Breakdown of Судя по акценту, оба брата — иностранцы.
брат
brother
иностранец
foreigner
оба
both (m/n)
судя по
judging by
Questions & Answers about Судя по акценту, оба брата — иностранцы.
Why is акцент in the dative case (акценту)?
It is governed by the preposition по. In the evidence-indicating phrase судя по (judging by), this preposition requires the Dative case to show what the judgment is based on. The word судя itself is an adverbial participle formed from the verb судить (to judge).
Why is the word for brothers (брата) in the singular here, especially since its plural is usually the irregular братья?
The word оба (both) governs nouns exactly like the number two (два). This means masculine and neuter nouns following it must take the Genitive singular. Even though the plural of брат is irregular, its Genitive singular is the perfectly regular брата.
What exactly is the dash doing before иностранцы?
It replaces the present-tense verb to be (are), which is omitted in Russian. An em-dash is grammatically required here because both the subject phrase (оба брата) and the predicate (иностранцы) act as Nominative nouns.
Is the comma after акценту strictly necessary?
Yes. The phrase судя по акценту acts as an adverbial participle phrase. Strict Russian punctuation rules dictate that these phrases must always be isolated by commas from the main clause, regardless of where they appear in the sentence.