• The Infinitive as the Subject.

    When the Infinitive is used as the Subject, it is usually placed after the predicate and the sentence is introduced by the introductory it.

    It is very hard to work under such conditions.
    Очень трудно работать в таких условиях.

    However the Infinitive in this function can occur at the beginning of the sentence too.

    To collect all this information for such a short period of time would be completely impossible!
    Собрать столько информации и за такое короткое время было бы просто невозможно.

  • The Infinitive can be used as a part of the Compound Predicate.

    • Part of the Compound Nominal Predicate.

      The plan was to go the dean.
      План состоял в том, чтобы пойти к декану.

      Note: There is an interesting model where both the subject and the predicate are expressed by the Infinitive.

      To love is to believe.
      Любить - значит верить.

      To know is to understand.
      Знать - значит понимать.

    • Part of the Compound Verbal Modal Predicate.

      You should have told me about it yesterday.
      Тебе следовало сказать мне об этом вчера.

    • Part of the Compound Verbal Aspect Predicate.

      She began to cry.
      Она заплакала.

  • The Infinitive used as an object.

    I hate to ask people such questions.
    Ненавижу задавать людям такие вопросы.

    Note: Sometimes the introductory object it is used.

    He found it difficult to spot her in the crowd.
    Он обнаружил, что найти ее в толпе очень сложно.

  • The Infinitive can be used as an attribute.

    The captain was the last to leave the ship.
    Капитан был последним, кто покинул корабль.

    Notes:

    • The Infinitive is used attributively often acquires some modal meaning - the meaning of obligation or that of possibility.

      This is a book to read before going to bed.
      Это книга, которую можно читать перед сном.

      She gave him some documents to be signed immediately.
      Она дала ему документы на подпись, которые надо было немедленно подписать.

      He is not a man to make a woman happy.
      Он не тот человек, который может сделать женщину счастливой.

    • When the meaning is passive, the active form of the Infinitive is often used instead of the passive one here.

      There is no time to be lost = There is no time to lose.
      Нельзя терять время.

  • The Infinitive can be used as an adverbial modifier.

    • Adverbial modifier of purpose, often with the conjunctions in order and so as, especially when the meaning is negative.

      She put on her coat in order not to catch cold.
      Она надела пальто, чтобы не простудиться.

    • Adverbial modifier of result after the adverbs too, enough and sufficiently.

      Molecules are too small to see with an eye.
      Молекулы слишком малы, чтобы их можно было увидеть невооруженным взглядом.

    • Adverbial modifier of comparison with conjunctions as if, as thought.

      She began to talk loudly as if to show that she was not upset.
      Она начала говорить громко, как будто показывая, что не обиделась.

    • Adverbial modifier of attendant circumstances.

      An astronaut leaves the Earth and returns fifty years later to find his twin-brother quite an old man while he is still in the prime of his life.
      Астронавт покидает Землю и возвращается через 50 лет, при этом находит брата близнеца стариком, когда он сам в расцвете жизни...

  • The Infinitive can be used as parenthesis - to tell the truth, to begin with, to sum up, etc.

    To begin with we have not enough money to buy it.
    Начнем с того, что у нас недостаточно денег, чтобы это купить.

  • When used in the Objective-with-the-Infinitive construction, the Infinitive performs the function of part of a Complex Object.

    I saw him cross the street.
    Я видел как он переходил улицу.

  • When used with the Nominative-with-the-Infinitive construction, the Infinitive performs the function of part of the Compound Verbal Modal Predicate of special type (without modal verb).

    He is sure to be waiting for us.
    Он наверняка нас ждет.