Passive Se with Plural Modals
In Portuguese, the passive se is often used to express general rules or guidelines. When the noun receiving the action is plural, the verb must also be plural.
If the sentence uses a modal verb (like poder or dever) followed by an infinitive, the modal verb takes the plural form, while the main verb stays in the infinitive.
As usual, the pronoun se attaches to the end of the conjugated verb with a hyphen in affirmative sentences. "Trigger" words like não or the conjunction que pull the se directly in front of the modal verb.
| The encyclopedias can be used here, but they must not be taken home. | Podem-se usar as enciclopédias aqui, mas não se devem levar para casa. |
| It is a good thing that the old encyclopedias can be used. | Ainda bem que se podem usar as enciclopédias antigas. |
| These infractions must be strictly avoided. | Devem-se evitar estas infrações rigorosamente. |
Multi-word Modals
This agreement rule also applies to other verbs acting as modals, such as ter de (to have to) or costumar (to usually do). The conjugated verb pluralizes, and the se attaches directly to it (stepping right before the preposition de, if there is one).
| The sanctions have to be strictly imposed. | Têm-se de impor as sanções rigorosamente. |
| Severe sanctions are usually imposed for any infraction. | Costumam-se impor sanções graves por qualquer infração. |
Questions and Other Triggers
Question words (like quantas) also pull the se before the conjugated modal verb. Regardless of where the se sits, the modal verb must remain plural to match the noun.
| How many checkouts can be made at the same time? | Quantas requisições se podem fazer ao mesmo tempo? |
| The renewals cannot be made after the deadline. | Não se podem fazer as renovações depois do prazo. |