Learn Swedish: Jag vet att laboratoriet alltid städas av honom. - I know that the laboratory is always cleaned by him.

In Swedish passive sentences, the person or thing actually doing the action (known as the agent) is introduced by the preposition av, which means "by" in this context. So, av honom translates to "by him".

Why does the verb städas end in an "s"?

The -s at the end of the verb shows that it is in the passive voice. While städar means "cleans" (active), changing it to städas makes it "is cleaned" (passive). We use it here because the subject (laboratoriet) is receiving the cleaning, not doing it.

Why is the word order alltid städas instead of städas alltid?

Because this part of the sentence is a subordinate clause (a dependent clause starting with att). In a normal main sentence, adverbs like alltid (always) or inte (not) come after the verb. But in a subordinate clause, these adverbs must be placed before the verb.

What is the base form of the word laboratoriet?

The base form is ett laboratorium (a laboratory). In Swedish, ett-words that end in -ium drop the -um before adding the definite ending -et. That is why laboratorium becomes laboratoriet (the laboratory).