「今」の非現実は過去形で言います。If I were you, I'd apologize.(私があなたなら謝るね)。過去形なのに現在の話——これが仮定法過去の正体で、「過去形=現実からの距離」という原理の本丸です。
To talk about an unreal now, English uses the past tense: If I were you, I'd apologize. Past forms, present meaning — that's the so-called past subjunctive, and it's the headquarters of the past-equals-distance principle.
時間ではなく、現実からの距離
Not Time — Distance from Reality
If I had more time, I would learn the piano.(時間があればピアノを習うのに)。had は「昔」の意味ではありません。「実際には時間がない今」から一歩引いた、もうひとつの今を指しています。帰結側は would / could / might が受け持つ。「過去形で引いて、would で答える」——この1セットだけです。
If I had more time, I would learn the piano. That had isn't about the past — it points at an alternative now, one step removed from the real one where you have no time. The result clause answers with would, could, or might. Step back with the past form, answer with would: that's the whole kit.
もうひとつの今The alternative now
If I were you, I'd take theなぜ the なのか【その場で一つに決まる】話し手と聞き手のいる状況で、どれを指すか一つに決まるから the。日本語なら「（例の）」「うちの」を補って読むと感覚が近い。 offer.
私があなたなら、その話を受けるね。
忠告の定番形。if I were you は常に were。The classic advice frame — always were here.
If she were here, she'd know what to do.
彼女がここにいたら、どうすべきか分かるのに。
実際にはいない。だから過去形。She isn't here — hence the past form.
If we lived closer, we could meet every week.
もっと近くに住んでいたら、毎週会えるのにね。
帰結は could でもよい(可能の帰結)。The result can take could — ability in that other world.
If I have time
現実にありうる。「時間ができたら」。A live option: when I get the time.
If I have time tomorrow, I'll help you.
明日時間があったら手伝うよ。
If I had time
実際には無理そう。「あればなあ」。Wistful: I don't, and probably won't.
If I had time, I'd help you.
時間があれば手伝えるんだけど。
よくある間違い / Common Mistake
×If I am you, I will apologize.
私があなたなら謝る。(のつもりで)
○If I were you, I'd apologize.
私があなたなら謝るね。
「私があなたである」ことは現実には起こらないので、現実の if(現在形+will)では文が成立しません。非現実は過去形+would のセットで。if I were you はこの型の看板表現です。
You being me is never going to happen, so the real-if machinery (present + will) can't carry it. Unreality takes the past + would kit — and if I were you is its flagship phrase.
If I were you, I'd ...私があなたなら〜するね忠告の看板フレーズ。相手の椅子に仮に座ってみせる優しい形。The advice flagship — you borrow their chair for a moment, kindly.
if it weren't for ...〜がなければ「それが存在しない今」を仮定する型。If it weren't for you, I'd be lost.(君がいなかったら途方に暮れてる)Imagines a now without that thing: If it weren't for you, I'd be lost.
If only ...!〜でさえあればなあ!仮定法の if 節だけを感嘆に切り出した形。I wish の熱量高め版。The if-clause broken off as a sigh — I wish, with the volume up.
in your shoesあなたの立場ならIf I were in your shoes(あなたの靴を履いていたら)の比喩。忠告の相棒。From if I were in your shoes — advice's favorite metaphor.
まとめ / Summary
今の非現実=過去形+would。Unreal present = past form + would.
過去形は時間でなく「現実からの距離」。The past form marks distance from reality, not time.
be 動詞は were(仮定のランプ)。口語の was も普通だが書き言葉は were。Be becomes were — the hypothetical lamp. Casual was exists; write were.
If I were you, I'd ... を忠告の型として丸ごと持つ。Own If I were you, I'd … as your advice template.