11 puzzles from Raymond Smullyan, each explained in a minute and credited to the original work. Free on Savvy.
Two doors: one leads to freedom, one to doom. Two guards: one always tells the truth, one always lies — you don't know which is which. You may ask one guard a single question. What…
— Raymond Smullyan, What Is the Name of This Book? (knights-and-knaves puzzles)
A suitor must choose between a gold casket and a silver casket; one contains the treasure. The gold casket reads: 'The treasure is in this casket.' The silver casket reads: 'Exactl…
— Raymond Smullyan, The Lady or the Tiger? And Other Logic Puzzles
A king's dungeon has two doors. Behind one waits a lady; behind the other, a hungry tiger. Door One reads: "IN THIS ROOM THERE IS A LADY, AND IN THE OTHER ROOM THERE IS A TIGER." D…
— Raymond M. Smullyan, The Lady or the Tiger? and Other Logic Puzzles
You meet three islanders: one is a knight who always tells the truth, one a knave who always lies, and one a spy who can say either. Red says 'I am a knight.' Blue says 'Red is tel…
— Raymond Smullyan, What Is the Name of This Book?
In Smullyan's Transylvania, every inhabitant is a human (always truthful) or a vampire (always lying) — and separately, either sane (correct about what's true) or insane (convinced…
— Raymond Smullyan, What Is the Name of This Book? The Riddle of Dracula and Other Logical Puzzles
Assume a pub has at least one person who might, at some point, order a drink. Logician Raymond Smullyan claimed there's always at least one patron such that, if that particular per…
— Raymond Smullyan, What Is the Name of This Book?
A gold casket reads: 'The portrait is in this casket.' A silver casket reads: 'The portrait is not in this casket.' A lead casket reads: 'The portrait is not in the gold casket.' Y…
— Raymond Smullyan, What Is the Name of This Book?
Raymond Smullyan's island has two kinds of people: the sane, who believe only true things, and the insane, who believe only false things, and everyone always says exactly what they…
— Raymond Smullyan, What Is the Name of This Book? The Riddle of Dracula and Other Logical Puzzles
In a forest of talking birds, calling one bird's name to another makes it call back the name of some bird in reply. A 'mockingbird' always responds to any bird's name by calling ba…
— Raymond Smullyan, To Mock a Mockingbird and Other Logic Puzzles
In the Forest of Forgetfulness, the Lion lies every Monday, Tuesday, and Wednesday and tells the truth the other four days. The Unicorn lies every Thursday, Friday, and Saturday an…
— Raymond Smullyan, What Is the Name of This Book? The Riddle of Dracula and Other Logical Puzzles
The sugar has gone missing, and it was either the Duchess or the Cook — no one else. Everyone agrees on one house rule: whoever stole the sugar is certain to lie about it afterward…
— Raymond Smullyan, Alice in Puzzle-Land: A Carrollian Tale for Children Under Eighty