Definition from Wiktionary, the free dictionary
See also: Appendix:Variations of "ko"
-kö (in words that include front vowels ä, ö, y or the vowels i or e alone)
- (enclitic) Turns any word into an interrogative. When appended to a verb, it corresponds clauses formed with e.g. do, does, don't, and doesn't in English or the inversion with auxiliaries. When appended to another word, it is expressed in English by intonation or eh.
- (enclitic) In indirect questions, -kö appended to the verb corresponds the conjunctions if and whether in English.
- (enclitic) With the negation verb (en, et, ei, emme, ette, eivät) and the particle -hän (hän required by the vowel harmony), expresses "I suppose".
- (enclitic) With the particle -hän (hän required by the vowel harmony), expresses "I wonder if".
- (interrogative particle) The particle -kö is used when there is no other interrogative word, in both direct and indirect questions. The answer is expected to be simply affirmative or negative.
- (I wonder if) Note that, unlike in English, the sentence meaning "I wonder if" is an interrogative sentence in Finnish, so it ends with a question mark.