手早い答え
faltar は必要量への不足、sobrar は必要量を超えて残るものです。
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
faltar
to be missing or insufficient
Use faltar for a needed amount, item, person, or time not being present.
sobrar
to be left over
Use sobrar for an amount remaining beyond what was used or needed.
選び方
- faltar: Choose faltar if the sentence points to a needed amount, item, person, or time not being present.
- sobrar: Choose sobrar if the sentence points to an amount remaining beyond what was used or needed.
例文
Faltam dez reais para pagar a conta.
We are ten reais short of paying the bill.
Sobrou comida para amanhã.
There was food left over for tomorrow.
よくある落とし穴
Portuguese often puts the quantity as the subject: faltam dez minutos and sobraram duas vagas.
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faltarで、もう一度はsobrar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。