Question 1

Why are the modal verbs plural (podem and devem) instead of singular (pode and deve)?

Accepted Answer

In this passive construction, the thing receiving the action (as enciclopédias) acts as the grammatical subject. Because this subject is plural, the modal verbs in both parts of the sentence must agree with it and take the plural form (podem and devem).

Question 2

Why is the pronoun se attached after Podem but placed before devem?

Accepted Answer

In European Portuguese, pronouns generally attach to the end of the conjugated verb, giving us Podem-se. But in the second clause, the negative word não acts as a magnet that pulls the pronoun to go before the conjugated verb, resulting in não se devem.

Question 3

Is it possible to attach the se to the infinitive verbs (usar and levar) instead?

Accepted Answer

Yes! When you have a conjugated modal verb followed by an infinitive, the pronoun can attach to either one. Podem usar-se is perfectly correct, as is não devem levar-se (though não se devem levar often sounds more natural to native speakers).

Question 4

Where is the subject in the second half of the sentence (mas não se devem levar para casa)?

Accepted Answer

The subject as enciclopédias is omitted in the second clause to avoid repetition. The plural form devem clearly signals that we are still talking about the encyclopedias, so we don't need to state the noun again.

Podem-se usar as enciclopédias aqui, mas não se devem levar para casa.

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