Breakdown of A fronteira é protegida pelos soldados.
ser
to be
por
through / by / for / because of
proteger
to protect
a fronteira
the border
o soldado
the soldier
Questions & Answers about A fronteira é protegida pelos soldados.
Why does the verb end in "-a" (protegida) if soldiers (soldados) is masculine?
In the passive voice, the past participle (protegida) acts like an adjective and must agree with the subject of the sentence, which is the thing receiving the action. Because a fronteira (the border) is feminine and singular, the participle must be protegida. It doesn't matter that the soldiers doing the protecting are masculine.
Why do we use pelos to mean "by the"?
In Portuguese passive voice, the preposition por is used to mean "by" when introducing the agent (who or what is doing the action). Because soldados is masculine and plural, it requires the definite article os (the). When you combine por + os, they contract to form the word pelos.
Could I use está instead of é in this sentence?
You need é (from the verb ser) to form the true passive voice when describing an action actively being done by a specific agent. If you used está (from estar), you would be describing the resulting condition ("The border is currently in a protected state"), and you would normally drop the "by the soldiers" part entirely.
How would you flip this sentence back into the active voice?
You would make "the soldiers" the subject and use the regular present tense of the verb proteger: Os soldados protegem a fronteira. (The soldiers protect the border). Notice how the active voice focuses on who is doing the action, while the passive voice focuses on what is receiving it.
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