Breakdown of Han kan lyfta båda armarna.
han
he
kunna
to be able to, can
lyfta
to lift / to take off, lift off
båda
both (pronoun, e.g. both of them)
Questions & Answers about Han kan lyfta båda armarna.
Why does the sentence use armarna (the arms) instead of just armar (arms)?
In Swedish, the word båda (both) must be followed by a noun in its definite plural form. So, while we say "both arms" in English, the Swedish grammar rule requires "both the arms" (båda armarna).
Could I say båda två armarna instead?
No, you should just use båda here. You use båda when a noun directly follows it (like båda armarna). You use båda två (both of them) when it stands alone without a noun after it, for example: "Which arm?" - "Båda två!"
In English I might say "both his arms". Why isn't there a word for "his" here?
In Swedish, you generally don't use possessive words (like "his" or "my") for body parts or clothing if it is already obvious who they belong to. Because he is the one doing the lifting, Swedish just uses the definite form (armarna) to mean "his arms".
Why is the verb lyfta in its infinitive form instead of the present tense (lyfter)?
Because it comes right after the "helper" (modal) verb kan (can). Just like in English, where we say "can lift" (not "can lifts"), Swedish modal verbs are followed by the infinitive form of the main verb.