The candle problem

In an empty room are a candle, some matches, and a box of thumbtacks. The goal is to have the lit candle about five feet off the ground. You’ve tried melting some of the wax on the bottom of the candle and sticking it to the wall, but that wasn’t effective. How can you get the lit candle to be five feet off the ground without you having to hold it there?

This problem was introduced by Karl Duncker in 1945 as a cognitive performance test, and was used by Daniel T. Willingham in his article “Why Don’t Students Like School? Because the Mind Is Not Designed for Thinking” as an example of how critical thinking is hard. He claimed that the brain is not designed for thinking but designed to save you from having to think, because thinking is slow, effort-full, and uncertain.

In the candle problem, the solution is not tricky (check the solution here). However, if you don’t have enough background from similar problems it might take you a lot of time to come with the solution or you might give up thinking before solving the problem. He said that people mainly rely on memory rather than thinking. Most daily problems are ones we have solved before, so we just do what we’ve successfully done in the past and that’s known as experience. According to him, critical thinking is not a specific skill but it is a process tied to what we already know and stored in our Long-term memory. We relate what is in our Long-term memory to the current working memory to solve the problem.

An important concern he raised about students is that:

Working on problems that are at the right level of difficulty is rewarding, but working on problems that are too easy or too difficult is unpleasant.

If the student routinely gets work that is a bit too difficult, it’s little wonder that he doesn’t care much for school. Teachers should try to understand students’ feelings about problems they face for the first time like the teacher’s feeling when he hear the candle problem for the first time.

Finally, I want to add a conclusion from Jim Askew’s blog “Web-based instruction 4 teachers” the post with the title “Why Critical Thinking is Hard Work!“.

When teachers ask a question, they must WAIT for the answer. Students need time to process information! As students begin to understand, and practice the process, they WILL be able to process faster! 

20 thoughts on “The candle problem

  1. Silence is difficult for many people to sit with, I see that everyday in our counseling clinic where we are training new counselors. Yes, people/students need time to process things when new thoughts or ideas are proposed to them. We, as the teachers, need to gain comfort in the silence that follows. Giving the students the space to think about it and form a response challenges them. If the teachers jump in and rescue after a few moments of silence, they come to expect it and never allow themselves to rise to the occasion. Good questions should give students pause. Good teachers give their students questions and then time to think.

    1. Exactly, as a teacher you need to give time to students to think. Questions also have another benefit which is to to keep students concentrating to be ready to answer. Also, it works as a pause from continuous talking that cusses boredom to the receivers.

    2. I think that both teachers and students should gain more comfort with silence. Silence is important so long as the students are engaged. It gives them a chance to make connections with concepts they already understand.

      I disagree with the notion that we use knowledge rather than thinking. I think that we use our knowledge to think by making connections with things that we already know. We get overwhelmed when we are presented with a question that we don’t have any underlying knowledge to connect it to.

    3. Silence is definitely crucial for students to be able to stop and process what they’ve been listening to. It provides needed breaks in between sessions of talking and listening–as anyone who listens to jazz knows, the pauses are as important as the notes themselves. That being said, it’s also somewhat nerve-wracking as a teacher to sit and wait in silence for an answer; I’m left wondering if I asked too difficult a question, or if I’m waiting too long before helping them out, etc.

  2. Thanks for your post. I especially relate to the idea that we enjoy challenges at the “right” level of difficulty almost like the Three Bears! It’s so true, but how does one get to the right level especially when you have a room of 50 students?

    I also enjoyed the candle problem. Happy to say I nailed it (pun intended), but I am curious if there are other “right” answers!

    1. I think the candle problem could have many solutions. For me, I did not get the official solution. I also thought in your solution but I think this solution may not last for long time.
      In classes of 50 students for example, you could give students printed questions and ask them to work in groups of two or three for like 10 minutes. By this they will cooperate and a student in a lower level will learn indirectly from his peers.

  3. Really like that you brought the candle problem into this conversation. Often we forget that we need to challenge our students but also give them problems that they can actually solve. I remember some of my the most frustrating times during my undergrad were trying to solve a problem for a class only to find out the professor had made a mistake and it could not be solved. The candle problem is a great example of how we can find challenging problems that require a little extra thinking to really get at the right answer.

    1. Yes, I agree. Teachers/professors should think first in problems before giving them to students to ensure that they are correct (in order not to fail in the same problem as you got :)). And to see if it will be suitable for the thinking level of students. I think challenging problems also raise curiosity to learn.

  4. Thank you for your post. I agree with you that we rely on our memory more than thinking.
    I have one concern about the candle test!When I was faced with the candle problem, the first thing I thought about was: why the goal is “to have the lit candle about five feet off the ground. as the purpose of the doing it”. Is it because of avoiding fire? I thought about this instead of thinking about a solution. And then when I could not understand it I did not try to solve it. In all activities, the final aim of the activity is more important: “why we learn this”, “why we want to solve this”. Understanding the problem and objectives help to come up with innovative solutions. There is not one right way to solve most problems. I am eager to know if somebody came up with another solution for the candle problem. I am almost sure not! That is why I think the test has some important biases and I can not trust on its results.

    1. This problem was not meant to be an actual situation to deal with, at least you were able to hold the candle. The aim of this problem is to stimulate the mind to think in a situation with constraints. The problem without these constraints is a normal problem that could have many solutions and that we have faced a lot in our life so we are using our memory or experience in it. However, formulating the problem in this way was only to prove that an easy task appears difficult if you have to think from scratch not based on what you have in memory.

  5. Great post!
    I have two follow-up comments. One is regarding questioning. I for sure believe questioning is a great strategy that promotes critical thinking in our students. For me the best instructor is not only the one that provides thoughtful questions, but rather the one that promotes a learning environment where students are motivated to ask thoughtful questions. If you can create a learning environment where students are the one asking the meaningful questions and debating about the topics, the knowledge will be richer for sure. For this, we need to be able as instructors to recognize that we don’t have all the answers and that we are learning together in the classroom.

    The second point is about right or wrong answers. When we approach problems thinking that there has to be one right answer, I believe we are limiting our learning. At the end is all about the process rather than the result. If students can reflect on all the thinking process they were through in order to solve the candle problem, they can learn more about their problem-solving skills, and most importantly they will learn how to adapt their learning process to different situations and contexts. That for mi is one of the most important tasks of education the ability to transfer knowledge to different situations. If we think in terms of the only right answer, against the wrong answers, we are losing focus on the process.

    Thanks for sharing!

    1. Thanks for your valuable comments. I agree that creating a learning environment that help students to ask good questions is a great achievement. I once heard one professor saying that the aim of PhD programs is not just to make good publications but to teach students how to ask good questions.

  6. Great post! I love to ask questions when I’m conducting a lab or lecturing in classroom, and I completely agree that asking the RIGHT questions (appropriate level of difficulty) is essential to encouraging critical thinking. The big question is….what kind of questions should we ask? I’m sure it depends of the field of study. Personally, when teaching a class in horticulture, I tend to ask two types of questions in attempt to stimulate learning: 1) real-world application questions (e.g., “let’s say you are a landscape contractor in ________situation…what would you do”) and 2) “based on what you’ve learned so far, what’s your expectation?” questions. In almost all cases, I’m evaluating how they came to their conclusion (their thought process), more than the actual answer. Do you have any suggestions to further promote critical thinking through asking questions? What do you (or other instructors) do differently in your field?

    1. Thanks for your comment. What I liked is your evaluation method, you evaluate based on how you solve, and think, more than the final solution. Questions really differ by field, for example in programming it is much easier to change some part in the code and ask students How do you think this change will affect the output.

  7. You’ve got tons of wonderful comments on this, so I’ll just add to the general enthusiasm and also echo Homero’s reminder that we want students to ask the questions, and that mistakes are invaluable learning opportunities.

  8. This is a great post! You raised so many good points. I think asking good questions is so important but that designing the difficulty to where critical thinking is facilitated can be tricky! Nonetheless, an incredibly important one to address!

  9. Great points! One thing that I want to add to posing questions is balancing the amount of questions. I have been in courses where the instructor confuses the students by asking too many questions and answering a questions with another question! I think that defeats the purpose of asking questions… Since by asking questions we are teaching students to be critical thinkers and trying to guide them to the right path… However too many questions will just confuse the learns.

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