手早い答え
só は「〜だけ」と「一人で」の両方、apenas は曖昧さなく「〜だけ」を意味します。
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
só
only or alone
Use só for restriction in everyday speech, or being without company.
apenas
only or merely
Use apenas for neutral restriction of an amount, fact, or action.
選び方
- só: Choose só if the sentence points to restriction in everyday speech, or being without company.
- apenas: Choose apenas if the sentence points to neutral restriction of an amount, fact, or action.
例文
Hoje eu estou só.
Today I am alone.
Tenho apenas dez reais.
I have only ten reais.
よくある落とし穴
The adjective só changes for plural when it means alone: elas estão sós. The adverb meaning only does not change.
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sóで、もう一度はapenas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。