Which is the proper (i.e. grammatically correct) response?  

Alice: "The earth is flat, and the sky is green."

  Bob: "The earth is round, and the sky is blue."

Alice: "Can you provide indisputable proof of these claims?"

  Bob: "No. It's just something I happen to have observed."

  Bob: "No. It's just something I happened to have observed."

  • 2
    If you had used the plain infinitive to observe, you would need to use past tense happened. But because you're using the perfect infinitive to have observed, you should use present tense. Apr 15, 2017 at 12:26
  • Thanks, that's what I thought. But what is a plain/perfect infinitive?
    – voices
    Apr 15, 2017 at 13:15
  • 2
    to have observed is a perfect infinitive, because of the have. And I should have called to observe the simple infinitive, which is the standard terminology. The perfect infinitive also encompasses the past, so I happened to have observed would generally be used if you were talking about two past times – one time in the past that is the focus of the conversation, and earlier times in the past when you observed it. Apr 15, 2017 at 13:26
  • 1
    Although note that in speech, I happened to have observed is nearly indistinguishable from I happen to have observed. Apr 15, 2017 at 13:32
  • 2
    Either one is grammatically correct. Jul 15, 2017 at 3:43

2 Answers 2


As Peter Shor has written, only I happen to have observed is correct. Whereas have observed is perfect, it describes knowledge due to a past experience—similar to the Present Perfect tense. The verb happen, acting as stative verb, tells that the speaker is referring to his present knowledge.


  1. I happen to know your father.
    (I know your father.)

  2. I happen to have known your father.
    (I used to know your father.)

happen here emphasizes the random nature of this circumstance and the irrelevance of its causes to the conscious efforts of the three persons involved.

  • Last year, I happened to have observed that his comments were unreasonable.
    – Lambie
    Nov 22, 2019 at 19:10

From the corpus of the Longman Dictionary, it seems the general past tense form is ‘happened to do’. Although I think ‘happen to have observed’ sounds better in your example, as it is not really describing a past case.

(A search led me here because of the title, so I do not think my answer is completely irrelevant.)

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