You are here

Liar and truth-teller riddle with step by step easy solution

Liar and truth-teller riddle step by step solution

Think methodically with common sense reasoning to solve the liar and truth-teller riddle

In liar and truth-teller riddle, to know the safe path, a traveler can ask only one question to any of a habitual liar or a truth-teller. What to ask?

Story of the liar and truth-teller

Passing through many a land, a traveler came upon a deep jungle where the path split into two and went into the depths of the jungle.

He had heard from a wise man that such a forest lay ahead. The wise man told him, “One path will lead to the warmth of a friendly village, but the other will lead you to the den of hungry tigers and sure death.”

Now only he remembered the rest of what the wise old man told him, “When you are at the fork trying to figure out the safe path, two men will suddenly appear ready to help you. Beware, one of them will be a habitual liar—his answer to any question must always be a lie, but the other will just be the reverse—he always will tell you the truth.”

The wise man finished, “Don’t forget, you can ask only one question to any of the two to find the correct safe path. You won’t get a second chance. They will understand your question, know the safe path, and know the nature of answering of each other but will answer only with YES or NO.”

Recommended time for you to find the safe path: 15 minutes.


This is a classic logic puzzle from old times. Logicians who juggle with pure logic by choice will tell you the right answer in no time. But we are not logicians. We are common folks who use common sense logic and deductive reasoning in our own way.

If you are not a logician, have a go. The experience will be enriching.

You’ll get better results if you imagine yourself as the traveler.

Systematic Solution to the Liar and truth-teller Riddle—First stage

Key Pattern Discovery of the Nature of the Answer for Choosing the safe path

Without going deep into the riddle, you will take up an initial trial in mind. You will visualize what could be the answers from the two if you ask the simple, straightforward question,

Do you think the path to my left is the safe path to the village of friendly people?

If indeed the left path IS the safe one,

The liar will answer: NO, and the Truth-teller: YES.

Without knowing which one of them is telling the truth, you won’t be able to decide.

Thinking more you realize you have,

Two unknown paths, and two men eager to help, but again you don’t know their nature of habitual answering.

With such combinations of unknowns, you understand, it will be impossible to form the right question if you think in conventional way. You realize,

You must form the question NOT in a simple way.

Without wasting time on what type of question you have to ask, your attention shifts to the ANSWER itself.

This is a natural way to solve problems—to analyze and understand all characteristics of the end result first, comparing it with given information.

Note: The method is End State Analysis Approach, an often-used natural problem solving technique packed with power.

Thinking more in this direction, you ask yourself the most important QUESTION at the moment,

What must be the NATURE OF THE ANSWER from the two for me to know the safe path?

You have already experienced that the answer to a simple question from one helper will be NO and the other, YES, just the reverse.

You make a firm conclusion,

If the answers from the two are REVERSE to each other, you won’t find the safe path.

No going away from this. The conclusion is a fact and an inviolable truth.

Ah ha, you couldn’t imagine earlier it would come to this pass. Yes, for you to be sure about the safe path,

Whatever be the question, answers from both the helpers must be the SAME in every situation.

This is a revelation to you and in problem solving terminology is discovery of the key pattern. You have now a precise requirement of their answers to the single question (or precise requirement specification).

Naturally, the answer will be YES or NO. But if it is NO, both will answer NO. Same must also be true for YES for knowing safe path.

This is the first breakthrough. You know half the battle you have won by knowing all about the answer that can be known.

Nature of answer fully identified, it is time to shift focus of attention to the NATURE OF THE QUESTION.

Systematic Solution to the Liar and truth-teller Riddle—Second stage

Process of Knowing Nature of the Question to ask

You realize you have to think in a NEW way to make the second breakthrough by understanding precisely the nature of the question—the requirement specification of the question.

What can be a new form of a question! As you think more on this, the requirement of ‘NEW form’ strikes you and aided by the focus of the new form of question you reason,

Well, the usual simple form of the question has been a single question for any combination of situation. 

All forms of such a question would have the same end result of failure.


Property change analysis technique

The technique of exploring new ways to change a key property (in this case, the number of parts in the question) of the key entity (in this case, the question itself) often produce great results for quick and innovative solution to the problem. This is called, Property change analysis.

Of course, you can very well change the number of parts in the single combined question, especially as you remember from your experience,

Instead of a single question, two questions can easily be combined to form the single compound question.

When you were younger, your neighbor uncle once asked when you opened the door,

Is your father home? Is he well?

Your father was home and well. So you answered, Yes.

One answer to two questions.

You further realize, if either your father were not home or not well or both, you might have simply said, No.

That must be the new way that will help you know the safe path,

Instead of one-part single question, you will ask a single question with two component questions joined together by AND, the easiest way to join two questions.

And you know from elementary knowledge in language that such a compound question is easy to form—your neighbor uncle could have asked such a single question,

Is your father home and well?

You think you have more or less solved the problem and that too by using no difficult technique or concept.

You have followed just simple common sense problem solving techniques coupled with concepts drawn out of everyday real life experiences and elementary knowledge of language.

What have you achieved till now?

You know now both the form of the question to ask and nature of the answer.

The only task left is to create such a question with such an answer in reality.

Systematic Solution to the Liar and truth-teller Riddle—Third stage

Forming the Question by using the Answer and Question Specifications

With clear idea of the nature of the answer and form of the question, a possible question to be asked could be,

Are you the truth-teller, and do you think the path to my left is the safe path?

Possible scenarios are,

Situation 1: The helper asked is the truth-teller and the left path is the safe path: Final answer: YES.

Situation 2: The helper asked is the liar and the left path is the safe path; his answer to first part of the question will be NO. So answer to the combined question will truly be NO. Habitual liar, being what he is, cannot but reverse this NO to YES. His final answer will be YES.

So if the answer to your question is YES till now, you may assume that the left path is the safe path.

Rest of the possible results when the left path is not the safe path are,

Situation 3: The helper asked is the truth-teller and the left path is NOT the safe path: Final answer: NO.

Situation 4: The helper asked is the liar and the left path is NOT the safe path. Correct answer to both the first and second parts of the question being NO, the habitual liar will reverse it to YES. Final answer: YES.

The answer differs from the answer by the other helper. It violates the requirement specification of the answer.

Just on the brink of success, you find that joining of two questions simply by ‘and’ won’t fully work.

There is a challenge yet to overcome at the third stage of using the specifications of the answer and question to form the right way to combine the two question parts. You assumed an easy way to join the two questions without thinking much on how to join.

But the effort is not all in vain—you will get important clues on how to combine by analyzing the results of the trial.

Systematic Solution to the Liar and truth-teller Riddle—Final stage: Identifying Crucial Requirement of Joining two Questions

You wonder, why and where did combining two questions by ‘and’ fail?

As you concentrate on finding answer to this question by analyzing the result of your last try, you realize,

  1. Answers to the component question 1 and question 2 are independent of each other, and
  2. No need to think about the answer of the truth-teller, because primarily the goal is to force the liar to reverse the answer of the truth-teller twice to match his final answer. Liar is the most important person in the solution.

In the Situation 2, using ‘and’ for joining, you could indeed force the liar to reverse the answer of the truth-teller twice.

But in the Situation 4, where true answer to both part of questions were NO, the liar reversed each to YES and combined also to YES. HE was happy to think that he had indeed reversed the true combined answer and did justice to his habit!

It leads you to discover the breakthrough idea. To force the liar to reverse true answer twice by two questions,

One question must be DEPENDENT on the other.

So, the successful method of joining the two questions must make sure that,

The liar will reverse correct answer to the INDEPENDENT first question. Thinking that he has answered true to his habit, he will face the second DEPENDENT question. As a habitual liar, he will now have no other choice than to reverse answer to the first independent question once more by the second question. By two reversals, answers will be correct and same as the truth-teller.

What is the other method of joining two questions that will achieve this result?

Again, your common experience of using the language helps you for the final breakthrough.

There must be only one real question but asked twice in the commonly used form,

What will be your answer if I ask you whether the QUESTION is true?

The first of the two component questions the liar must answer by the rules of the language is,

‘whether the QUESTION is true’.

The liar REVERSES the correct answer to this first component question and forms the INTERMEDIATE RESULT in line with his nature of answering.

Now he faces the second component question,

What will be your answer if INTERMEDIATE RESULT is true?

He will have no other choice than to reverse the intermediate result true to his nature and form the final result. The final result becomes the REVERSE OF INTERMEDIATE RESULT.

As INTERMEDIATE RESULT has itself been reversed once from correct result, the final result returns to the value of the correct result again by this second reversal.

Following is the schematic of this mechanism,

liar and truth-teller riddle - double reversal schematic

This is pure logic, but with reason, method and two trials, you have learned enough on how the single compound question must be formed and asked to any of the two helpers to find the safe path.

With confidence, you finally form the two-part single question that will lead you to know the safe path,

What will be your answer if I ask you whether the path to my left is the safe path?

You ask this question to any of the two helpers. If the answer is YES, you take the left path, and if it is NO, you take the right path.

There cannot be any other possibility—you have indeed forced the liar to reverse the true answer twice to match the final answer of the truth-teller in both the cases.

Knowing that answer to the question from both helpers will be same, you asked the question to any of the two helpers.


Without going into the second trial, you might have discovered the most important PRIMARY REQUIREMENT OF ACTION—the liar must be forced to reverse the true result twice.

This discovery is not difficult to make if you realize early that solving the riddle depends only on finding the right answer to the question,

How to make the liar answer same as the truth-teller in any situation!

The problem solving techniques, concepts and common knowledge used

  1. End state analysis: Analyzing the desired result or last action first. Goal is to gain more knowledge about the last action for achieving the desired result.
  2. Refining requirement specification in steps: Knowing precise requirements of the answer first and the question second simplified the steps to the solution greatly.
  3. Question, analysis and answer or QAA technique: The problem is simplified stage by stage by asking a series of relevant questions, analyzing problem details for getting the answer and actually forming the answer.
  4. Property change analysis technique: Exploring how many ways the key property of the key entity can be changed and assessing promise of each change often proves to be crucial in solving a complex problem. Great innovation can be created by this technique.
  5. Elementary knowledge in language: Basic domain concepts on combining two component questions to a single compound question, but in different ways.
  6. Well-formed trials or experiments: To learn more of the problem to identify patterns and create methods.
  7. Step by step deductive reasoning: By using all the above and discovering key patterns of information for solving the problem with complete confidence.

End note

Our focus all through the above solution process has been to think as the traveler in a simple way and find the safe path step by step using systematic reasoning and problem solving techniques drawn out of common knowledge and experience.

Know how to solve difficult problems easily without wasting time on random attempts

Our ebook on puzzle solutions by innovative methods will show you just that.

Puzzles for Adults eBook

Puzzles for Adults: 50 Brain Teasers with Step-by-Step Solutions: Boost Your Power of Problem Solving

(BUY from Apple books, Barnes & Noble, Rokuten Kobo, Vivlio, Angus & Robertson, Tolino, PayHip and others)

BUY the eBook Amazon Kindle version here, from Google Play here and Paperback here.

Second book on Innovative Solutions to Matchstick Puzzles from Suresolv

Matchstick puzzles innovative solutions

BUY Creative Matchstick Puzzles Innovative Solutions eBook Amazon Kindle version

BUY the paperback here.


Puzzles you may enjoy

Easy to hard brain teasers with systematic solutions

Challenging brain teasers with solutions: Long list.

This will always be the most up-to-date full list with the brain teasers classified into categories that can be browsed separately.

You may also click on the category term link below to enjoy the brain teasers that are classified in the present category.

For example, if the category term link shown below is "Riddle", click on it to go through all the Riddles.