Finnish has singular and plural for nouns much like in English. The nominative plural has the ending t, whereas in most inflected forms the plural suffix is i between the base word and the case suffixes. For example, the nominative plural of talo (house) is talot, whereas the inessive plural is taloissa (in houses), where ssa is the inessive case suffix. The details of the formation of plural are discussed in section Plural of nouns.
Adjectives have plural, too, and an attribute of a noun follows both the case and the number of noun. Thus, we say punainen talo (red house) but punaiset talot (red houses).
Finnish does not always use plural and singular the same way as English. One difference is that in Finnish, singular is used with numerals, e.g. “five houses” is viisi taloa.
We also say Panin saappaat jalkaan (I put boots on), using jalkaan (literally “into foot”) in singular. The same applies to other paired parts of the body in many phrases, e.g. pistää silmään (to stick out, literally “to stick to eye”). In such usage, the singular word has a collective meaning, referring e.g. to both feet or to both eyes. This is also reflected in words like silmäpuoli (one-eyed, literally “eye-half”).
Singular is also used in some phrases like taivas on pilvessä (the sky is clouded over) and mennä marjaan (to go berry picking; literally “to go into berry”), olla kalassa etc. They are discussed from a different perspective (use of cases) in sections Covering and Specialized uses of locational cases.
There are also other idiomatic uses of singular forms especially in poetic style, e.g. Siellä miestä kylmeni (a book title, referring to men “becoming cold”, i.e. dying).
English uses plural for the object in statements like “They shook their heads”, but in Finnish we say He ravistivat päätään, where päätään is a singular form of pää (head), with partitive suffix tä and possessive suffix än. We can say that in Finnish we use the singular because each person has only one head. Consistent with this, we say He heiluttivat käsiään when we mean that people waved both hands and He heiluttivat kättään when each person used just one hand; in English, both are are expressed “They waved their hands”.
When two attributes are connected with ja (and) or an equivalent conjunction, the noun they relate to is in singular in the old usage of Finnish. We say e.g. iso ja pieni koira (a small and a large dog) in singular, even though we are referring to two dogs. This extends to genitive attributes, too, e.g. suomen ja ruotsin kieli (the Finnish and Swedish languages), though it has become common and accepted to use plural here: suomen ja ruotsin kielet. Sometimes plural is even needed for clarity, to distinguish e.g. Annan ja Liisan koirat (Anna’s and Liisa’s dogs) from Annan ja Liisan koira (Anna’s and Liisa’s dog, i.e. a dog owned by them jointly).
The predicative is in plural when the subject is in plural. Thus, in the statement Nämä kukat ovat kauniita (These flowers are beautiful), both the predicate ovat and the predicative kauniita are in plural, since the subject nämä kukat is plural.
A predicative adverbial is often singular even when the subject and the predicate are plural. For example in Opettajat ovat usein sairaana (The teachers are often sick) the predicative adverbial sairaana is singular. The plural sairaina is also used, but singular is more common and fully accepted. The following principles apply to predicative adverbials:
Both in Finnish and in English, some nouns are used only in plural, even when the meaning is singular, such as farkut (jeans), housut (pants), sakset (scissors), silmälasit (glasses), and sortsit or shortsit (shorts). In linguistics, such words are called plural-only words or “plurale tantum” words. Finnish has some more of them, such as aivot (brain), kasvot (face), kottikärryt (wheelbarrow), lastenvaunut (pram), rintaliivit (bra), tikapuut (ladder), urut (pipe organ), and viikset (mustache) as well as many words denoting gatherings or festivities, e.g. avajaiset (opening ceremony), hautajaiset (funeral), häät (wedding), and ristiäiset (christening party). A difference in the opposite direction is that English uses “hair” to denote both a strand of hair and the totality of such strands in one’s head, whereas Finnish uses the word hius in singular for a strand of hair and the plural hiukset for a totality, synonymous with the (singular) word tukka.
Some words are used as plural-only in specialized meanings but otherwise normally. For example, kutsu (invitation) is used normally in singular and in plural, but in the meaning “party (for invited people)”, it is used only in plural: kutsut. Similarly, we have syntymäpäivä (birthday) as a normal word but syntymäpäivät (birthday party) in plural only.
However, a singular form can be used when the word appears as the first part of a compound word, such as hääkakku (wedding cake), housuntasku (pants pocket), and urkusoolo (organ solo). When the first part is in the genitive, a plural form is used in some words, e.g. urkujenpolkija (organ blower).
The word kiikari (binoculars, field glasses) can be used in singular, but it is often treated as a plural-only word, kiikarit, and this is now accepted.
Some name of countries and other entities are plural in form, e.g. Yhdysvallat (the United States) and Alankomaat (the Netherlands). There are also some Finnish place names used that way, e.g. Virrat. With them, the predicate and the predicative are usually singular, e.g. Virrat hyväksyi sopimuksen (Virrat accepted the contract). However, if the subject is plural in form only and denotes a singular concept, the predicative is in singular, e.g. Alankomaat on EU:n perustajajäsen (The Netherlands is a founding member of the EU). An adjective attribute is best avoided, since both kaunis Virrat and kauniit Virrat kuulostaisi oudolta; to circumvent this, one could say kaunis Virtain kaupunki.
A plural name may sometimes be used to denote either a single entity or a collection. For example, we normally say Kanariansaaret on… (The Canary Islands is…), but the plural ovat is also possible, if we think of it as referring to the different islands.
Some Finnish place names that end with nen have pecular inflection: all other forms but the nominative are plural. Examples: Kauniainen : Kauniaisten (of Kauniainen): Kauniaisissa (in Kauniainen), Ikaalinen : Ikaalisissa, Sörnäinen : Sörnäisissä. The inflection Kaustinen : Kaustisilla is also used, but the standard and more common inflection is in singular, Kaustisella.
Words that are use in plural in standard language are sometimes used in singular in speech and in informal writing, e.g. mun aivo (my brain). This is widely regarded as substandard.
The word markkinat (market; fair) has traditionally been used in plural only, e.g. Suomen markkinat (the Finnish market). However, in economic contexts it is increasingly used in singular, e.g. Suomen markkina, though this is still regarded as incorrect or colloquial by language authorities.
Plurale tantum words are often avoided by using synonyms that have normal inflection, e.g. the colloquial Kanaria for Kanariansaaret, the slang form Sörkka for Sörnäinen etc.
Words such as veljekset : veljesten are sometimes described as plurale tantum words, but they actually have plural meaning: veljekset refers to two or more person who are each other’s brothers. Note than in an expression like Villen veljet (Ville’s brothers) the simpler word veli : veljen is used. Instead, we say e.g. He ovat veljeksiä (They are brothers [of each other]).
The singular veljes : veljeksen is also possible, though normally only in the partitive in conjunction with a noun, e.g. seitsemän veljestä (seven brothers).
There are few words in this category, all with a suffix including -kset : -sten in plural, e.g. siskokset (sisters), sisarukset (siblings), serkukset (cousins), kaverukset (pals), ystävykset (friends), naapurukset (neighbours), kumppanukset (companions). The word sisarukset refers to both brothers and sisters, despite being derived from sisar (sister). The rare word sisarekset refers to sisters only, i.e. it is synonymous with siskokset
Plural forms are sometimes used for emphasis or style in singular meaning, especially in word pairs like maat ja mannut (house and home) and kreikat ja latinat (the Greek and Latin languages). In some greetings and wishes, the use of plural may give a more polite or more informal impression, e.g. hyvät jatkot (literally: good continuations) instead of hyvää jatkoa; they both mean “all the best”.
Many adverbials are plural forms of noun stems, even though they denote a state or mood, e.g. olla valveilla (to be awake) and olla nukuksissa (to be sleepy). This is described in section Locational adverbs.
Words like vehnä (wheat), heinä (hay), herne (pea), and villa (wool) are used both in singular and in plural in Finnish. In old language, singular was used to refer to crop as it grows or is being harvested, e.g. vehnä on laossa (the wheat field lays flat) and tehdä heinää (to make hay). In other contexts, plural was mostly used, e.g. myydä vehniä (to sell wheat). However, singular has become common, especially in trade: myydä vehnää.