- He locked the door to keep everyone out. （目的）
- They spoke quietly in order not to wake the children. （目的：in order to）
- We started our journey early so as to avoid the traffic. （目的：so as to）
［結果］
※動詞を修飾
- He grew up to be a doctor.
- The cat ran away, never to return.
- He woke up to find himself in the hospital
［感情の原因］
※形容詞を修飾
- We were happy to come to the end of our journey.
- I was surprised to hear her success of the experimentation.
- He was very excited to get a new game console.
［判断の根拠］
※形容詞を修飾
- You were clever to find the answer so quickly.
- She must be fool to believe such stories.
- It was careless of me to forget to lock the door. （性格、性質を表す場合には前置詞of）
［形容詞を修飾（補足説明）］
- Unfortunately, I was unable to work for over a week.
- I'm really tired. I'm ready to go to bed.
- This book is easy to read.
［程度］
※副詞を修飾
- The child was too small to reach the switch.
- The knife was not sharp enough to cut the string.
［関係詞+ to 不定詞（不定詞関係節）］
構造上は主語とbe動詞の省略と考える方が矛盾無く説明できるが、頻出の定型句となっているために便宜的に副詞用法とすることがある。
→関係代名詞（what / whom / which）を修飾する：形容詞用法
→関係副詞（where / when / how）を修飾する：副詞用法
- He's looking for an apartment where to live.
- I have forgotten the day when to submit the report.
- I got to know how to clean windows like a pro.
※日記 に補足があります。
→ 文法 #70 to不定詞（名詞用法）
→ 文法 #71 to不定詞（形容詞用法）
