Finnish for busy people

The Partitive Case – Partitiivi – Finnish Grammar

This article deals with the partitive case, which answers the questions “mitä?” and “ketä?”. It’s a topic that will continue to be challenging for a very long time while you’re learning Finnish. My advice is to take it little by little and not try to learn it all at once.

Table of Contents
  1. The Use of the Partitive Case
    1. After numbers
    2. After words that express quantity
    3. With mass nouns
    4. With negative sentences
    5. With irresultative phrases
    6. With partitive verbs
    7. With prepositions
  2. The Formation of the Partitive Case
    1. The partitive of the personal pronouns
    2. Words ending in a single vowel
    3. Words ending in 2 vowels
      1. Words ending in two of the same vowel
      2. Words of one syllable ending in two vowels
      3. Adjectives ending in two different vowels
      4. Nouns ending in two different vowels
    4. Words ending in -i
      1. New words ending in -i
      2. Old words ending in -i
      3. Old words ending in -si
      4. Old words ending in –li, -ni, -ri
    5. Words ending in an –e
    6. Words ending in a consonant
      1. Words ending in -nen
      2. General rule for other words ending in a consonant
      3. Words ending in –us
      4. Non-Finnish words ending in a consonant
  3. Consonant Gradation in the Partitive Case
  4. The Partitive Case in Spoken Finnish

1. Use of the Partitive Case (mitä, ketä)

The partitive has no equivalent in English and many other languages. That makes it hard to understand what its function is. In some cases, the use of the partitive coincides with the plural form in other languages, but it’s not the same as the plural.

When a group of words all belong together (say: a pronoun, an adjective and a noun), all three of them will be put in the partitive.

  • “There are three [beautiful young women] in the room.” becomes “Huoneessa on kolme [kaunista nuorta naista].
  • “I buy ten [playful cats].” becomes “Ostan kymmenen [leikkisää kissaa].
  • “I have two [crying unhappy children].” becomes “Minulla on kaksi [itkevää surullista lasta].

1.1. After numbers

The partitive is used in connection with the numbers. Because of that, many new language learners assume the partitive is the plural form. This is not the case. There is a separate plural (the plural nominative) and in addition there is also a partitive plural.

You don’t use the partitive after the number “yksi”, but you do use it after the number “nolla”. Adjectives will be inflected in the same case as the noun they’re connected to.

Yksi Finnish English
yksi kuppi kaksi kuppia two cups
yksi olut kolme olutta three beers
yksi talo nolla taloa zero houses
yksi vaate viisi vaatetta five pieces of clothing (pic)
yksi kaunis nainen neljä kaunista naista four beautiful women
yksi komea poika viisi komeaa poikaa five handsome boys

1.2. After words that express a quantity

We use the partitive case with words that express a quantity, an amount. For example, the words kuppi, kulho and lasi are things which contain an amount of something. Units of measurement (litra, kilo, metri, gramma) also express an amount. These words are very much like numbers in that sense.

You can find more words that express quantity here.

Finnish English
monta banaania many bananas
kuppi kahvia a cup of coffee
kulho mysliä a bowl of muesli
pullo viiniä a bottle of wine
tölkki olutta a can of beer
metri köyt a meter of rope
litra maitoa a liter of milk

1.3. With mass nouns

When you’re dealing with an indefinite amount of something, you will use the partitive case. This is especially common with mass nouns (ainesana). For example, the word maito (milk) is a mass noun because we can’t count it in units. We can’t say “one milk, two milks”. Instead, you say yksi litra maitoa (one liter of milk) or yksi kulho maitoa (a bowl of milk).

You will use the partitive case with mass nouns in “minulla on” -sentences (#1), object sentences (#2). By using the partitive case, you express that you’re dealing with an indefinite, unspecified amount of the mass noun. You don’t know how much it is exactly; just some amount.

You can often recognise mass nouns when translating them to English. First, these nouns generally don’t get an article (“I buy milk” rather than “I buy a milk”). In addition, most of the time, the English translation could include the word “some”.

In complement sentences (#3) you will have an article (e.g. “Maito on kylmää” means “The milk is cold”). You can read more about complement sentences in this article. In addition, you can also take a look at how Duolingo introduces this type of sentences in this article.

# Basic form Finnish English
1 kahvi Minulla on kahvia. I have coffee. / I have some coffee.
1 juusto Onko meillä vielä juustoa? Do we still have cheese?
1 ruoka Teillä on ruokaa. You have food. / You have some food.
2 maito Minä juon maitoa. I drink milk. / I am drinking some milk.
2 riisi Keitän riisiä. I cook rice. / I am cooking rice.
2 ketsuppi Ostamme ketsuppia. We buy ketchup. We are buying ketchup.
3 mehu Mehu on oranssia. The juice is orange.
3 liha Tämä liha on outoa. This meat is strange.
3 kana Tämä kana on outoa. This chicken is strange. (chicken as a food, not the animal)

1.4. With negative sentences

In almost all sentence types, you will have the partitive in a negative sentence. Exception: complement sentences (predikatiivilause).

Finnish English
En osta tä puseroa. I won’t buy this sweater.
En avannut ikkunaa. I didn’t open the window.
Minulla ei ole autoa. I don’t have a car.
Täällä ei ole uima-allasta. There’s no swimming pool here.

1.5. With irresultative phrases

Irresultative means the action is incomplete (versus resultative, which is complete). When an activity is currently taking place, you will put the object in the partitive. The result of the action hasn’t been achieved yet. The partitive might also be meant like in part 1.3., where you plan to read some of the book, but not all of it. You can find similar examples here.

Finnish English
Luen kirjaa. I’m reading some of the book.
Luen kirjaa. I’m currently reading the book.
Luen kirjan. I’m going to read the whole book.

1.6. With partitive verbs

Some verbs always require the object to appear in the partitive case. These are called “partitive verbs“. You will need to learn these by heart, because English doesn’t have anything comparable.

Verb Finnish English
rakastaa Minä rakastan sinua. I love you.
odottaa Sinä odotat bussia. You wait for the bus.
pelata Hän pelaa tennis. She plays tennis.
ajaa Minä ajan autoa. I’m driving a car.
opiskella Te opiskelette suomea. You’re studying Finnish.
auttaa Me autamme hän. We help her.

1.7. With prepositions

Prepositions are fairly uncommon in Finnish, but they do exist. Read more about them on my Finnish prepositions page.

Preposition Finnish English
ennen Tulin kotiin [ennen sinua]. I came home [before you].
ilman Tulin kotiin [ilman takkia]. I came home [without a coat].
keskellä Talo on [keskellä metsää]. The house is [in the middle of the forest].

2. The Formation of the Partitive Case

The ending of the partitive can be -a, -ta or -tta, depending on what kind of word they are attached to. In order to correctly choose between -a and , you will need to first learn about vowel harmony.

2.1. The partitive of the personal pronouns

The partitive of personal pronouns goes as follows:

PP Partitive Finnish English
minä minua Minua ärsyttää. I feel annoyed.
sinä sinua En rakasta sinua. I don’t love you.
hän hän Odotan hän asemalla. I wait for her at the station.
me mei Etkö nähnyt mei? Didn’t you see us?
te tei Tei väsyttää. You (plural) feel tired.
he hei Älä kuuntele hei. Don’t listen to them.
kuka ke Ke sinä rakastat? Who do you love?

2.2. Words ending in a single vowel (-a/-ä, -u/-y, -o/-ö): add -a/-ä

Basic form Partitive Basic form Partitive
kala kalaa tyyny tyynyä
talo taloa seinä seinää
loma lomaa hylly hyllyä
melu melua sänky sänkyä
helppo helppoa homma hommaa

2.3. Words ending in 2 vowels

2.3.1. Words ending in two of the same vowel: add -ta/-tä

Basic form Partitive Basic form Partitive
sampoo sampoota filee filee
elokuu elokuuta vapaa vapaata
essee essee toffee toffeeta

2.3.2. Words of one syllable ending in two vowels: add -ta/-tä

This rule covers words with both two of the same vowel and two different vowels, as long as the word is one syllable.

Basic form Partitive Basic form Partitive
maa maata tie tie
syy syy t työ
puu puuta

2.3.3. Adjectives ending in two different vowels

Adjectives fairly regularly end in -ea/eä. In these cases, we can use both the ending -a/-ä and -ta/-tä. The single -a is much more common in current Finnish, so I would suggest using that form. In spoken language, you will hear vaikeeta, tärkeetä and nopeeta, with a long vowel sound.

Basic form Partitive
vaikea vaikeaa / vaikeata
pim pimeää / pimeä
nopea nopeaa / nopeata
tärk tärkeää / tärkeä
haalea haaleaa / haaleata

2.3.4. Nouns ending in two different vowels

Nouns ending in -ia will get one -a/-ä added to their end in the partitive case. Nouns with other vowel combinations will get -ta/-tä

Basic form Partitive Basic form Partitive
allergia allergiaa valtio valtiota
arabia arabiaa kallio kalliota
italia italiaa radio radiota
asia asiaa video videota
fobia fobiaa selfie selfie

2.4. Words ending in –i

Find out more about the inflection of different types of words ending in -i!

2.4.1. New words ending in -i: add -a/-ä

New words are often loanwords. Usually they’re recognisable because they resemble words in other languages, like pankki for “bank”, or paperi for “paper”. Loanwords are easier than Finnish words because they don’t undergo as many changes when you add endings.

Basic form Partitive Basic form Partitive
banaani banaania paperi paperia
kahvi kahvia pankki pankkia
posti postia maali maalia
tili tiliä adverbi adverbia

2.4.2. Old words ending in -i: replace -i with -ea/-eä

Old words are very often nature words. After all, nature has been around for so long that Finns have had names for them since the very beginning. Some words’ age can be confusing, for example äiti “mother” is actually a new Finnish word, even though mothers have been around since the beginning of time!

Basic form Partitive Basic form Partitive
suomi suomea ovi ovea
järvi järveä kivi kiveä
sormi sormea nimi nimeä
lahti lahtea lehti lehteä

I have a more extensive list of words that belong to this type here.

2.4.3. Old words ending in -si: replace -si with -tta/-ttä

More old words, but this time with -si at their end. It’s also important that this rule is only for old words, which means new words like kurssi (kurssia) and marssi (marssia) are excluded from this rule.

Basic form Partitive Basic form Partitive
uusi uutta vuosi vuotta
si ttä kuukausi kuukautta
vesi vettä reisi reittä

I have a more extensive list of words that belong to this type here.

2.4.4. Old words ending in -li, -ni or -ri: replace -i with -ta/-tä

This rule is not 100 % foolproof. There are words that end in -hi, like lohi for example, that become lohta in the partitive. It’s also important that this rule is only for old words, which means words like lääkäri (lääkäriä), jonglööri (jonglööria) and konduktööri (konduktööria) are excluded from this rule. Exceptional: lapsi > lasta; lumi > lunta.

Basic form Partitive Basic form Partitive
pieni pien meri merta
sieni sien suuri suurta
nuori nuorta hiiri hiir
kieli kiel tuli tulta

I have a more extensive list of words that belong to this type here.

2.5. Words ending in -e: add -tta/-ttä

Basic form Partitive Basic form Partitive
huone huonetta perhe perhettä
kappale kappaletta kirje kirjettä
lentokone lentokonetta taide taidetta
parveke parveketta koe koetta

There are some words that end in -e that are exempt to this rule. These include names (Ville → Villeä), and some other words (kolme → kolmea, itse → itseä, nukke → nukkea).

2.6. Words ending in a consonant

2.6.1. Words ending in -nen: replace the -nen with -sta/-stä

Words ending in -nen are a very common wordtype in Finnish. For the partitive case, you will remove the –nen from the basic form and replace it with -sta/stä.

Basic form Partitive Basic form Partitive
nainen naista hevonen hevosta
suomalainen suomalaista eteinen eteistä
iloinen iloista ihminen ihmistä
sininen sinistä toinen toista

2.6.2. General rule for other words ending in a consonant

Most words ending in a consonant will get -ta/tä in the partitive case. This is true for most word types ending in a consonant. If you’re a beginner, you don’t need to look any further into these word types for now, it’s best to learn their inflection in more detail once you master the easier word types.

Basic form Partitive Basic form Partitive
mies mies hius hiusta
askel askelta rikas rikasta
keskus keskusta lyhyt lyhyt

The general rule applies to words of the following wordtypes:

2.6.3. Words ending in -us/ys

Normally, words ending in -Us just fall under rule 2.6.2 and get -tA added to their basic form. However, there are some words ending in -Us that will behave differently. You can read more about the difference here.

Basic form Partitive Basic form Partitive
rakkaus rakkautta tarjous tarjousta
ystävyys ystävyyttä opetus opetusta
pimeys pimeyttä kysymys kysymys
mahdollisuus mahdollisuutta vastaus vastausta

Some guidelines for finding the right conjugation:

  • If the word is based on a verb (such as opettaa > opetus), it will generally follow rule 2.6.2 instead (add –ta to the basic form of the word).
  • If the word is based on an adjective (such as pimeä > pimeys), it will get –tta in the partitive.
  • If the word is based on a noun (such as ystävä > ystävyys), it will get –tta in the partitive.
  • If the word ends in –uus/yys (double vowel), you will get –tta.

2.6.4. Non-Finnish words ending in a consonant

Loanwords and foreign names (e.g. Jonathan, Facebook) which end in a consonant will have an extra -i- added before the partitive’s -a/ä.

Basic form Partitive Basic form Partitive
Jonathan Jonathania Facebook Facebookia
William Williamia Windows Windowsia
Marian Mariania Steam Steamia
Mohamed Mohamedia McDonalds McDonaldsia

You might also want to check out these two articles:


3. Consonant Gradation in the Partitive Case

The partitive is complicated in many ways, but when it comes to consonant gradation it’s simple: the partitive form of each word will have the same consonants as the basic form. For wordtype A that means always strong, and for wordtype B always weak!

Wordtype A
Basic form Partitive Basic form Partitive
tyttö tyttöä pankki pankkia
puku pukua pöytä pöytää
hattu hattua kauppa kauppaa
silta siltaa kampa kampaa
hiekka hiekkaa apu apua

I have a separate article on wordtype A.

Wordtype B
Basic form Partitive Basic form Partitive
puhallin puhallinta tavoite tavoitetta
soitin soitinta savuke savuketta
keitin keitin opas opasta
rakas rakasta hammas hammasta
allas allasta allas allasta

I have a separate article on wordtype B.


4. The Partitive Case in Spoken Finnish

In spoken Finnish, the partitive ending –a can assimilate. This is only the case for certain vowel combinations: -oa, -öä, -ua, -yä, -ia, -iä, -ea, -eä. The partitive’s -a will be replaced by another of the word’s final vowel.

Written Spoken Written Spoken
tyynyä tyynyy taloa taloo
kahvia kahvii tuolia tuolii
suomea suomee järveä järvee

Adjectives such as vaikea end in a diphthong (see section 2.3.3). There words’ partitive is also special in spoken Finnish. That’s because the basic form will already be different in spoken language: vaikea will be vaikee in spoken language. This is only the case for adjectives ending in -ea/eä.

When we want to make vaikee partitive, we are dealing with a word that ends in a long vowel (see section 2.3.1). Thus, we use the –ta ending for these words. In fact, even if written Finnish, we can say vaikeata, but it’s much less common than vaikeaa.

Written Spoken Written Spoken
vaikeaa vaikeeta pimä pimee
nopeaa nopeeta kauheaa kauheeta

 

That concludes the article on the partitive case!

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This was the best online source for learning Finnish. Now it looks “modernized”, energetic and motivating. Thank you for all your efforts. All the best…

Thank you! 🙂

AyeBoushaba

This is by far the easiest Finnish grammar explanation I have encountered. Thank you for explaining everything in its most simple form. God bless you and keep doing what you do.

Michael Hämäläinen

Below are a few other partitive uses I’ve found in my notes and reading of other pages on this site:

[Comparisons – in place of kuin (than)]

cf. 2.2. Comparative: using the partitive case

[Cause or reason: old idiomatic use]

I don’t have much knowledge of this, but Korpela writes:

In old idiomatic use, the partitive may express cause or reason, especially when it is a state of mind or trait in a personality, e.g. Hän teki sen ilkeyttään (He did it out of malice) [note: ilkeyttä is partitive of ilkeys; –än is 3rd-person possessive suffix]. This applies to verbs describing actions. In such contexts, the word may have an attribute, e.g. pelkkää ilkeyttään (out of mere malice). It is also possible to use the elative, without a possessive suffix, e.g. pelkästä ilkeydestä.

[Use with prepositions and postpositions]

cf. Finnish Prepositions – Finnish Grammar

[Archaic locational case]

The original locational use (corresponding to “from”) of the partitive is reflected in some adverb-like words like alempaa (from below, from a lower position) and for comparatives of nouns, e.g. rannempaa (from closer to the shore).
cf. my comment on Adverbs of Location: Täällä, Kaikkialla, Ylhäällä

Shanna

Any advice for -ki words? Lokki and harkki become lokkia and harkkia, but hanki and hauki become hankea and haukea, and I don’t believe any of those are considered loan words. Is it because of the double k that they are different?

Inge (admin)

I didn’t know the answer, but you’re definitely onto something with your guess! I went through Kielitoimiston sanakirja to hunt down enough words to be able to compare.

Here’s the result: All words ending in -kki become -kkia except for kaikki! Words ending in -ki don’t always reveal right away whether they become -kia or -kea.

Old words with -ki
arki : arkea
hanki : hankea
hauki : haukea
henki : henkeä
hetki : hetkeä
hiki : hikeä
joki : jokea
jälki : jälkeä

New words in -ki
aski : askia
koti : kotia
kuski : kuskia
laki : lakia
hoki : hokia
huki : hukia
kaki : kakia
konki : konkia

Obvious -kki loanwords
blokki : blokkia “block”
breikki : breikkiä “break”
bulkki : bulkkia “bulk”
drinkki : drinkkiä “drink”
feikki : feikkiä “fake”

Surprising new words
These three are words that refer to old things, but are nevertheless new. They support that the rule for -kki words is to always have -kkia for the partitive.
liekki : liekkiä “flame”
lokki : lokkia
mökki : mökkiä

The only old word ending in -kki
kaikki : kaikkea

Thanks for the interesting question!

Michael Hämäläinen

Hi Shanna and Inge,

I also tried investigating myself by filtering the KOTUS word list, as described here. Short answer is that there are 499 entries belonging to KOTUS type risti, 45 entries of KOTUS type ovi, plus a handful of rare foreign-derived exceptions (example).

The example words lokki and harkki are KOTUS type risti words, which follow the rule in 2.6.1. New words ending in –i: add –a/-ä. Also included are words with –kki suffix (Wiktionary entry and listing), which include some verb-derived nouns like lemmikki (“pet” from <lempiä (to love) +‎ –kki ) (VISK) and slang/colloquial terms like karkki (candy) (VISK), as well as most foreign loanwords (as mentioned in the article).

The example words henki and hauki are KOTUS type ovi words, which follow the rule in 2.6.2. Old words ending in –i: replace –i with –ea/-. The 45 entries are all 2-syllable old Finnish words ending in –Vki or –V{l/n/r/s/t}-ki, as well as kaikki.

So, a pragmatic approach might be to learn to recognise the ovi-type words and apply the risti rule in all other cases.

Hope that helps!

cine

Kaikkea is singular, kaikkia is plural.

monika

I am a bit confused. Do we change k-p-t in partitiivi?

I came across this sentence ‘HUOM!! – partitiivissa ei k-p-t vaihtelua´
Thank you in advance!!

Last edited 3 years ago by monika
Inge (admin)

That’s correct! No consonant gradation in the partitive: words look like their basic form. You can see it in section 3: both wordtype A words (pöytä > pöytää) and wordtype B words (puhallin > puhallinta) always look like their basic form. It’s just that the basic form of these two types is different: strong stays strong, weak stays weak.

Sebghatullah Noori

Kiitoksia näistä tiedosta🙏

Kalevo

moi! I have a question why dont use the plural partitive in the case of ”Ostan kymmenen kissaa”? Why not ”Ostan kymmenen kissoja”? I feel like we are buying a part of the cats, not the whole cats. Im wrong, I know, but why? Thank you!

Inge (admin)

The partitive has a lot of other functions besides expressing “part of something”. Take “Minä rakastan sinua” for example. This doesn’t mean I love only part of you. Time to let go of that overgeneralization concerning the partitive case!

I wish I had some kind of an explanation though. In Finnish you never use the plural after numbers. We use the singular partitive. This is just the rule for all numbers except for one. But why? “That’s just the way it is” :p

Kalevo

Kiitos paljon vastauksesta, Inge!

olen poika

this website is the best ! i love it ♥️

Krishna Sharma

Lasissa on mehua =There’s juice in the glass.
Is it correct if I want to say The juice is in the glass ( mehu on lasissa). No partitivi for mehu, because the object (mehu) is in the starting of the sentence. Can you shed some lights on this.

You’re correct! The type of sentence will influence the case needed. The subject of a sentence is normally in the basic form.

Mehu on lasissa. > Base sentence
Mehu on kylmää. > Complement sentence
Lasissa on mehua. > Existential sentence
Juon mehua. > Object sentence

Yassine boukrim

I feel like you should’ve started with the formation of the partitiivi case first. But thank you it was very helpful

Manolis Gustafsson

Hello! Lovely page! You say that ”Some verbs always require the object to appear in the partitive case”, could you please give an example of such a verb? Are these more uncommon compared to partitive verbs?

Verbs that require the object to appear in the partitive case are partitive verbs, that’s what that section is all about 🙂

Manolis

Oh sorry, I meant to write the opposite. Could you please give an example of a verb that doesn’t require the object to appear in the partitive case? And are these less common compared to partitive verbs? Thanks 🙂

Inge (admin)

Finnish has a lot of partitive verbs but also a lot of total object verbs. Total object verbs (which in a regular sentence get the genitive case) include, for example, myydä, ostaa, avata, sulkea, antaa, ottaa, haluta, löytää and varastaa.

Read more about partitive objects and total objects here.

Manolis

Perfect! Thank you so much, this answers my question fully 🙂

Manolis

However, can’t you say eg. ”Minä myyn autoa” (I’m selling a car; unspecified)? While in ”minä myyn auton” it’s a specific car that you’re talking about? But if myydä is a total object verb, then that would mean only the latter is correct…

Inge (admin)

“Minä myyn auton” can mean “I sell a car” or “I sell the car”.Partitive doesn’t work there. It’s still one specific car, even if you’re not specifying who owns it.

Krishna Sharma

Luen Kirjoja. does this sentence only says that I am reading some(unspecified) books or does it also shed some light on the completion or incompletion of the action

If your phrase is this short, it’s just an unspecified plural amount of books, without making clear if I’m currently reading them, reading part or intending to finish them.

Krishna Sharma

löytyykö tätä suomesta. why it is tätä and not tämä. Is löytää a partitive verb. I can’t find any partitive rule that can explain this. Thanks in advance

It’s the funny “negative answer is implied” question type. Similar to how a cashier might ask you “(Haluatko) kuittia?” However, in your sentence, the tätä is not the object of your sentence, it’s the subject (the verb löytyä doesn’t get an object). The answer is most likely implied: Tätä ei löydy Suomesta.

krishna sharma

i still did not get it. can you elaborate more, why it is tätä,and not tämä

Last edited 1 year ago by krishna sharma

When a cashier asks you: “do you want the receipt”, they’re expecting you to say “no”, so they use the partitive case – the negativity is in their mind already. Similarly, here, the thing probably CAN’T be found in Finland.

Then again, maybe in your context, they are just talking about a drink or a food? You didn’t give any context. In that case it’s just a normal uncountable noun: “Can drink/food X be found in Finland?” We’re not talking about a specific bottle of the stuff, just the stuff in general.

Emmanuelle

In the example “I have two crying unhappy children”, instead of lasta (sing.), shouldn’t it be lapsia (pl.)? Thanks a lot! This is the best finnish grammar EVER!!!!!!

Inge (admin)

In Finnish, you use the singular partitive (lasta) rather than the plural partitive (lapsia) when there’s a number included. So we get “Minulla on kaksi itkevää surullista lasta” (with the number) but “Minulla on itkeviä surullisia lapsia (without the number).

Emmanuelle

Oh, I get it now! Thanks for clarifying it!

Esinath Munyai

This is so useful and informative. Thank you for making it easy to understand.

Ewelina

woah that amazing how i understood it so fast i will definitely come back!!!

Yousif
Inge (admin)

That looks amazing,Yousif!

Esinath

Thanks Yousef…its really amazing and understandable.kiitos veljeni 🙏

Maks

“ia” its not a diphthong

Inge (admin)

True! Thank you 🙂

Marcin

I think “ea” is not a diphthong either (as in vaikea).

It seems that some vowel combinations can be diphthongs, others never are. However, sometimes even the same vowel combination is a diphthong in most of the words it appears but not in all. For instance “au” is a diphthong in “sauna” but not in “rakkaus”. Are there some rules for that? In the case of “rakkaus” it seems to be due to the suffix “-us” but maybe there are some other instances when a particular vowel combination is not a diphthong even though it usually is in other words?

Jukka_K

Those -ea and -eä endings can vary in different dialects and spoken forms, so they can sometimes be diphthongs or long vowels, sometimes in different syllabes.
Let’s check variants of vaikea and its partitive case. I mark syllable boundaries with ”-”
Vai-ke-a : vai-ke-aa
Vai-ki-a : vai-ki-aa
Vai-kea : vai-kea-ta
Vai-kee : vai-kee-ta
About the same phonetic ”mechanics” works in the other end-of-the-word vowel combinations.