Learn Icelandic: Strákurinn vaknar alltaf snemma, en ég vek hann stundum. - The boy always wakes up early, but I sometimes wake him up.

This sentence perfectly shows the difference between intransitive and transitive verb pairs. Vakna is intransitive, meaning it's an action the subject does on their own (the boy wakes up). Vekja is its transitive partner, an action the subject does to a direct object (I wake him up).

Is there a rule for how the root verb vakna changes to vekja?

Yes! Many transitive causative verbs are created from an intransitive base by shifting the root vowel. A root 'a' typically shifts to 'e', and a -j- is added to form the new infinitive (vekja). When conjugated for ég, the -j- drops out, leaving vek.

Why does vekja take hann as its object instead of honum?

While many verbs that affect other people take the dative case, vekja requires its object to be in the accusative case. The accusative form of the masculine pronoun is hann, which happens to look identical to its nominative subject form.

Why is the adverb stundum at the very end instead of before the verb?