Learn Icelandic: Hættu þessari vitleysu strax!

The verb hætta (to stop) governs the dative case when it takes a noun as its object. Because vitleysa is a feminine noun, both the demonstrative pronoun þessi and the noun itself change to their dative feminine singular forms, becoming þessari vitleysu.

Why does the verb hætta become hættu in this sentence?

This is the imperative (command) form. In Icelandic, the singular command is formed by merging the verb stem with the pronoun þú (you). For this verb, the combination of the stem hætt and the pronoun þú fuses together to become hættu.

How is the word vitleysa constructed?

It is a compound built from vit (sense, intelligence, or wit) and the suffix -leysa (indicating a lack of something, similar to the English suffix '-lessness'). Literally, it means 'senselessness', but it is the standard word for 'nonsense' or 'stupidity'.

How would the sentence structure change if I wanted to say 'Stop talking nonsense' using a verb instead?

When hætta is followed by an action rather than a noun, it requires the particle að plus an infinitive verb. You would say Hættu að tala vitleysu! Notice that in this new sentence, vitleysu is in the accusative case because it is now the direct object of tala (to speak), rather than being governed by hætta.