By Michael Hartley
A terrible crime has been committed; the police have rounded up their suspects, and collected clues as to their innocence or guilt. The puzzle is: can you discover who should go free, and who will be detained?
Raymond Smullyan was an amazing inventor of logic puzzles, who filled dozens of books with them in his lifetime. In one book, called What is the name of this book?, he gives a puzzle where there are three suspects to a crime, and a small number of clues. The clues are of the form "if A is guilty, B is innocent", and so on, and it's possible to deduce everyone's innocence or guilty solely from the clues, using logic alone.
I like this kind of puzzle. If you do too, you'll keep coming back to this page and its "logic puzzle generator". Below, is a randomly generated puzzle like the one in Smullyan's book. Can you solve it?
If you think you know if someone is guilty or innocent, you can click on their name in the line-up below the clues. Keep clicking (or tapping) to toggle between "guilty", "innocent" and "unknown". When you've decided everyone's innocence or guilt, another button will appear allowing you to check your answers. There's also a link to generate a new puzzle, and change the number of suspects.
By the way, feel free to use the puzzles generated here any way you like. I only ask that, if at all practical, you give a link back to this page. For those of you who need a formal licensing agreement, you can assume that these puzzles are provided under a Creative Commons Attribution license. Also, do let me know how you use them! I love to hear from people who enjoy my puzzles, games and worksheets!
By the way, I have another page with a similar generator for a different kind of logic puzzle: one where you are accosted by a number of people, some perpetual liars, some unwavering truthtellers, and you have t figure out who is what.
Here are some tips for solving the puzzles on this page:
- Look for a pair of clues like "If A is guilty then B is guilty" and "If A is innocent then B is guilty." Then, it doesn't matter what A is, you know B is guilty.
- Likewise, if you see a pair of clues like "If C is guilty, D is guilty" and "If C is guilty, D is innocent," you know C can't be guilty, because that would mean D is both innocent and guilty!
- If you can't find pairs of clues like that, you can look for things like "If A is guilty, B is guilty" and "If B is guilty, A is innocent." Then, A can't be guilty, because that would mean, indirectly, that he (or she) would also be innocent. (Can you see why?)
- Once you've pinned down a few of the suspects, look at the clues you haven't used, and see what they tell you.
- The most important rule: have fun, and share these puzzles with friends who also like them!