Breakdown of Hann þrífur alltaf lyklaborðið sitt.
hann
he
alltaf
always
þrífa
to clean
sinn
his/her/their own (reflexive possessive)
Questions & Answers about Hann þrífur alltaf lyklaborðið sitt.
Why do we use sitt here instead of hans for "his"?
This is the core difference between the reflexive pronoun sinn and the invariable word hans. Because the keyboard belongs to the subject of the sentence (hann), we must use a form of sinn to mean "his own". If the sentence said Hann þrífur alltaf lyklaborðið hans, it would mean he is cleaning another man's keyboard!
Why is the specific form sitt used?
The reflexive pronoun sinn has to match the gender, number, and case of the noun it belongs to. Lyklaborð is a neuter noun, and here it is in the accusative case because it is the direct object of the verb þrífur (cleans). The neuter, singular, accusative form of sinn is sitt.
Why does the noun have a "the" attached to it (lyklaborðið) if we are already saying it is "his" (sitt)?
Unlike English, Icelandic generally keeps the definite article on a noun even when a possessive pronoun follows it. The structure literally translates to "He cleans always the-keyboard his".
Why does alltaf (always) come immediately after the verb?
In Icelandic main clauses, adverbs of frequency like alltaf (always), aldrei (never), and oft (often) usually take the spot immediately following the conjugated verb, rather than sitting at the end of the sentence.