Case forms used to express time

When expressing a moment, interval, or duration of time, locational cases are mostly used, depending on the type of expression:

• the essive is used about years, e.g. tänä vuonna (this year), vuonna 2015 (in 2015), vuosina 2015–2020 (in 2015–2020); in this context, the consonant-stem form vuonna of vuosi is used (instead of the normal vuotena)
• the essive is used about seasons when they have an attribute, e.g. ensi talvena (next winter), kauniina kesinä (in beautiful summers); but e.g. talvella (in winter)
• the essive is used about days, e.g. viidentenä päivänä (on the fifth day), tiistaina (on Tuesday), vappuna (on the first of May), as well as multiday feasts, e.g. jouluna (at Christmas), and consecutive days, e.g. viikonloppuna (during weekend)
• the inessive is used about months, e.g. viime kuussa (last month); the adessive also possible, but much less common, e.g. tammikuussa ∼ tammikuulla
• the inessive is used about duration, e.g. Tein sen tunnissa (I did it in an hour)
• the inessive expresses the scope of repetition, e.g. kolme kertaa päivässä (three times a day)
• the nominative is used to express regular repetition, e.g. joka aamu (every morning), joka kesä (every summer), joka toinen päivä (every second day)
• the nominative is also used when a numeral and unit of time are used to express a duration, e.g. asuin siellä kolme vuotta (I lived there for three years); here the numeral kolme is in the nominative, and the associated noun is in the partitive, according to general rules for numerals
• in informal language, the nominative is often used when the essive is the correct case, e.g. Ville lähti viides päivä, more correctly Ville lähti viidentenä päivänä (Ville left on the fifth day)
• the nominative can be used about exact time of day, e.g. kello kaksi (2 o’clock, usually meaning PM), as an alternative to the ablative, as explained in the next item
• the ablative can alternatively be used about exact time of day, e.g. kello kahdelta and puoli kuudelta (half past five); it is especially used about scheduled events, e.g. kokous alkaa puoli kuudelta (the meeting starts at half past five), but the nominative is also used in such contexts, e.g. kello kaksi and puoli kuusi
• the ablative is used to express that something ends for some period of time, e.g. Lopetamme tältä päivältä (We’ll end for this day)
• the ablative indicates the origin of something in time, e.g. Tämä viini on vuodelta 1998 (This wine is from year 1998)
• the ablative is also used, as an alternative to the elative, for a starting time especially when relating to festivities, e.g. juhannukselta ∼ juhannuksesta aloitan lomani (on Midsummer day I will start my vacation)
• the genitive (in singular) or the nominative (in plural) is used to express that something lasts an entire period, e.g. Olin siellä koko tammikuun (I was there the whole January) and Teimme sitä kaikki päivät (We did that all days long)
• the partitive is used in negations of expressions described in the previous item, e.g. En ollut siellä koko tammikuuta (I did not spend there the whole January)
• the partitive is also used, in plural, to express durations using units of time, e.g. asuin siellä vuosia (I lived there for years) and asuin siellä useita vuosia (I lived there for several years)
• the elative and the illative are used to express a “from… to…” range, e.g. kello kahdesta kello kolmeen (from 2 o’clock to 3 o’clock) or just kahdesta kolmeen; they can also be used as standalone, e.g. Olen ollut täällä kello kahdesta (alkaen) (I have been here since 2 o’clock) and Olen täällä kello kolmeen (asti) (I will be here until 3 o’clock)
• the elative is used in some contexts for compound words expressing time where the first part is alku- (early, neart the start) or loppu- (late, near the end) or one of the parts second part expresses time (period) of the day or season, e.g. alkuvuodesta (near the start of the year) and iltayöstä (towards midnight); also aamusta ∼ aamulla (in the morning)
• the elative is also used in some sayings like pitkästä aikaa (after a long time); note that this an incongruent expression (elative with partitive)
• the illative is also used in a negative context, to express a duration of time when something has not happened, e.g. En ole tavannut häntä vuosiin (I have not met him for years)
• the translative is used in the meaning “for”, e.g. kesäksi (for summer) or viikoksi (for a week) and also aluksi (for a start), lopuksi (lastly), ensiksi (first), seuraavaksi (next), viimeksi ∼ viimeiseksi (last), ensimmäiseksi (first), toiseksi (second) etc.
• the translative can also mean “by…”, “at the latest in…”, e.g. Teen sen maanantaiksi (I will for it by Monday, i.e. so that it is available on Monday)
• otherwise mostly the adessive is used, e.g. aamulla (in the morning), ensi viikolla (next week), 1900-luvulla ∼ 20. vuosisadalla (in the 20th century), keskiajalla (in the Middle Ages)

When referring to time by some event or person, Finnish normally uses the word aika (time) preceded by a genitive, e.g. energiakriisin aika (the period of the energy crisis) and Kekkosen aika (Kekkonen’s time). To form an adverbial corresponding to a “during…” expression, the word aika is usually put in the essive: energiakriisin aikana. The word aika may also appear in the genitive, but then the meaning is “during the entire time of…”; it is often accompanied by the (uninflected) adjective koko (whole, entire), e.g. koko Kekkosen ajan.