Woods wrote:However, what happens if the adjective is a predicate?
How would you say e.g. “Are you (pl.) ready?” – “Oletteko valmis?” No need to modify the adjective?
Predicate adjectives agree with the headword, too. If you say "oletteko valmis", you are using the polite form to address one person. The true plural forms are:Oletteko valmiita?
In this case, the first one is more common but you can use either of them without changing the meaning. With other nouns, the nominative one is usually understood as "a certain group of [headword]":Talot ovat kauniit
= The(se) houses are beautifulTalot ovat kauniita
= Houses (in general) are beautiful / The houses are beautiful
Nominative is also used with words that don't have a singular form:Housut ovat tiukat
= The(se) trousers are tight
But if you're speaking of many trousers, you can also say:Housut ovat tiukkoja
= All trousers are tight
(The latter one might be a bit weird on its own, but it works in certain contexts. For example, kaikki ostamani housut ovat tiukkoja
= all the trousers I bought/buy are tight)
Remember that the colours are adjectives, too:Housut ovat mustat
= The trousers are black
(Again, partitive works if you specify the group you're referring to: kaikki omistamani housut ovat mustia
= all the trousers I own are black)
The singular predicates
are usually in nominative if the headword is concrete:Minä olen hyvä tässä
= I'm good at thisPöytä on puhdas
= The table is clean
And in partitive if the headword is uncountable:Ruoka on hyvää
= The food is goodOstoksilla käyminen on hauskaa
= Shopping is fun
Sometimes both nominative and partitive are possible, but the meaning can change:Jäätelö on herkullinen
= Ice cream (cone) is deliciousJäätelö on herkullista
= Ice cream (mass noun) is deliciousIlma on kylmä
= The weather is coldIlma on kylmää
= The air is cold (eg. the air coming from an AC)Nuoriso on tyytyväinen
orNuoriso on tyytyväistä
= The youth are happy/satisfied (no change in meaning!)
I also found this:
3. Adjektiivinen predikatiivi on partitiivissa, jos sen ilmaisema ominaisuus omistetaan subjektin tarkoitteen jokaiselle osalle. Subjekti on tällöin abstrakti-, aine- tai ryhmäsana tai monikollinen.
4. Adjektiivinen predikatiivi on partitiivissa tavallisesti myös, jos subjektina on infinitiivi tai sivulause tai ellei lauseessa ole lainkaan subjektia. Kielen tavallisimmat adjektiivit voivat kuitenkin tällaisissa tapauksissa olla nominatiivissa.
3. The predicate adjective is in partitive if the feature/attribute is seen as belonging to every part of the subject.* In this case, the subject refers to an abstract concept or matter (love, shopping, food) or to a group (the youth), or it is in plural.
4. The predicate adjective is usually in partitive also if the subject is an infinitive or a subordinate clause or if there is no subject in the sentence. However, the most common adjectives can be in nominative.
* Basically, the idea is that "everything in shopping is fun" and "every piece of food is good", or "every person who is young is happy" and "every house is beautiful" -> therefore, ostoksilla käyminen on hauskaa, ruoka on hyvää, nuoriso on tyytyväistä, talot ovat kauniita
. But as you can see, languages rarely follow one set of rules with no exceptions.(FYI: In my dialect - possibly also in other dialects and/or spoken language - singular predicate adjectives that describe some emotions can be in partitive. I could say, for example, soli niin tyytyväästä = s/he was so satisfied/happy [with something], or moon rehevää = I'm proud [of something]. This is not possible in standard Finnish.)