There are essentially two types of question words in Icelandic: interrogative pronouns and interrogative adverbs. The pronouns inflect for gender, number and case (see bin.arnastofnun.is for complete inflection tables) and can stand with a noun or another pronoun, while the adverbs do not inflect and always stand on their own.
This lesson contains a comprehensive list of all the question words (pronouns and adverbs), their translations and examples of usage. Then a section on responses, as well as a note on common confusion when translating between English and Icelandic.
This category only counts 4 words: hver, hvor, and hvaða, in addition to the largely outdated hvílíkur. Hver and hvor decline for gender, number and case, and can either stand with another word or alone. Hvaða does not change but always stands with another word.
Compared to the pronouns, the adverbs are simple. No gender, no number, no case, no hassle.
In addition to the interrogative pronouns and interrogative adverbs, there is an exclamation that is worthy of a sort of honourable mention. While nú is not technically a question word but an exclamation indicating surprise, it does tend to imply a strong expectation of an answer much like a question word.
Two outdated question words also exist: hví and hve. They have been replaced by af hverju, hvers vegna and hversu, hvað. These are rarely if ever heard in spoken language but may be used in written language or to make one’s speech sound archaic or extremely formal. The student of Icelandic may wish to be familiar with these words to recognise them when they appear.
There are four possible responses to the why questions af hverju, hvers vegna and til hvers: af því að, vegna þess að, til þess að and út af. Much as with the question words, af því að and vegna þess að are interchangeable, while til þess að underlines the purpose or end goal. Út af is the odd one out, only being used with a noun as a cause, and not a verb. Note the different uses.
In English, question words do double duty as conjunctions: that is, words that connect sentences.
Icelandic, however, has its own set of conjunctions, notably sem and þegar. Therefore, using the Icelandic question words outside of questions doesn’t work. The following table shows the question word in Icelandic and English, as well as the appropriate conjunction to use and an example.
Thinking about thinking. Do you think it's a meta article? What do you think of that? Learn the different ways to say "think" in Icelandic!