基本の説明Overview
動詞に -ing をつけると、「〜すること」という意味の名詞として使えます。これを動名詞と呼びます。名詞と同じように、文の主語・目的語・補語になれます（Playing the guitar is fun. のように）。Adding -ing to a verb makes a noun meaning “doing something.” This is called a gerund. Like any noun, it can be the subject, object or complement of a sentence (as in Playing the guitar is fun.).
前置詞のあとにも使えます（good at playing, Thank you for helping など）。前置詞のあとに動詞を置くときは、いつも動名詞にします。-ing の形は進行形（is playing）と同じですが、「〜すること」という名詞の働きをしているのが動名詞です。It can also follow a preposition (good at playing, Thank you for helping, etc.). When a verb comes after a preposition, it is always a gerund. The -ing form looks the same as in the progressive (is playing), but a gerund works as a noun meaning “doing.”
動名詞は不定詞（to + 動詞の原形）の名詞的用法とほぼ同じ意味ですが、動詞によってどちらを目的語にできるかが決まっています。次の表で整理しましょう。A gerund means almost the same as the noun use of the to-infinitive, but each verb decides which one it can take as its object. The table below sorts them out.
| 目的語にできるものWhat can follow | 動詞の例Verbs | 例Example |
|---|---|---|
| 動名詞だけGerund only | enjoy, finish, stop, practice, keep, mind | I enjoy reading. |
| 不定詞（to + 原形）だけTo-infinitive only | want, hope, decide, plan, need, would like | I want to read. |
| どちらも使えるEither one | like, love, start, begin | I like reading. / I like to read. |
-ing のつけ方にも注意しましょう。そのまま -ing をつけるのが基本（play → playing）で、e で終わる語は e をとり（make → making）、「短母音＋子音字1つ」の語は子音字を重ねます（swim → swimming, run → running）。Mind the spelling too. Usually just add -ing (play → playing); drop the final e (make → making); and double the last consonant after a short vowel (swim → swimming, run → running).
例文で確認Example sentences
① 主語になる動名詞（〜することは）1. Gerund as the subject (“doing ... is ~”)
② 補語になる動名詞（〜することだ）2. Gerund as the complement (“... is doing ~”)
③ 動名詞だけを目的語にとる動詞3. Verbs followed only by a gerund
④ どちらも使える動詞と、不定詞だけの動詞4. Verbs that take either, and verbs that take only a to-infinitive
⑤ 前置詞のあとの動名詞5. Gerund after a preposition
確認クイズQuick check
カッコの中の語を、文に合う形にして空所に入れましょう（to不定詞が正しい場合は to ... の形で答えます）。Change the word in the parentheses into the form that fits and write it in the blank (if a to-infinitive is correct, answer in the form to ...).
- I enjoy ___ tennis with my friends. (play)
答えを見るShow the answer
playing — enjoy のあとは動名詞だけ。After enjoy, use only a gerund. - He wants ___ a new bike. (buy)
答えを見るShow the answer
to buy — want のあとは不定詞だけ（buying は不可）。After want, use only a to-infinitive (buying is not possible). - ___ every day is good for your health. (swim)
答えを見るShow the answer
Swimming — 動名詞が主語。swim は m を重ねる。A gerund as the subject. swim doubles the m. - Thank you for ___ me. (help)
答えを見るShow the answer
helping — 前置詞 for のあとは -ing 形。After the preposition for, use the -ing form. - We finished ___ the room. (clean)
答えを見るShow the answer
cleaning — finish のあとは動名詞だけ。After finish, use only a gerund. - He stopped ___ when the teacher came in. (talk)
答えを見るShow the answer
talking — 「話すのをやめた」は stop -ing。“Stopped talking” is stop -ing.
おさえておきたいポイントKey points
- 動詞の -ing 形は「〜すること」という名詞の働きをする。主語・目的語・補語・前置詞の目的語になれるThe -ing form of a verb works as a noun meaning “doing.” It can be a subject, an object, a complement or the object of a preposition
- enjoy / finish / stop / practice / keep / mind のあとは動名詞だけAfter enjoy, finish, stop, practice, keep and mind, use only a gerund
- want / hope / decide / plan / need / would like のあとは不定詞（to + 原形）だけAfter want, hope, decide, plan, need and would like, use only a to-infinitive
- like / love / start / begin は動名詞・不定詞のどちらも使えるLike, love, start and begin can take either a gerund or a to-infinitive
- 前置詞のあとに動詞を置くときは、必ず動名詞にする（to不定詞にはしない）When a verb comes after a preposition, it is always a gerund (never a to-infinitive)
- -ing のつけ方：make → making（e をとる）、swim → swimming（子音字を重ねる）Spelling: make → making (drop the e), swim → swimming (double the consonant)