Is one of your course goals to help students discern ‘fake news’ from the real thing when running around the Inter-webs?  Do you want your students to learn the habit of being an informed skeptic when encountering documentary-style cable television shows about alien abduction, killer bees, and ancient monuments constructed on Mars?  For most faculty, helping students to develop critical thinking skills is an implicit, if not explicit, learning goal.  But, just how can a conscientious teacher make such a goal a reality in the classroom?

One thing that education research consistently confirms is that if students are to learn and master a challenging skill— such as the habit of being an informed skeptic—students need multiple opportunities to practice.  And, that practice needs purposeful feedback in order to become part of a long-standing habit of mind.

An innovative approach to helping students learn to successfully become an informed skeptic in the scientific domain is to periodically propose preposterous propositions to students.  Upon being challenged with a preposterous proposition, my students’ response tasks are three-fold.  First, and perhaps most important, is for students to identify precisely what evidence or data they need to see agree with or disagree with the preposterous propositions.  Maybe that’s a table of data from the back of the textbook.  Maybe it’s evidence that would need to be constructed from desperate data sources.  Maybe it is just a single counter-factual.  There are a lot of possibilities for students to mull over.

The second, and probably a little less important, is to use that evidence or data to disagree with the preposterous proposition.  The reason I suggest that this second step is likely less important is because students learn relatively quickly over a few assignments that my preposterous propositions are almost always incorrect.

The third step, which typically takes just a few moments, is to reword the originally proposed preposterous proposition with an accurate, but still attention grabbing, short, replacement proposition.  In the spirit of the Twitter-sphere, my requirement is that this corrected proposition be less than 140-characters, although I prefer that phrases sound like catchy-news headlines or, in contemporary student-speak, “click bait.”

Preposterous propositions are surprisingly easy to generate.  I start with the ten most common scientific misconceptions that my students struggle with, and turn those misconception ideas into news-headline-style phrases.  Here are some examples I have been working on in the domain of astronomy:

Figure 1 – Task: What Specific Evidence Do You Need to Prove These Tweets are Fake News?

  1. The brightest stars have the longest names
  2. The time it takes a star to rise and set is the same as it takes the Sun
  3. The full moon is eclipsed by Earth’s shadow every month
  4. Planets spin faster if they orbit farther from the Sun
  5. The largest planet, Jupiter, has the most moons
  6. Circling Jovian planets, the most massive moons have the smallest orbits
  7. The most massive planets are closest to the Sun
  8. Comets revealed to be frozen asteroids
  9. Sun’s temperature decreases the farther one is from its surface
  10. Nearby stars appear brighter than more distant stars
  11. Largest stars have the longest lifetimes because of larger fuel reserves
  12. Supernovas are a million times brighter than regular novas
  13. The oldest galaxies eventually develop spiral arms as their stars age
  14. Starlight takes longer to pass through the Milky Way Galaxy than the Andromeda Galaxy

Another place to get preposterous propositions is from last year’s final exam.  Simply find the most commonly missed questions—especially easy if you use multiple choice exam questions—and use the most commonly selected wrong answer choice.  Eventually, you might even get your students to bring you suggested preposterous propositions for use in future classes.

The stated goal here is to provide students with multiple-opportunities to practice looking for fake news and developing a skeptical habit of mind; however, the subversive goal here is to help students learn the scientific concepts you are teaching in your course and to combat those tenacious misconceptions that far too many students bring to your class and, as it turns out, often leave your class still clinging too.

Tim Slater, University of Wyoming,

Suggested Citation: Slater, T. F. (2017, Aug). Proposing preposterous propositions for improving pedagogy.  Society of College Science Teachers Blog, 3(1),


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