Answer to the Friday Puzzle….


Over the weekend Jon Ronson, Rebecca Watson and I announced our Paranormal Road Trip.  It will happen towards the end of October and involve us driving from Buffalo to Nashville investigating odd stuff.  We are on the look-out for weird things to examine and visit, so please submit your ideas via the project website.

On Friday I set this puzzle……

Yesterday I met a man called Bill.  Bill said ‘I always lie’.  Was Bill lying or telling the truth?

If you have not tried to solve it, have a go now.  For everyone else the answer is after the break.

Bill is lying.  His statement cannot be true because it would be self-contradictory.  It must be the case that Bill sometimes lies and sometimes tells the truth.

Did you solve it?  Any other answers?

I have produced an ebook containing 101 of the previous Friday Puzzles! It is called PUZZLED and is available for the Kindle (UK here and USA here) and on the iBookstore (UK here in the USA here). You can try 101 of the puzzles for free here.


40 comments on “Answer to the Friday Puzzle….

  1. Mick says:

    Got it! Easy one…

  2. Roland says:

    So the answer is YES. He was lying or telling the truth.

  3. Roland or Not Roland says:

    In RolandWorld surely the answer is “YES or NO”

  4. Michael Sternberg says:

    Right. Bill’s statement must be a lie, which means that its opposite is true: “I do not always lie.” The “always” is key, bypassing a Liar paradox.

    • David D says:

      What would we do without you here to repeat the answer to us each week…

    • Anonymous says:

      I agree with you DD.
      I was just sitting here, totally confused, all at sixes and sevens, till Michael’s clarification came in – and, let’s face it – it was a particularly taxing conundrum last Friday.
      Hero isn’t a word I use very often, but in this case I think it is apposite.

    • Michael Sternberg says:

      Aren’t you the least bit interested to look a little beyond the puzzle at hand? You might learn something at the link.

      While we are at it, David’s statement about “each week” is clearly wrong, as I did not do so last week. The preceding statement demonstrates, of course, the use of a counterexample.

  5. Ian says:

    Cheers, Richard and, yep, got that one right 🙂 Thanks for another delightful brain workout. Have an excellent week 😀

    • Anonymous says:

      Maybe instead of “The Friday Puzzle” Richard should call it the “Five Second Brain Workout”?

  6. Anonymous says:

    Maybe, instead of “The Friday Puzzle” Richard should call it the “Five Second Brain Workout”?

  7. gw says:

    If Bill was permanently bed bound and was commenting on his state of permanent prostration, he would be telling the truth.

    • One Eyed Jack says:

      That would be “lay”, not “lie”.

    • Sorry, Jack. ‘Lie’ is the intransitive verb, and when I am in bed, I lie there. ‘Lay’ is transitive. Confusingly, the past tense of ‘lie’ is ‘lay’ (‘I lay in bed all day last Sunday’) but that doesn’t make any sense here.

  8. Eddie says:

    Not sure I like the ‘solution’. It seems to be wriggling out of facing the paradoxical nature of the situation pointed out by others on Friday.

    • Stevie says:

      I think the solution is sound. The problem could be if people haven’t read earlier puzzles set on the street where some residents always tell the truth, others always lie and a third group do both. I assumed that Bill lived on that street, hence it being logical (to me) to assume Bill would be from one of the three groups mentioned.

    • Paul Durrant says:

      The paradoxical statement would

      “I am lying in this statement”

      “I always lie” doesn’t refer to itself in the same way.

    • Photon Boy says:

      I don’t see any wriggling going on. This is not a paradox. It is a simple straightforward puzzle.

    • Gus Snarp says:

      See, someone did need Michael Sternberg’s explanation. Look above and read it. If that doesn’t work, try this:

      If Bill were telling the truth, that would be paradoxical. In fact, it would be logically impossible. You made the mistake (and I made it at first as well, but happened to realize I had inserted it when I started carefully parsing the logic) of assuming a condition that was very intentionally left out, namely that if Bill is telling the truth, then he always tells the truth. There was no reason to assume that, but familiarity with that sort of puzzles locked you in to that precondition existing when, in fact, it did not.

      There’s no wriggling here. If Bill says he always lies, that statement MUST be a lie. Nothing else matters. Therefore, he could not be telling the truth. The logic that follows is unnecessary to contemplate to have solved the puzzle, but it follows that if he is lying about that statement, then he does not always tell the truth either, but that question wasn’t asked. What was asked is whether he was lying with that one statement. From the fact that he was lying about the statement, and the nature of the statement, it follows that he sometimes lies and sometimes tells the truth: in other words, Bill is a perfectly ordinary person in terms of honesty. But you assumed a kind of person we never meet in the real world, one that only exists in convoluted logic puzzles. But this puzzle was not convoluted, it was quite straightforward.

  9. Stephen says:

    I figured he was speaking the truth, but meant that he always lies down, never standing nor sitting.

  10. Yep, that’s the conclusion I landed on as well. Just because he’s lying, doesn’t mean his statement has to be the *exact* opposite of the truth.

  11. Aha a puzzle I solved as a seven year old when first exposed to it in the classic Star Trek episode “I, Mudd”

  12. Kanzie says:

    I say Bill is telling the truth. He might be quadriplegic and is always on a bed.

  13. Lazy T says:

    I always lie when telling the truth, and always tell the truth when lying,
    mostly I’m just confused..

  14. Laith says:

    Yup an easy one for me, for a change.

  15. The real riddle here is: how do we even know if his name is actually Bill? How many more sleepless night will you make us endure, Richard, before ending this foul uncertainty? Oh, the lamentations! Must we be doomed to suffer our way through life thinking he might, in truth, be a Pete?

    Or Steve.

    Or Walter.

  16. Tomas Blomberg says:

    I see four scenarios, but we are not told which one we are in:

    1. Bill has always told the truth before he spoke the sentence.
    2. Bill has told both lies and truths before he spoke the sentence.
    3. Bill has always lied before he spoke the sentence.
    4. Bill has said nothing before he spoke the sentence.

    Did I miss any possibilities?

    In case 1, it’s clear that he is lying when he says “I always lie”, since he doesn’t always lie.
    In case 2, it’s clear that he is lying, since he doesn’t always lie.
    In case 3, if he is lying now, it means that he is sometimes telling the truth, but that is obviously not the case since he has never said anything true. Therefore it can’t be a lie. Can it be true? Of course not, since that would directly imply that it’s actually not true.
    In case 4, if he is lying now, it means that he is sometimes telling the truth. Since this is the only sentence he has ever said, this sentence has to be the one that’s true. So can his only sentence ever be true? No, for the same reason as in case 3.

    In other words, I don’t know. He is either lying, or neither lying or telling the truth.

  17. Anonymous says:

    Well done Tomas
    Can anyone come up with an even longer way of saying that Richard got the right answer?

    • Tomas Blomberg says:

      Richard wrote “Bill is lying.” Richard seems to say that it’s impossible that Bill said something self-contradictory. Which I just showed is very possible. In other words, Richards answer is wrong. We don’t know if Bill is lying or simply said something self-contradictory.

      Maybe you can come up with a longer way of explaining why Bill couldn’t possibly have said something self-contradictory? Isn’t he allowed to have never said anything before that statement? Isn’t he allowed to have lied every time before that statement?

    • Anonymous says:

      Sorry Tomas.
      It’s shorter.
      You haven’t broken your own record this time

  18. EspeceDeSuissesse says:

    hah! got it – between filling the washing machine and heading off to work. my, but there’s a lot of competitive horn-locking on this thread!

  19. Hugh Janus says:

    Solved it. Took me less than 5 seconds

  20. Chuffy the Horse says:

    As a horse, I figured this out very quickly. Richard, your puzzles are always a delight.

  21. The second comment said “yes,” would be the answer; actually the answer is “no.”

  22. Of course, You realize that no self-respecting liar would admit that he was a liar.

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