Explanation
Use "might have", "may have", and "must have" to guess about something in the past. "Might have" and "may have" mean it is possible. "Must have" means you are almost sure.
For example, "He must have forgotten the meeting." "He" is the person, "must have forgotten" is the guess about the past, and "the meeting" is what he forgot. In Japanese, you may say "〜たかもしれない" or "〜たにちがいない", but English needs "have + past participle" after the modal when the guess is about the past.
過去のことを推量するときに "might have", "may have", "must have" を使います。"might have" と "may have" は「〜したかもしれない」という弱い推量です。"must have" は「〜したにちがいない」という強い推量です。
例えば "He must have forgotten the meeting." では、"He" が主語、"must have forgotten" が過去への強い推量、"the meeting" が忘れたものです。日本語では「〜たかもしれない」「〜たにちがいない」と言いますが、英語では過去の推量に "have + 過去分詞" が必要です。
Examples
- I might have left my wallet on the bus. バスに財布を置き忘れたかもしれません。
- She may have already called you. 彼女はもうあなたに電話したかもしれません。
- He must have worked late last night. 彼は昨夜、遅くまで働いていたにちがいありません。
- They might have taken the wrong road! 彼らは道を間違えたのかもしれない！
- We may not have enough time. 私たちは時間が足りないかもしれません。
- You must have been very tired. あなたはとても疲れていたにちがいありません。
Common Mistakes
Japanese learners often leave out "have" after the modal, for example "He might went home." The correct form is "He might have gone home." Another common mistake is using "must" as if it only means obligation, but in this pattern "must have" means a strong guess about the past, as in "She must have been busy."
日本人学習者は、助動詞のあとに "have" を落としやすいです。例えば "He might went home." は誤りで、正しくは "He might have gone home." です。また、"must" を「義務」だけで考えてしまうこともありますが、この形の "must have" は過去についての強い推量です。例えば "She must have been busy." のように使います。