A Bad Analogy is Like, Whatever.

An elderly man storms into his doctor’s office steaming mad.

“Doc, my new 22-year-old wife is expecting a baby. You performed my vasectomy 30 years ago, and I’m very upset right now.”

“Let me tell you a story,” the doctor calmly replies.

“A hunter once accidentally left the house with an umbrella instead of his rifle. Out of nowhere, a bear surprised him in the woods… so the hunter grabbed the umbrella, fired, and killed the bear.”

“Impossible, ” the old man says. “Someone else must have shot that bear.”

“You got it,” the doctor replies.

Besides just being great for a punchline, a good analogy is like a five-in-one painter’s tool. And to define what constitutes a “good” analogy, I think the previous statement is a perfect example. I know what a five-in-one painter’s tool is. My dad is a general contractor, and I spent many summers with him scraping layers of paint off of faded walls, prying open containers, squeezing paint and water off of rollers, and slathering compound on walls and floors. If you know what a five-in-one tool is, you know that “a good analogy is like a five-in-one painter’s tool” is a pretty fitting analogy. However, if you’re the type who fears the towering aisles of Home Depot, you might not relate to that analogy. And that’s something to think about when forming analogies to elucidate a concept. Perhaps those who shy away from home improvement and enjoy modern conveniences like duct tape and WD-40 could concede that a good analogy is like a George Forman Grill. In this case, the analogy is altered to appeal to a different audience.

Teachers and scientists need good analogies. For example, if I told you that semiconductors absorb light, which excites electrons and creates charge carriers, you would be well-prepared to regurgitate that information to anyone else. You would have a great grasp on some fancy scientific lingo, but you wouldn’t really know anything except some cool buzz words. This was the issue that my co-instructor and I faced while teaching the School for Scientific Thought. With undergraduates, we could make assumptions based on pre-requisites. But with this group of high school students, we had no idea whether a student was taking college-prep chemistry or had never even cracked open a physical science textbook.

This is what we did: there were about 15 students and 15 chairs surrounding a table. The entire room could be analogous to the type of material we wanted them to learn about; a semiconductor. Then, we threw a ball on the table. The ball acted in place of a photon, which is a small amount of light energy. If any student (who were all playing the role of electrons) grabbed a ball, they took the ball’s (or photon’s) energy. That means they could get out of their seat and move freely. Electrons that haven’t absorbed energy are in their ground state; they’re like students stuck in their seats. When an electron absorbs energy, it can move freely just like a student who isn’t confined to his seat.

Anyone can remember scientific terms like exothermic and endothermic, but if there’s nothing real to relate these terms to, then nothing is truly learned. Analogies give a chance for individuals to develop inquiry skills. By making a comparison, teachers can shape the way students make connections and can encourage critical thinking. In science education, good analogies promote a good physical intuition. Sometimes though, as another example of what defines a “good” analogy, analogies can be lacking.

In my own example, there is a glaring issue. When a student picks up a ball, which was supposed to represent absorbing some light energy, the student still has the ball. Many students asked, “Where does the ball go?” In reality, the light doesn’t hang around the electron. This is a tenet of physics: conservation of energy. When the students acting as electrons stand up, that requires energy. The ball is supposed to represent what gives them that energy, but it never disappears. Sometimes, holes in the analogy can get students caught up, and they lose track of relevant concepts. So not only is it important to know your audience (should I compare analogies to tools or to college dorm essentials?), it is also imperative that the analogy is fluid with any pedagogical platform that it has been built upon.

To hammer the point and to make this post a little more didactic, here are a couple of other scientific analogies, and I can try to go into a little detail on how effective they are.

Polymers are like spaghetti.

The long, extended molecules that make up what we call plastics can be described like spaghetti. Some polymers are like spaghetti with olive oil on it, where the polymer strands can slide past on another and stretch and flow (like Silly Putty). Other polymers are like old cooked spaghetti, dry and tangled so that each strand can’t really slide around. This would be more like Tupperware, which can still bend but is also pretty rigid. This analogy is fairly effective and can hit a wide audience. However, it isn’t very deep. There are lots of other descriptions for polymers that spaghetti just can’t quite cover.

Electricity is like flowing water.

The hydraulic analogy for electricity is ancient. Even the great pioneer of electromagnetism, James Clerk Maxwell, related electricity to the flow of a fluid (although he, being so cognizant in physics, chose the flow of heat to relate electricity). This analogy matches extremely well; volume can be related to charge; water pressure is related to potential; and current and water flow rate match up really well. Of course, simplifications like this are often deficient, and this analogy doesn’t hold up when considering how water pipes can leak or how flowing electrons can affect other flowing electrons far away.

Analogies can be powerful tools, but they should be used with caution. Don’t tell an audience in the UK that a good analogy is like a wrench. (You’ll need to use the word “spanner” here.) And avoid ostracizing your audience by giving an incomplete analogy (like how researchers explained that photosynthesis is like baking a cake, except that cake baking has no chlorophyll equivalent). Build up your analogies and you’ll help students understand, but you can also give them the capacity to think creatively in the future.


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