for と since の使い分け For or Since?
前置詞 Prepositions
for は期間の長さ(for three years =3年間)、since は始まりの一点(since 2023 =2023年から)。「どれだけ」なら for、「いつから」なら since。現在完了の相棒コンビです。
For measures how long (for three years); since names the starting point (since 2023). Length → for. Starting line → since. They're the present perfect's favorite partners.
長さの for、始点の since
For the Span, Since the Start
数直線をイメージしてください。for の後ろには「線の長さ」が来ます(for ten minutes / for a week / for ages)。since の後ろには「線の左端」が来ます(since Monday / since 2020 / since I was a child)。since は「そこから今まで」を含むので、現在完了と組むのが基本です。
Picture a number line. After for comes the line's length: for ten minutes, for a week, for ages. After since comes the line's left end: since Monday, since 2020, since I was a child. Because since sweeps from that point up to now, it pairs naturally with the present perfect.
同じ事実を2通りで One fact, two framings
I've had this bike for ten years.
この自転車は10年使っている。
10年という長さ。 The length: ten years.
I've had this bike since high school.
この自転車は高校のときから使っている。
高校という始点。同じ事実の別の切り取り方。 The starting point — the same fact, framed from the other end.
She's been on the phone since noon.
彼女は昼からずっと電話中だ。
始点+「今もまだ」の含み。 A starting point — plus the hint that it's still going.
for + 期間
後ろは「〜間」と言える長さの言葉。 What follows for answers "how long."
We talked for two hours.
2時間話した。
since + 起点
後ろは時点。文(since I moved here)も置ける。 What follows since is a point in time — even a clause: since I moved here.
Everything has changed since I moved here.
引っ越してきてから、すべてが変わった。
よくある間違い Common Mistake
I've lived here since three years.
ここに住んで3年です。(のつもりで)
I've lived here for three years.
ここに住んで3年です。
three years は「長さ」なので for です。since を使いたいなら、起点の形(since 2023)に変えます。
Three years is a length, so it takes for. To keep since, turn it into a starting point: since 2023.
- for a while しばらく ぼんやりした長さも、長さは長さ。for の守備範囲。 Even a vague length is still a length — for's territory.
- since then それ以来 直前に話した出来事を、そのまま起点にする便利ワード。 It recycles what you just said as the starting point.
- ever since それからずっと since の線を「途切れずずっと」と強調した形。 Since's line, underlined: unbroken the whole way.
- for now 今のところは 「当面の間」という短い線。for 専用のイディオム。 A short line reaching just ahead — a for-only idiom.
まとめ Summary
- 「どれだけ」= for、「いつから」= since。 How long → for. Since when → since.
- since は「そこから今まで」込み。現在完了と組む。 Since sweeps up to now — it runs with the present perfect.
- for は過去形とも組める(I lived there for ten years.)。 For also works with the plain past: I lived there for ten years.
- 長さの言葉が来たら for に切り替え(× since three years)。 A length after since is the classic slip — switch to for.