完成式不定詞
完成式不定詞多數會出現在第三類條件句，用作完成條件式的一部分；但完成式不定詞也可用在其他句型上。完成不定詞的構成為：
to have + 過去分詞
如同現在式不定詞，有些時候必須用上不帶 to 的被動語態不定詞，因此 to 會被省略掉。這種情況會發生在多數情態助動詞後，以及用在其他使用零不定詞的地方。
舉例
- He pretended to have seen the film.
- Before I turn 40, I want to have written a book.
- I would like to have been to the Taj Mahal when I was in India.
- If I had known you were coming I would have baked a cake.
- Someone must have broken the window and climbed in.
- That man may have noticed the bank robbers' getaway car.