主語になる -ing(Swimming is fun.)Swimming Is Fun: The -ing Subject
不定詞・動名詞 / Infinitives & Gerunds
「泳ぐことは楽しい」は Swimming is fun. ——主語には -ing が自然です。To swim is fun. も文法的には正しいものの、現代英語では硬く、実際には It's fun to swim.(仮主語)に化けます。「主語は -ing、to は it の後ろへ」が実戦の型です。
"Swimming is fun" — the -ing form is the natural subject. To swim is fun is grammatical but stiff in modern English; in practice it turns into It's fun to swim, with the placeholder it. Working rule: subjects take -ing; the to-version rides behind it.
主語の席には「実体」を
The Subject Seat Wants a Thing
主語は「何について話すか」を置く席で、そこには名詞のような実体が座ります。行為を主語にしたければ、実体の形= -ing に固めるのが英語の流儀: Reading before bed helps me relax.(寝る前の読書はリラックスにいい)。矢印の to do を主語に座らせる形は古風・格言調に響くため(To err is human.)、現代の文はまず it に席を譲ります。
The subject seat holds what the sentence is about, and it wants a noun-like thing. To seat an action there, English solidifies it into -ing: Reading before bed helps me relax. Seating the arrow form instead sounds archaic or proverbial (To err is human), so modern sentences hand that seat to it.
実体化した主語Actions, solidified as subjects
Learning aなぜ a なのか【総称の a】「〜というものは」と種類全体を代表させる用法。特定の一つを指していない。 language takes time.
言語の習得には時間がかかる。
-ing 主語は単数扱い(takes)。An -ing subject counts as singular: takes.
Getting up early isn't easy in winter.
冬の早起きは楽じゃない。
句ごと主語にできる。The whole phrase rides in the seat.
It's fun to swim in theなぜ the なのか【世の中に一つしかない】太陽・空・世界のように、そもそも一つしかないものだから the。 sea.
海で泳ぐのは楽しい。
to 版は it に席を譲って後ろへ(empty-it 参照)。The to-version yields the seat to it and moves back.
Swimming is fun.
-ing 主語=現代の標準。活動の一般論に。The -ing subject — the modern default for generalizing about activities.
Cooking at home saves money.
自炊は節約になる。
It's fun to swim.
仮主語版。後ろに具体条件を続けやすい。The placeholder version — easy to extend with details.
It's hard to focus when it's this hot.
こう暑いと集中するのは難しい。
よくある間違い / Common Mistake
×Swim every day is good for your health.
毎日泳ぐことは健康にいい。(のつもりで)
○Swimming every day is good for your health.
毎日泳ぐことは健康にいい。
動詞の原形は主語の席に座れません。「〜すること」を主語にするなら、-ing で実体化するのが第一選択(または It's good to swim ... へ組み替え)。日本語の「泳ぐことは」の「こと」が、英語では -ing の役目だと考えると覚えやすいはずです。
A bare verb can't sit in the subject seat. To say "doing X is …," solidify with -ing — or rebuild as It's good to swim … Japanese 「〜こと」 does exactly the job -ing does; map them onto each other and the rule sticks.
Seeing is believing.百聞は一見にしかず。-ing 主語+ -ing 補語のことわざ。主語席の -ing の看板例。An -ing subject meeting an -ing complement — the pattern's proverb flagship.
No parking / No smoking駐車禁止/禁煙掲示の No + -ing =「〜という行為はゼロで」。実体化した行為に No を掛ける形。Sign grammar: No + the solidified act — zero instances allowed.
... is worth doing〜はやる価値がある-ing 主語と相性のいい述語。Anything worth doing is worth doing well.(やる価値のあることは、ちゃんとやる価値がある)A predicate that loves -ing subjects: Anything worth doing is worth doing well.
the -ing of ...〜すること(名詞用法の完成形)the signing of the contract(契約の調印)のように、-ing は完全な名詞にもなる。-ing can go fully noun: the signing of the contract.
まとめ / Summary
行為を主語にするなら -ing(Swimming is fun.)。Action as subject: -ing — Swimming is fun.
-ing 主語は単数扱い。-ing subjects count as singular.
to 版は It's ... to do に組み替えるのが現代標準。The to-version rides behind it: It's … to do.
To err is human 型は格言・スピーチ専用の額縁。To-subjects are gilt frames — proverbs and speeches only.