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If you're intrigued by puzzles and paradoxes, these 200 mind-bending logic puzzles, riddles, and diversions will thrill you with challenges to your powers of reason and common sense. Raymond M. Smullyan — a celebrated mathematician, logician, magician, and author — presents a logical labyrinth of more than 200 increasingly complex problems. The puzzles delve into Gödel’s undecidability theorem and other examples of the deepest paradoxes of logic and set theory. Detailed solutions follow each puzzle.

241 pages, Paperback

First published January 1, 1978

Raymond M. Smullyan was a logician, musician, Zen master, puzzle master, and writer.

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Displaying 1 - 30 of 60 reviews

December 22, 2015

I first read about Smullyan in one of Martin Gardner's books of mathematical puzzles. I'm a fool for torturing my brain with convoluted conundrums, so when I found a copy, I was overjoyed. I devoured it in a week, and was not disappointed.

This book contains Smullyan's famous logic puzzles about knights (who always say the truth) and knaves (who always lie) and all interesting combinations thereof. Apart from providing intellectual fixes for maths junkies, this book actually teaches logic through play. A serious perusal will ensure that one is a wiser person, by the time one reaches the end of the book.

This book contains Smullyan's famous logic puzzles about knights (who always say the truth) and knaves (who always lie) and all interesting combinations thereof. Apart from providing intellectual fixes for maths junkies, this book actually teaches logic through play. A serious perusal will ensure that one is a wiser person, by the time one reaches the end of the book.

March 8, 2008

Let's get the simple stuff out of the way: Yes, this is largely a book of Smullyan's well-known Knights and Knaves puzzles. However, it has a lot more.

Beginning and ending sections include jokes about logic and logicians that teach a huge amount about logic itself. A section in the back teaches about Godel's Theorem in a simple way anyone can understand (perhaps more elegantly than Hoftadter did, perhaps not). He gives a feeling for what logic is and why we understand it the way we do.

But back to the main thing: the puzzles. First, not all are Knights/Knaves. He has some (slightly silly) puzzles of other varieties (such as the title puzzle: what*is* the name of the book, after all?).

The Knights and Knaves puzzles are followed by other truth/not-truth variants. In increasing difficulty we get people who can lie or not, people who are insane and think true is false and false is true, people whose tendency to lie changes by the day of the week (which is something always unknown, of course) and take side trips into caskets with truth or lies on them and other variants.

The important piece there is "in increasing difficulty." This book is a disguised master course in boolean logic. Repeatedly, a puzzle will step back and ask you to solve a general case, without knowing exactly what situation it will be applied to.

By the end of the main puzzle section, we come to the actual Riddle of Dracula, which presents the problem of writing one solution that works for every puzzle up until then, across several chapters of the book. Smullyan isn't teaching how to solve a puzzle, he's teaching how the*system* of these puzzles works.

In the later chapters he discusses this openly and (lightly) applies the same principles to other varieties of puzzles, whch leads into his discussion of Goedel. That turns this book into a class not just on Boolean logic, but on the learning and the synthesis that form the basis of all science.

And it's incredibly funny along the way.

Beginning and ending sections include jokes about logic and logicians that teach a huge amount about logic itself. A section in the back teaches about Godel's Theorem in a simple way anyone can understand (perhaps more elegantly than Hoftadter did, perhaps not). He gives a feeling for what logic is and why we understand it the way we do.

But back to the main thing: the puzzles. First, not all are Knights/Knaves. He has some (slightly silly) puzzles of other varieties (such as the title puzzle: what

The Knights and Knaves puzzles are followed by other truth/not-truth variants. In increasing difficulty we get people who can lie or not, people who are insane and think true is false and false is true, people whose tendency to lie changes by the day of the week (which is something always unknown, of course) and take side trips into caskets with truth or lies on them and other variants.

The important piece there is "in increasing difficulty." This book is a disguised master course in boolean logic. Repeatedly, a puzzle will step back and ask you to solve a general case, without knowing exactly what situation it will be applied to.

By the end of the main puzzle section, we come to the actual Riddle of Dracula, which presents the problem of writing one solution that works for every puzzle up until then, across several chapters of the book. Smullyan isn't teaching how to solve a puzzle, he's teaching how the

In the later chapters he discusses this openly and (lightly) applies the same principles to other varieties of puzzles, whch leads into his discussion of Goedel. That turns this book into a class not just on Boolean logic, but on the learning and the synthesis that form the basis of all science.

And it's incredibly funny along the way.

May 17, 2012

A really excellent set of puzzles, for which I have only minor complaints: first, they tend to be easy, medium, or impossible. (I don't particularly enjoy the open-ended ones, like "what would you say." But I think it's just a time thing--if I can solve the problem in 2-5 minutes, that's just fun. If I have to put in REAL time, then I feel like I should be doing some actual work.) Also, the set of puzzles involving insane vs. sane, liars vs. truth-tellers I could never wrap my mind around. It's too hard to figure out when the insane people don't have any consistency to their beliefs. Like, how can someone believe they are a human but not believe that they believe they're human. Anyway, this section is probably logically valid, but posing it as "belief" makes it extremely difficult.

Mad props for doing a set of puzzles built around the Incompleteness Theorem, though. That section is fantastic.

I would love to find a way to use this book as a text for an intro to logic. It's a fantastic introduction (in puzzle form!) to logical argument, conjunction and disjunction, implication, proof by contradiction, negation, etc.

Mad props for doing a set of puzzles built around the Incompleteness Theorem, though. That section is fantastic.

I would love to find a way to use this book as a text for an intro to logic. It's a fantastic introduction (in puzzle form!) to logical argument, conjunction and disjunction, implication, proof by contradiction, negation, etc.

December 10, 2014

Modi d'uso:

1 - Aprire il libro

2 - Risolvere gli enigmi

3 - Chiudere il libro al primo segnale di noia o nervosismo

Ripetere i passaggi 1, 2, e 3 a giorni alterni. Meglio se dispari.

1 - Aprire il libro

2 - Risolvere gli enigmi

3 - Chiudere il libro al primo segnale di noia o nervosismo

Ripetere i passaggi 1, 2, e 3 a giorni alterni. Meglio se dispari.

September 24, 2021

A primera vista es un libro de pasatiempos, puzzles matemáticos y en general entretenimiento inteligente. Pero es algo más. Sí, hay acertijos de lógica y hay pasajes divertidos. Pero hay aún algo más. A medida que vamos resolviendo problemas que nos plantean vampiros que solo dicen la verdad, o que solo mienten, o que pueden hacer una cosa u otra, vamos apreciando el mensaje de fondo que nos transmite el autor, sobre la Lógica como fundamento de las Matemáticas. Es un libro de filosofía de las matemáticas disfrazado de vampiro que siempre miente o siempre dice la verdad. Es una lectura nada ligera, que requiere sentarse con lápiz y papel para sacar algunos de los acertijos (otros ni con eso), y estar dispuesto a echarle unas pensadas. No es un entretenimiento ligero. Es un aprendizaje con entretenimiento. Otros, sin embargo (y hay muchas decenas) só son divertidos y sencillos. El libro tiene suficiente para todo tipo de públicos.

De los primeros problemas:

De los primeros problemas:

My introduction to logic was at the age of six. It happened this way: On April 1, 1925, 1 was sick in bed with grippe, or flu, or something. In the morning my brother Emile (ten years my senior) came into my bedroom and said: "Well, Raymond, today is April Fool's Day, and I will fool you as you have never been fooled before!" I waited all day long for him to fool me, but he didn't. Late that night, my mother asked me, "Why don't you go to sleep?" I replied, "I'm waiting for Emile to fool me." My mother turned to Emile and said, "Emile, will you please fool the child!" Emile then turned to me, and the following dialogue ensued:

Emile: So, you expected me to fool you, didn't you?

Raymond: Yes.

Emile: But I didn't, did I?

Raymond: No.

Emile: But you expected me to, didn't you?

Raymond: Yes.

Emile: So I fooled you, didn't I!

Well, I recall lying in bed long after the lights were turned out wondering whether or not I had really been fooled. On the one hand, if I wasn't fooled, then I did not get what I expected, hence I was fooled. (This was Emile's argument.) But with equal reason it can be said that if I was fooled, then I did get what I expected, so then, in what sense was I fooled. So, was I fooled or wasn't I?

I shall not answer this puzzle now; we shall return to it in one form or another several times in the course of this book. It embodies a subtle principle which shall be one of our major themes.

January 22, 2021

This classic recreational mathematics title, based on logic problems dates back to 1978, though it feels as if it might have been written forty years earlier from the type of humour it features, a feeling enhanced by the publisher's decision to reprint it by scanning an old edition, rather than resetting it.

There is some excellent material in here, some familiar, others still with a novel edge today. There are some basic challenges - for example we're looking at a picture and told 'Brothers and sisters have I none, but this man's son is my father's son' and asked whose picture it is, plus some catch-you-out puzzles such as asking in which country you'd bury the survivors of a plane that crashes right on the border of the US and Canada. But the meat and drink of the book is a whole slew of puzzles where we are required to deduce something from a set of logical statements.

Many of these puzzles are based on variants of a situation where there are two different kinds of people, one type who who always lies and the other type who always tells the truth (sometimes there is a third kind who might do either). These problems come in all sorts of variants featuring knights and knaves, Dracula, zombies and more, but the basic principles are aways the same, though the combinations become more and more convoluted. There are also a very similar feeling set of puzzles where a number of statements are put against each other, such as caskets with labels on that indicate between them where treasure is located. And we also get some consideration of the extremes where logical statements become meaningless, such as 'This statement is false.'

The truth/lie problems take up significantly more than half of the book, and after the first few I did find these too much like work rather than fun and couldn't be bothered to work them out. The fun in mathematical puzzles and diversions comes from novelty - when you are presented with one problem after another that is just a variant on the previous one, it becomes hard to retain much enthusiasm.

There were also some examples of logic problems that suffer very badly from the 'only one solution' fallacy, which can be a failing in mathematicians. One that's in the book involves a person who every day leaves his flat on (say) the 25th floor and every evening comes home but gets out on (say) the 23rd floor. Why? Raymond Smullyan gives us the traditional 'right' answer - but I've used this as an exercise in creativity sessions and had more than 20 right different, equally valid, right answers proposed. This is the difference between problems set in the real world and those in a mathematical world where you can have someone who 'always lies'.

There's also something of an oddity in that Smullyan repeatedly asks us through the book 'What is the name of this book?' I was expecting some kind of clever-clever response like 'What' (because 'What' is the name of this book), although the question mark at the end of the title rather precludes it being a statement. But Smullyan responds 'Well, the name of the book is "What is the Name of This Book?". Since that is what's printed on both the cover and the spine, it's hard to be surprised. I can only guess that, since the illustration has most of the title ripped off, that the original version didn't also have the full title printed on it. Otherwise it's a very limp ending.

Overall, there's some excellent material here, but if you stripped out the dated humour and the repetition of variants on the same problem, what's left is probably not much more than a long magazine article.

There is some excellent material in here, some familiar, others still with a novel edge today. There are some basic challenges - for example we're looking at a picture and told 'Brothers and sisters have I none, but this man's son is my father's son' and asked whose picture it is, plus some catch-you-out puzzles such as asking in which country you'd bury the survivors of a plane that crashes right on the border of the US and Canada. But the meat and drink of the book is a whole slew of puzzles where we are required to deduce something from a set of logical statements.

Many of these puzzles are based on variants of a situation where there are two different kinds of people, one type who who always lies and the other type who always tells the truth (sometimes there is a third kind who might do either). These problems come in all sorts of variants featuring knights and knaves, Dracula, zombies and more, but the basic principles are aways the same, though the combinations become more and more convoluted. There are also a very similar feeling set of puzzles where a number of statements are put against each other, such as caskets with labels on that indicate between them where treasure is located. And we also get some consideration of the extremes where logical statements become meaningless, such as 'This statement is false.'

The truth/lie problems take up significantly more than half of the book, and after the first few I did find these too much like work rather than fun and couldn't be bothered to work them out. The fun in mathematical puzzles and diversions comes from novelty - when you are presented with one problem after another that is just a variant on the previous one, it becomes hard to retain much enthusiasm.

There were also some examples of logic problems that suffer very badly from the 'only one solution' fallacy, which can be a failing in mathematicians. One that's in the book involves a person who every day leaves his flat on (say) the 25th floor and every evening comes home but gets out on (say) the 23rd floor. Why? Raymond Smullyan gives us the traditional 'right' answer - but I've used this as an exercise in creativity sessions and had more than 20 right different, equally valid, right answers proposed. This is the difference between problems set in the real world and those in a mathematical world where you can have someone who 'always lies'.

There's also something of an oddity in that Smullyan repeatedly asks us through the book 'What is the name of this book?' I was expecting some kind of clever-clever response like 'What' (because 'What' is the name of this book), although the question mark at the end of the title rather precludes it being a statement. But Smullyan responds 'Well, the name of the book is "What is the Name of This Book?". Since that is what's printed on both the cover and the spine, it's hard to be surprised. I can only guess that, since the illustration has most of the title ripped off, that the original version didn't also have the full title printed on it. Otherwise it's a very limp ending.

Overall, there's some excellent material here, but if you stripped out the dated humour and the repetition of variants on the same problem, what's left is probably not much more than a long magazine article.

This was such a fun book! A lot of the games were similar (knights & knaves) but since I went through this book really slowly I still enjoyed all of them. I really liked that each chapter had a story that connected all the problems together. Also, you can really tell that the author loves logic and had a lot of fun while writing this.

September 20, 2020

A great and humorous puzzle book. It has left me questioning my notion of truth. My only complaint is that a few of the puzzles boiled down to checking a lot of cases. The vast majority of puzzles were very clever though, and it was only in the final chapter that they became too difficult for me to solve. All in all this book was a great pleasure to go through.

October 6, 2014

Konečně jsem před 14 dny v antikvariátu sehnal knížku "Jak se jmenuje tahle knížka", kterou asi mnozí znáte. Pro mě to byla novinka.

Sháněl jsem ji sice pro dcerku, protože po mně pořád chtěla nějaké hádanky a mně docházely nápady, ale sám jsem knihu teď po večerech zhltnul, a musím řict, že tuto knížku jsme měl fakt číst někdy v 11, kdy bych byl asi okouzlen třeba "triky" s implikací na ostrově poctivců a lhářů, nebo ohromen mocí ekvivalence, která je silnější než moc pomateného upíra Draculy. A nedokázal bych jako dítě určitě vše vyřešit jen "z hlavy".

Kniha je skvěle napsaná, hádanky jsou zábavné, výrokovou logiku si alespoň trochu inteligentní dítě osvojí tak rychle, že ani nepozná, že se něco učilo, a jako bonus je v poslední kapitole solidní a přístupný výklad Gödelovy věty o neúplnosti. Takto by asi měl vypadat výklad logiky na ZŠ/na gymplu.

Sháněl jsem ji sice pro dcerku, protože po mně pořád chtěla nějaké hádanky a mně docházely nápady, ale sám jsem knihu teď po večerech zhltnul, a musím řict, že tuto knížku jsme měl fakt číst někdy v 11, kdy bych byl asi okouzlen třeba "triky" s implikací na ostrově poctivců a lhářů, nebo ohromen mocí ekvivalence, která je silnější než moc pomateného upíra Draculy. A nedokázal bych jako dítě určitě vše vyřešit jen "z hlavy".

Kniha je skvěle napsaná, hádanky jsou zábavné, výrokovou logiku si alespoň trochu inteligentní dítě osvojí tak rychle, že ani nepozná, že se něco učilo, a jako bonus je v poslední kapitole solidní a přístupný výklad Gödelovy věty o neúplnosti. Takto by asi měl vypadat výklad logiky na ZŠ/na gymplu.

December 30, 2015

I got this book after reading The Tao Is Silent and deciding that Mr. Raymond Smullyan must be one of my favourite people out there. A logician, a magician, a pianist, a Taoist

Most puzzles in the book were based on similar themes and got a bit repetitive after a while, but really, how creative can you get with just logic, 0s and 1s that is? At this point it has to be said that lately I've been more interested in "irrational" puzzles, ones that have to be solved by acuteness of observation or thinking outside the box rather than clear-cut logic, i.e. those that try to trick you into blindly and thoughtlessly following logic, when using logic alone for solving the puzzle ends up being a hindrance, not a tool. I'm talking about games such as the ones Alberto from Spain taught me and I now play with groups of people whenever I get the chance.

Still, there's plenty in

I'm making it my gift to dad this New Year's; let's see if he's going to like it at all, him being more of a rational thinker than me and all. Maybe he can use these stories in his English classes in some way as well.

Solution to puzzle at top of review:

Fascinating book for all of us that love a good logic challenge.

Great book, nicely written and with that bit of humor that everyone could enjoy.

This is a nice book, one oldie but still a good reading.

Great book, nicely written and with that bit of humor that everyone could enjoy.

This is a nice book, one oldie but still a good reading.

February 13, 2019

If you're a die hard fan of logical puzzles or if you want to gain the knowledge in that area, only and only then, this is the book for you. The puzzles get harder and harder at each step... Sometimes you might get frustrated for taking up the same things from a bit variation, or the monotomy of the scenes, but still, a great collection of variations of Knights and Knaves and Portia's Caskets' puzzles.

A couple of things I noticed which would really help:

1. Try to take it up with a clear mind. Apart from the couple of initial chapters (that too only if you have a basic knowledge of logic), the puzzles are not something you'd be able to do while otherwise occupied.

2. A little at a time would be much fruitful. If you have extra time in your day, take up another book on the side.

3. Try not to get to the solutions immediately. If you can't figure out the solution in your mind, take a pen and paper, but avoid solutions as much as you can.

4. Even if you get the solution right, try to read the explanation given in the solution part. It helps to a great extent. Also, at some parts, you get to know that your solution was a mere guess, and the process given there is correct to arrive at it.

A couple of things I noticed which would really help:

1. Try to take it up with a clear mind. Apart from the couple of initial chapters (that too only if you have a basic knowledge of logic), the puzzles are not something you'd be able to do while otherwise occupied.

2. A little at a time would be much fruitful. If you have extra time in your day, take up another book on the side.

3. Try not to get to the solutions immediately. If you can't figure out the solution in your mind, take a pen and paper, but avoid solutions as much as you can.

4. Even if you get the solution right, try to read the explanation given in the solution part. It helps to a great extent. Also, at some parts, you get to know that your solution was a mere guess, and the process given there is correct to arrive at it.

June 17, 2022

This is what I would call a Good Ferry book. Before I retired, a ferry trip was part of my commute, and this would have been perfect -- a book you can pick up and peruse at any point that lets you forget your commuting. It's chocked full of nearly 300 logic puzzles, ranging from clever to tiresome (many on the theme of the lying whitefoot and truthful blackfoot, which become mind-numbing.) Also includes a few logic puns and jokes, as well as some old favorites like "which side of the border do you bury plane crash survivors?" Author has a sense of humor about the whole subject. Oh, and the title is a little misleading in that it really has nothing to do with books in general.

June 27, 2017

This was an entertaining collection of puzzles, with some logic being explicitly taught along the way.

The final Part was generally very different in tone from the rest, and the description of Gödel's actual work could have done with more unpacking, I feel. So if you're after intuitive understanding of those theorems, I could not recommend this as a sole source.

Also worth noting: the book certainly shows its age with the exoticism and implied casual sexism.

The final Part was generally very different in tone from the rest, and the description of Gödel's actual work could have done with more unpacking, I feel. So if you're after intuitive understanding of those theorems, I could not recommend this as a sole source.

Also worth noting: the book certainly shows its age with the exoticism and implied casual sexism.

April 2, 2021

*** read for my math class ***

Super fun puzzles and smullyan is by far one of the most interesting people I have ever researched. If you want to stimulate your brain for any kind of task (after failing to focus, feeling jittery, etc) do some of these (or just think about them) and everything will become easier.

Super fun puzzles and smullyan is by far one of the most interesting people I have ever researched. If you want to stimulate your brain for any kind of task (after failing to focus, feeling jittery, etc) do some of these (or just think about them) and everything will become easier.

June 6, 2021

Very accesible book about logic, with lots of brain teasers and sentences like “this sentence is false” (and some Gödel at the end). There probably is no easier way to explain the philosophic topic of logic. However, logic is hard and I probably did not invest enough work that this book merits. So perhaps the three stars more reflect my own shortcomings than the book’s.

January 26, 2022

A fun book that presents one logical riddle after another, and teaches some basic tenets of logic along the way. I had fun teasing out several of these puzzles, and I hope to share some with my high school students as the semester rocks on.

November 10, 2022

Kapitoly su pisane zabavnou formou a ak sa prehryziete dostatocne daleko, narazite aj na vtipy a anekdoty. :)

Musim sa ale priznat, ze po case sa mi uz priklady prestalo chciet lustit a ked som sa ku knihe opat vratila, nevedela som sa uz tak lahko posuvat dopredu.

Musim sa ale priznat, ze po case sa mi uz priklady prestalo chciet lustit a ked som sa ku knihe opat vratila, nevedela som sa uz tak lahko posuvat dopredu.

May 8, 2017

This 1978 book about logic and logic puzzles made my brain work! But this book is funny too and lighthearted. And the solutions are in words not formulas or truth tables.

July 13, 2017

Lots of good puzzles, but a bit repetitive. I don't need 20 knights & knaves problems.

April 27, 2018

First brush with Gödel's incompleteness theorem. Wasn't expecting that from a recreational puzzle book.

February 13, 2019

Te tienen que gustar mucho los juegos de lógica para que no se te haga pesado.

Fun, but feels like brunch table puzzle game book

April 20, 2021

A fantastic, fun and approachable book about logic puzzles and understanding the reasoning behind them

Acquired Aug 9, 1999

Brown Bag Bookshop, Rochester NY

Brown Bag Bookshop, Rochester NY

November 5, 2022

Tato knížka je jedním z důvodů, proč jsem se vydala na studium matematiky. Teď mi ji připomněl M. du Sautoy, tak si ji sem jen doplňuji a doporučuji jako dětskou knihu pro zvídavé mladé čtenáře.

February 5, 2023

From Wittgenstein to Göddel's theorem in a series of funny logical riddles. I like his approach to teach :D

November 14, 2014

Raymond Smullyan is - IMO - the most fun and creative logician who ever existed. I have always loved his books and this is no exception. It is one of his earlier ones and has a great mix of logic problems (Knights who tell the truth, Knaves who lie - sane and insane humans and vampires) as well as some talk about paradox and it concludes with his trying to make Godel's incompleteness theorem accessible to non-mathematicians.

Okay - for that last part he failed since I still don't understand it. And there were a few sections about the "what do you believe you believe"? that were too hard for me to follow. But the majority of puzzles are fun and interesting.

You will find many Brain teaser books but Smullyan's are the only ones I feel a real workout with BUT feel I can still do them. Some brain teaser books have puzzles that are so hard only a devout mathematician could solve them, some have puzzles that are fun but rely on twists. These are the only ones I have found that rely not on math or getting a twist but good old logic and thinking. Doable by anyone, but still enough of a challenge you feel smarter for having done them.

I love Smullyan. He is one of those "wish I could have met him" people who touched my lives through their works.

Okay - for that last part he failed since I still don't understand it. And there were a few sections about the "what do you believe you believe"? that were too hard for me to follow. But the majority of puzzles are fun and interesting.

You will find many Brain teaser books but Smullyan's are the only ones I feel a real workout with BUT feel I can still do them. Some brain teaser books have puzzles that are so hard only a devout mathematician could solve them, some have puzzles that are fun but rely on twists. These are the only ones I have found that rely not on math or getting a twist but good old logic and thinking. Doable by anyone, but still enough of a challenge you feel smarter for having done them.

I love Smullyan. He is one of those "wish I could have met him" people who touched my lives through their works.

April 20, 2017

El deixo uns dies, m'atabala massa…

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