Let's say my friend has a fly on her head, but she does not know it.
I say to her: "You don't know that you have a fly on your head".
Right before I uttered my statement - it was true, but right after I uttered it - it was false.

Was I lying?

2 Answers 2


No. Lying implies an intent to deceive. To speak a falsehood is not necessarily to lie.

As for the truth-status of the statement, it's not at all paradoxical; it's just temporally bound.

  • Yet I knew in advance that by uttering my statement I will make it false, does that not count as an intent to speak falsehood? Also, I understand there is no problem with the truth-status of the statement, but there is an ambiguity as to whether it was false while I was uttering it, which I believe is the criterion for speaking falsehood.
    – Joe
    Commented Jan 9, 2012 at 8:21
  • 2
    You knew that when you were saying it, it would be true until the listener received the message, at which point it would become false. That is not an intent to deceive. Temporal paradoxes like this abound; is there something particular that interests you about this? Commented Jan 9, 2012 at 8:35
  • In fact there is. I asked this question to settle a disagreement I had with other commenters around this question regarding the surprise exam paradox (a.k.a. the unexpected hanging paradox). I argued that the teacher was lying when he was promising the students a surprise exam during the year, because once he gave them this information the exam is no longer guaranteed to be a surprise. Alas, as you have shown me, I was wrong. Thank you!
    – Joe
    Commented Jan 9, 2012 at 8:48
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    Glad to be of help. You may find the SEP article on Epistemic Paradoxes interesting, in that case: plato.stanford.edu/entries/epistemic-paradoxes Commented Jan 9, 2012 at 9:41

The timing of the statement is not paradoxical at all. If you state truthfully that someone doesn't know something, then you haven't lied in uttering that statement. The fact that the target of your statement will then know what they didn't previously cannot undo the truth that was uttered in the past. If you repeat the statement however, then you would be uttering a false statement due to the other person subsequently being in possession of that knowledge.

Let's mix this up a bit. You are about to tell your friend that she has a fly on her head, and you knew a moment ago that she was not aware of this, but as you are about to utter your statement, your friend sees the fly in a reflection. You then say "you don't know there is a fly on your head". Have you lied?

Clearly not. Your knowledge may be in error and the statement false, yet this does not make your statement a lie. This I think is the crux of Michael Dorfman's answer.

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