手早い答え
em vez de はあらゆる置き換え、ao invés de は選択肢が反対のときに最も正確です。
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
em vez de
instead of
Use em vez de for substitution: one action, person, or thing takes another’s place.
ao invés de
as the opposite of
Use ao invés de for a genuine reversal or opposition between directions, states, or results.
選び方
- em vez de: Choose em vez de if the sentence points to substitution: one action, person, or thing takes another’s place.
- ao invés de: Choose ao invés de if the sentence points to a genuine reversal or opposition between directions, states, or results.
例文
Fomos de ônibus em vez de carro.
We went by bus instead of by car.
Ao invés de cair, a temperatura subiu.
Instead of falling, the temperature rose.
よくある落とし穴
Broad use of ao invés de is common, but em vez de is always the safer expression when there is substitution without opposition.
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em vez deで、もう一度はao invés de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。