1. 仮定法過去…現在の事実に反する仮定を表す
    a. What would the world be like if we had nothing but water to drink?
    b. If I knew Judy’s new address, I could send her a birthday card.
    cf. As I do not know Judy’s new address, I cannot send her a birthday card.
  2. 関係副詞whenの非制限的用法
    a. In 1970, when the International Exposition was being held, my parents moved to Osaka.
    b. I arrived in Okinawa on May 7, when the rainy season started there.
    c. The custom goes back to the late eighteenth century, when she began to have tea and cake around 5 p.m.