mikä (relatiivipronomini)

The relative pronoun mikä is essential for linking ideas in Finnish. Note that in Finnish, relative clauses are generally separated from the main clause by a comma, though the comma is optional for short, independent relative clauses (e.g., Teen mitä haluan). It is used in the following primary scenarios:

• Referring to a whole clause: When you comment on an entire preceding statement. In English, this is often 'which'.
  Hän unohti avaimet, mikä oli harmillista. (He forgot the keys, which was annoying.)
  Hän on rikas, mikä on totta. (He is rich, which is true.)
  This is also highly common with postpositions to express cause and effect, such as minkä vuoksi or minkä takia (which is why / because of which):
  Satoi, minkä vuoksi jäimme kotiin. (It rained, which is why we stayed home.)
• Referring to specific indefinite and demonstrative pronouns: It follows pronouns referring to things or abstract concepts, such as kaikki (everything), jokin (something), mikään (anything/nothing), and the demonstrative pronoun se (it/that). Note the crucial distinction: se, joka is used when referring to a person or concrete noun (e.g., se, joka tulee - the one who comes), while se, mikä is used for abstract events or things (e.g., se, mikä tapahtuu - that which happens).
  Tee se, mikä tuntuu hyvältä. (Do that which feels good.)
• Referring to superlatives and ordinal numbers: An abstract standalone superlative such as parasta takes mikä. An ordinal or limiter standing alone does not automatically do so: Olet ensimmäinen, joka kysyy refers to a person and takes joka. Choose by the referent, not merely by the absence of a written noun.
  Tämä on parasta, mitä tiedän. (This is the best [thing] that I know.) Note: When a superlative modifies a noun referring to a thing, both joka and mikä are fully acceptable in standard written Finnish (e.g., paras kirja, jonka ~ minkä olen lukenut - the best book that I have read). For people, use joka, including when a previously mentioned noun is omitted.
• Independent relative clauses: When there is no antecedent at all in the main clause, mikä acts independently (often translating to 'what' in English).
  Teen(,) mitä haluan. (I do what I want.)
• Referring to places (in local cases): Standard written Finnish explicitly accepts local cases of mikä (like missä, mistä, mihin) when referring to broad, abstract, or open-ended locations (such as a city or region). While jossa is preferred for specific concrete buildings, missä is fully accepted for broader areas.
  Hän varttui Kuopiossa, missä myös tapasi tulevan puolisonsa. (He grew up in Kuopio, where he also met his future spouse.)

Inflection: Like other pronouns, mikä must inflect to match its role in the relative clause. Its stem is mi- (e.g., missä, mistä, millä). The partitive form mitä is extremely common when the relative clause describes an ongoing action or an object of a partitive verb. The genitive/accusative form minkä is also essential, particularly for completed actions.

Spoken Finnish Note: In everyday spoken Finnish (puhekieli), mikä has a broader range than in standard writing and can replace joka in contexts where written Finnish uses joka. While common in speech, this should be avoided in standard written Finnish.

Pronoun with an Adjective
An abstract indefinite phrase can include an adjective: Tässä on jotain outoa, mitä en ymmärrä (There is something strange here that I do not understand).

Cause Phrases
The established combinations minkä vuoksi and jonka vuoksi can both link to the preceding situation; the same variation occurs with takia. This limited postposition pattern does not license joka oli harmi as a general whole-clause comment.