The Demarcation Problem and Falsifiability

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Area: Science
Grade Level: High School & Beyond
Topics: belief, demarcation problem, Epistemology, Philosophy of Science, Popper, science, Truth
Estimated Time Necessary: 1 hour

Lesson Plan

Scientific Reasoning
Explore and discuss attitudes towards science

One of the practical consequences of the Scientific Revolution was a suggestion that one should only believe things that are both true and justified. Eventually, there was even the proposal by mathematician William Clifford that it is morally wrong to believe things without good justification. While early thinkers suggested we need to justify all of our own beliefs, science and the world are far, far too complicated for each of us to confirm all of our beliefs. We need to have a system to help us decide.

The challenge this raises involves what to believe. Is Chemistry well founded? Astrology? How can we tell the difference between what we might call science and pseudoscience? The stakes are quite high here…think about medicine. How can you tell which pills to take to cure your illnesses?

One famous and prominent suggestion comes from Karl Popper who writes this: Popper on Falsifiability


Discussion Questions

  • Why is the Demarcation Problem important?
  • What does Karl Popper mean by falsifiability?
  • What is the difference between saying “we should only believe things which can be falsified” and saying “we should only believe things which are false?”
  • Arthur Eddington’s 1919 confirmation of Albert Einstein’s theory of evolution was held by Popper to be a perfect example of a risky claim that made a falsifiable prediction (that is it laid out the terms under which it would be shown to be false). What does this mean?
  • Popper writes “The most characteristic element in this situation seemed to me the incessant stream of confirmations, of observations which "verified" the theories in question; and this point was constantly emphasized by their adherents,” another way of saying that confirming evidence is “cheap” or “easy”. What does he mean by this?
  • Explain the difference between these two sentences on Popper’s grounds (i.e. the difference between bad science and pseudoscience): “Lightning doesn't strike the same place twice” and “Human psychology is affected by the location of Mars.”
  • Is falsifiability falsifiable?
  • Is the Demarcation Problem important? Formulate arguments for and against this position.
  • Ludwig Wittgenstein in his work, Philosophical Investigations regularly referred to the concept of language games. He argues that concepts do not need to be clearly defined to be meaningful. Are there some areas between science and pseudoscience that can never be fully decided on?
  • Darwinian evolutionary theory is the bedrock of modern biology. Is it falsifiable? If not, how is this point significant?
  • Are there times we should hold onto some beliefs that fail empirical scientific tests (How can we know whether the hypothesis is false or if the instruments failed, or something else accounts for this failure)?


This lesson plan was created for PLATO by: Stephen Miller, Oakwood Friends School, Marist College.

This work is licensed under CC BY-NC-ND 4.0

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