Time Expressions and Collocations

English marks "when" with a small kit of prepositions — on Monday, at two, in the morning, last year. Finnish marks it by changing the ending of the time-word itself, and — this is the part that trips everyone — which ending depends on what kind of time-word it is. A weekday takes one case, a clock hour takes another, a part of the day takes a third. There is no single "when" ending to learn. This page collects the everyday time collocations you should memorise as fixed units, sorts them by the case each one demands, and shows the logic underneath so the pattern generalises. For the systematic case-by-case rules, lean on Time expressions overview, Essive for days and times and Telling the time.

Weekdays and named periods: the essive (-na / -nä)

To say "on Monday," Finnish puts the day in the essive — no word for "on" at all. The ending carries it.

The same essive names holidays and other whole periods — jouluna (at Christmas), juhannuksena (at Midsummer) — and it reappears on any specified time-noun: tänä aamuna (this [particular] morning), sinä päivänä (on that day). Bare, recurring seasons are the one exception, taking the adessive instead (see below). The full boundary is drawn in Essive for days and times.

"At" a clock hour: the ablative (-lta / -ltä)

To say something happens at a particular o'clock, Finnish uses the ablative — the same -lta / -ltä ending that otherwise means "from off." Think of the appointment as arriving "off" the clock face.

So "at two" is kahdelta (ablative of kaksi), "at ten" is (kello) kymmeneltä. You may keep kello in front of the number — kello kymmeneltä — or drop it. Note the harmony: kymmeneltä takes the front ending -ltä (the y is front-vowel), while kahdelta takes back -lta. This ablative-for-"at" is one of the most reliable places English speakers slip, because English "at" feels like a location, tempting kello kahdella — which is wrong. See Telling the time for the whole clock.

"Next" and "last": ensi + adessive/essive, viime + adessive/essive

For "next" and "last," Finnish keeps the modifiers ensi ("next") and viime ("last") uninflected, and inflects only the following time-noun — and the case it takes depends on the noun, matching whatever case that noun uses for "in/at" generally.

So viikko ("week") takes the adessive: ensi viikolla, viime viikolla. But vuosi ("year") and kesä ("summer") take the essive: ensi vuonna, viime vuonna, viime kesänä. Watch the irregular vuosi → vuonna — the essive is not vuosina here but the old fused form vuonna. You cannot reason this out from meaning; the case is a property of each noun, so learn viikolla vs vuonna as a pair.

Parts of the day: the adessive (-lla / -llä)

Bare parts of the day — morning, evening, night, daytime — take the adessive, the -lla / -llä "at" ending:

So: aamulla (in the morning), päivällä (in the daytime), illalla (in the evening), yöllä (at night). Seasons pattern with these — kesällä (in summer), talvella (in winter), keväällä (in spring), syksyllä (in autumn), all adessive. The rule of thumb: an unspecified, recurring part of day or season → adessive; a specified, one-off point → essive (tänä aamuna "this [particular] morning," sinä yönä "that night").

For "in the middle of the night," Finnish uses the postposition keskellä ("in the middle of") plus the partitive:

The bare adverbs: tänään, huomenna, eilen

A few of the highest-frequency time words are simply fixed adverbs — you neither add a preposition nor choose a case; you just say the word.

Tänään (today), huomenna (tomorrow), eilen (yesterday), plus ylihuomenna (the day after tomorrow) and toissapäivänä (the day before yesterday). Historically huomenna is an old essive and tänään an old form too, but you should treat them as unanalysable adverbs. Harmony note: huomenna is back-vowel (huomenna, not huomennä), while tänään is front — two neighbours on opposite sides of the harmony line, so do not let one contaminate the other.

Common Mistakes

Key Takeaways

• Finnish marks "when" by case, not prepositions — and the case depends on the class of the time-word.
• Weekdays and named/specified periods → essive (maanantaina, viikonloppuna, viime vuonna).
• "At" a clock hour → ablative (kello kymmeneltä, kahdelta) — never the adessive.
• "Next / last" → uninflected ensi / viime + the noun's own case: ensi viikolla (adessive) but ensi vuonna (essive).
• Bare parts of day and seasons → adessive (aamulla, illalla, yöllä, kesällä); keskellä yötä takes the partitive.
• tänään, huomenna, eilen are fixed adverbs — no case, no preposition. Mind the harmony split: huomenna (back) vs tänään (front).