A Gender-Biased Puzzle

This famous trick puzzle is very old:

Puzzle. The professor is watching across a field how the son of the professor’s father is fighting with the father of the professor’s son. How is this possible?

This puzzle is tricky only because of gender-bias. Most people assume that the professor is male and miss the obvious intended solution, in which a female professor is watching her brother fighting with her husband.

I just gave this problem on a test. Here are other answers that I received.

  • The professor is gay and is watching his brother fighting with his husband.
  • The professor is watching his brother fighting with the father of the professor’s step-son.
  • The father of the professor’s son is himself. So he is watching a video of himself fighting with his brother.

Years ago people couldn’t figure out this puzzle at all. So there has been progress. I was glad that my students suggested so many ideas that work. Nonetheless, many of them revealed their gender-bias by initially assuming that the professor is a man.

I can’t wait until this puzzle stops being tricky.



  1. Jonathan Kariv:

    A 1996 example https://www.youtube.com/watch?v=2zI-EXuYgm4

  2. gentleman:

    1) The whole puzzle is “gender biased” on purpose, in order to fool the person that tries to solve it. The words “father” and “son” are repeated 4 times in 12 non-article/trivial words.
    2) This puzzle works only in languages that don’t have a feminine for the word professor (like English). Is English a gender-biased language?

  3. David Bernier:

    The variant I heard is this:


    Many years ago, I was truly puzzled by this riddle…

  4. Philip Petrov:

    He watches his reflection while beating himself…

  5. rosie:

    Well done, that student who thought of a same-sex marriage. You didn’t mark it as wrong, did you? That would’ve been heterosexist if you had.

  6. tanyakh:

    Rosie, I gave full credit for every answer that made sense.

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