手早い答え
algum は対象を特定せず、nenhum は「一つもない」と否定します。
確実な見分け方は、英語から訳す前に、その単語の働きを見きわめることです。
それぞれの単語の働き
algum
some or any
Use algum for an unspecified person or thing, often in questions.
nenhum
no or not any
Use nenhum for the absence of even one person or thing.
選び方
- algum: Choose algum if the sentence points to an unspecified person or thing, often in questions.
- nenhum: Choose nenhum if the sentence points to the absence of even one person or thing.
例文
Você tem algum irmão?
Do you have any brothers?
Não tenho nenhum irmão.
I do not have any brothers.
よくある落とし穴
After a negative verb, nenhum is natural in Brazilian Portuguese. The double negative reinforces one negative meaning.
文脈の中で練習する
自分の実生活から文を一つ選び、二回書いてみましょう。一度はalgumで、もう一度はnenhumで。どちらも成り立ちそうなら、意味の違いを言葉にしてみましょう。