), we can also use a subordinate clause (sivulause). This clause most often starts with että (#2), but with some adjectives a question word such as miksi or miten (#3) or a question such as onko (#4) also work.

#	Finnish	English
1	On surullista lukea uutisia kuolonkolareista.	It is sad to read news about fatal crashes.
2	On surullista, että ihmiset joutuvat pelkäämään.	It is sad that people have to be afraid.
3	On epävarmaa, kutsutaanko minut juhliin.	It is uncertain whether I’ll be invited to the party.
4	On surullista, miten yleistä ongelma on.	It is sad how common the problem is.
2	Onko varma, että Ari on syyllinen?	Is it certain that Ari is the culprit?
2	On ymmärrettävää, että kaikki ovat järkyttyneitä.	It is understandable that everyone is shocked.
2	On epäreilua, että taakka on kokonaan meillä.	It is unfair that the burden is entirely on us.
2	On vain luonnollista, että parisuhde muuttuu.	It is only natural that a relationship changes.
2	Oli selvää, että Ari tiesi vastauksen.	It was clear that Ari knew the answer.
2	On todennäköistä, että elämme simulaatiossa.	It is likely that we are living in a simulation.
3	Ei ole tärkeää, tuleeko voitto vai tappio.	It doesn’t matter whether I/you/we win or lose.
3	On epäselvää, meneekö lakiuudistus läpi.	It is unclear whether the legislative reform will pass.
3	Oli epävarmaa, palaisiko Ari enää koskaan.	It was uncertain whether Ari would ever return.
4	On epävarmaa, kuka ottaa vastuun.	It is uncertain who will take responsibility.
4	On hämmentävää, kuinka moni nainen ei tiedä tätä.	It is confusing how many women don’t know this.
4	On hämmästyttävää, miten suuri vaikutus tällä on.	It is amazing how much of an impact this has.
4	On surullista, kuinka huonosti tämä hoidetaan.	It is sad how poorly this is handled.
4	Ei ole tärkeää, milloin aloitat.	It is not important when you start.

7. KIRJASTOSSA: Adding a location – Kirjastossa on kiva opiskella suomea.

This sentence type – at its core – only consists of OLLA + ADJECTIVE + VERB INFINITIVE. However, you can easily add an element in one of the location cases at the start of these sentences.

Finnish	English
[Suvilahdessa] on hauska skeitata.	It is fun to skate [in Suvilahti].
[Junalla] on hauska matkustaa minne tahansa.	It is fun to travel anywhere [by train].
[Siihen] oli hyvä lopettaa.	It was good to end it [there].
[Asiasta] olisi turha hermoilla.	It would be useless to worry [about it].
[Arille] on turha yrittää selittää mitään.	It is useless to try to explain anything [to Ari].
[Kotoa] oli turha odottaa tukea ja ymmärrystä.	It was pointless to expect support [from home].
[Maaseudun maisemissa] on mukava lenkkeillä.	It is nice to go jogging [in the rural landscape].
[Terassilta] oli hankala löytää pöytää.	It was difficult to find a table [on the terrace].
[Tähän] on vaarallista pysähtyä.	It is dangerous to stop [here].

If you’re really interested in grammar, you might wonder if these sentences won’t be considered existential sentences if they start with a location, followed by the verb in the third person singular. There is a big difference though. Existential sentences tell us that there’s a thing/person/concept in a certain place (e.g. Sivulahdessa on skeittihalli). “On hauskaa” sentences explain how we feel about doing an action in a certain place (e.g. Suvilahdessa on hauska skeitata).

Another sentence type that might come to mind would be simply “Suvilahdessa on hauskaa“. Personally, I would place this with another sentence type: the ambient clause (tilalause). The term tilalause is a catch-all used by sources such as Iso suomen kielioppi, which includes some other sentences types as well such as “On tiistai” and “Sataa“. I will try to get my article about ambient clauses published soon.

8. KESÄLLÄ: Adding a time – Kesällä on kiva opiskella suomea.

Another element that’s easy to add to the beginning of these sentences is an expression of time such as kesällä (in summer). These can also be added to the end of the sentence. Word order in Finnish often follows this rule: Old/known information at the beginning – New/unknown information at the end of the sentence. Thus, if the new information in these sentences is the time frame, we will put it at the end of the sentence. If another element is the new information, the time frame will be at the beginning.

Finnish	English
[Iltaisin] oli vaikea saada unta.	[In the evenings] it was hard to sleep.
[Kesällä] on mukava uida ja syödä mansikoita.	In summer it is nice to swim and eat strawberries.
[Jouluna] on hauska pukeutua hienosti.	[At Christmas] it is fun to dress up nicely.
[Silloin] on mukava hiihtää.	It is nice to ski [then].
[1960-luvulla] oli tärkeää näyttää tärkeältä.	[In the 1960s] it was important to look important.

9. SUOMEA: Adding an object – Kieliä on kiva opiskella.

While this sentence type usually starts with olla + adjective, Finnish is quite flexible with word order. We can place the object of the sentence at the start. As I mentioned in section 8, word order is often used to express which part of the information of a sentence is new, and which part is already known from the context. Take the sentence “Tätä kirjaa oli hauskaa lukea” (It was fun to read this book) for example. Here, you should imagine that we have already established which book we are talking about. This is not the important information, so we put it at the front of the sentence. Of course, the sentence “Oli hauska lukea kirjaa” is also a perfectly fine sentence.

Finnish	English
[Tilastoja] on hauska tarkastella.	It is fun to look [at the statistics].
[Nuorten juttuja] on hauska kuunnella.	It is fun to listen [to young people’s stories].
[Kirjaa] oli hauska lukea.	It was fun to read [the book].
[Läksyt] on mukava tehdä yhdessä.	It is nice to do [homework] together.
[Lastenhoito] olisi ollut hankala järjestää.	It would have been difficult to arrange [childcare].
[Ystäviä ja perhettä] oli aina ihana nähdä.	It was always wonderful to see [friends and family].
[Tottumuksesta] on vaikea luopua.	It is hard to break [a habit].
[Yhteyttä] ei ole vaikea nähdä.	It is not hard to see [the connection].

10. MINUSTA: Adding an opinion – Minusta on vaikea oppia suomea.

At the beginning of the sentence, we can add whose opinion to the statement is. This can be done using all the regular elements Finnish uses to express opinions, such as minusta and minun mielestäni.

Finnish	English
[Minusta] on vaikea ymmärtää tätä.	[I think] it is difficult to understand this.
[Mielestäni] on kiva pukeutua hassusti.	[I think] it is nice to dress funny.
[Minusta] tähän olisi hyvä lopettaa.	[I think] it would be worth stopping here.
[Minusta] on hauska asua lähellä järveä	[I find] it fun to live near a lake.
[Arista] on hauska katsoa ruohon kasvamista.	[Ari finds] it fun to watch grass grow.
[Matista] on kiinnostavaa tehdä töitä kiinalaisten kanssa.	[Matti finds] it interesting to work with the Chinese.

11. MINUN: Adding an experiencer – Minun on vaikea oppia suomea.

11.1. “I find it hard”

You can add an element that expresses who’s experiencing the emotions about the action. This “experiencer” will be at the start of the sentence in the genitive case. In English, you will use “for” when directly translating (e.g. It is hard for me to learn Finnish). A more relaxed translation could contain the verb “to find” (e.g. I find it difficult to learn Finnish).

Not all adjectives allow for an experiencer to be added. For example “on kiva(a)” and “on mahtava(a)” just don’t work if you add “minun”.

Finnish	English
[Minun] on vaikea ymmärtää tätä.	It is difficult [for me] to understand this.
[Minun] oli vaikea oppia suomea.	It was difficult [for me] to learn Finnish.
[Opettajien] oli hyvä työskennellä siellä.	It was good [for the teachers] to work there.
[Heidän] oli turha yrittää hämätä meitä.	It was useless [for them] to try to fool us.
[Maahanmuuttajien] on ollut hankala sopeutua.	It has been difficult [for immigrants] to adapt.
[Teidän] on helppo istua täällä ja sanoa noin.	It is easy [for you (pl.)] to sit here and say that.
[Minun] on vaikea pysyä perässä.	[I found] it difficult to keep up.

11.2. It’s hard for me vs. I think it’s hard

Note the contrast between the previous section and this one. When using the -sta form (elative case), we’re giving our opinion on the topic, while the -n form (genitive case) describes the personal feeling of the experiencer.

Take this example: “On vaikea ymmärtää tätä” (it’s hard to understand this). When you say “Minun on vaikea ymmärtää tätä“, you express that you have trouble understanding it personally. It translates as “It’s hard for me to understand this”. In contrast, saying “Minusta on vaikea ymmärtää tätä“, you’re expressing that understanding it is difficult in general, rather that speaking of your personal struggle with it. We can replace minusta with mielestäni in these sentences.

Minun (kokija)	Minusta (mielipide)
[Minun] oli vaikea oppia suomea. “I found it hard to learn Finnish.”	[Minusta] oli vaikea oppia suomea. “I think learning Finnish is hard.”
[Meidän] on helppo vastata kysymykseen. “It was easy [for us] to answer the question.	[Meistä] on helppo vastata kysymykseen. “[In our opinion] it’s easy to answer the question.

11.3. Possible confusion with necessity sentences

A genitive subject can turn these sentences into necessity sentences. This is especially the case for the following adjectives: hyvä, paha, paras(ta), välttämätöntä, tarpeellista, aiheellista, and suositeltavaa.

For example, “Sinun olisi hyvä syödä enemmän vihanneksia.” (It would be good for you to eat more vegetables) is a suggestion or recommendation, which makes it a necessity sentence. It doesn’t express an experience like an “on hauskaa” sentence would. One important factor for this is the tense used. For example, “Sinun olisi hyvä asua täällä” expresses that it would be good for you to live here (which could be a suggestion or recommendation). “Sinun on ollut hyvä asua täällä.” addresses what the experience has been living here. This has no hint of a suggestion.

Necessity sentence	“On hauskaa” sentence
[Meidän] on parempi jatkaa matkaamme. “We had better continue our journey.”	[Meidän] on parempi asua täällä kuin Oulussa. “It’s better [for us] to live here than in Oulu.”
[Minun] olisi hyvä syödä enemmän marjoja. “I should eat more berries.”	[Minun] oli hyvä tavata isoisäsi. “It was good [for me] to meet your grandfather.”

I would say this is an unimportant detail. These sentences differ only in meaning, not in the way they are built. Thus, it feels really unimportant to me to specify what sentence type these are.

12. Without the olla-verb – Ihanaa että tulitte!

With some adjectives, you can leave out the verb olla and create a sentence that’s an exclamation. This only works with certain adjectives. You can’t, for example, say “Vaikea on oppia suomea“. It seems to be limited to certain adjectives that are followed by an että-sentence. I wouldn’t get too creative with this unless you have a lot of experience with Finnish, since there isn’t a clear rule which adjectives it works with.

Finnish	English
Ihanaa, että tulitte!	(It is) great that you came!
Harmi, ettet tullut mukaan!	(It is) too bad you didn’t come!
Hyvä, että asia etenee.	(It is) good that things are progressing.
Kiva, että tulit.	(It is) nice that you came.
Hauska kuulla, että voitit!	(It is) nice to hear that you won!
Hauska tutustua sinuun!	(It is) nice to meet you!

13. “Se” on hauskaa

We can of course form the sentence “Se on hauskaa“. That’s just a complement sentence, where se refers to whatever we were talking about before: “Kaikkien pitäisi lukea enemmän, koska se on hauskaa.” (Everybody should read more because it is fun). We can also say “Se on hauska video” (It’s a fun video), which is another complement sentence. However, this article doesn’t deal with complement sentences.

Rather, we’ve been specifically talking about “on hauskaa” sentences. Rule number one for “on hauskaa” sentences is that you do not use “se” like you do in English. For example, the English sentence “It is important to understand this” will be translated as “On tärkeää ymmärtää tätä“, without “it” (which is called a “dummy pronoun” or tukipronomini in Finnish).

Such a nice rule, which makes it unfortunate that in certain situations you can add “se” to “on hauskaa” sentences. I very dearly love rules, so let’s have a look at the rules for this exception:

It only works for “On hauskaa” sentences with an että-lause (sometimes also an indirect question),
It will require a change in word order, with the adjective before the olla-verb, and
The adjective must strongly express that the statement is unusual, surprising, or very important. We can also use the superlative form.
Don’t use se with adjectives that express that something is clear, certain, natural, possible or understandable.

Finnish	English
Ainutlaatuista on se, että musikaali järjestetään kirkossa.	What is unique is that the musical is held in a church.
Keskeistä on se, että tekeminen on yhteistä.	What is key is that the work is done together.
Keskeistä on se, miten saamme ihmiset innostumaan.	What is vital is how we get people excited.
Tärkeää on se, että asiakas saa hyvää palvelua.	What is important is that the customer receives good service.
Ratkaisevaa oli se, että Ari oli tietoinen kavalluksesta.	What was crucial was that Ari was aware of the embezzlement.
Hämmentävää on se, että heitä on niin paljon.	What’s confusing is that there are so many of them.
Tärkeintä oli se, että meitä kuunneltiin.	What was most important was that we were listened to.
Yllättävintä on se, että lumelääkkeet todella toimivat	What is most surprising is that placebos really work.

This isn’t a rule set in stone either. The conclusion at the end of the article in Kielikello states: “It’s probably not sensible to write clear rules about when the word “se” should be used and when it should be avoided – the writer should boldly trust his or her own linguistic sense here.”

14. Complement sentence: Elämä on hauskaa.

There is one sentence type that is reminiscent of “on hauskaa” sentences but different in some ways. Just like an “on hauskaa” sentence, a complement sentence also consists of the verb olla in the third person singular combined with an (partitive/nominative case) adjective. However, there will be a subject to these sentences, and they will be lacking a verb. You can read more about this other sentence type here: Predikatiivilause – Complement sentence.

Predikatiivilause	“On hauskaa” lause
Elämä on mielenkiintoista. “Life is interesting.”	On mielenkiintoista olla elossa. “It’s interesting to be alive.”
Saunominen on rentouttavaa. “Having a sauna is relaxing.”	On rentouttavaa käydä saunassa. “It’s relaxing to have a sauna.”
Siivoaminen on tärkeää. “Cleaning is important.”	On tärkeää siivota. “It’s important to clean.”
Tämä on surullista. “This is sad.”	On surullista menettää ystäviä. “It’s sad to lose friends.