Popper -- Science versus non-science: Conjecture and refutation.


Popper is one of the philosophers of science who has had the biggest impact on the practice of science.


In this paper Popper is asking two related questions:

1)      How do we determine whether or not a theory is scientific? (This does not refer to importance or truth or meaningfulness or acceptability.)

2)      What is the scientific method?


Pre Popper; Inductive Scientific Method


Step One: Make Observations

These observations are the premises in an inductive argument the conclusion of which is:

Step Two: Make Theory/Hypothesis

Step Three: Test Theory

            You do this by making more observations.




Here is a black crow.

The crows around Catt Hall are black.

The crows around the Union are black.

The crows around the gates of hell are black.

All crows are black.                                          ß This is my theory.


How do I test the theory? I go to the Bahamas and see if the crows are black there.


Problems with this method:

1)      Psychological.  It is very easy to find evidence to confirm something that you already believe and very easy to ignore evidence that conflicts with something that you already believe.

2)      Methodological. You can’t collect observations unless you already have a theory about what you are trying to observe.  Popper would argue that this crowologist had to have a theory about crows being black before she could collect the first premise.

3)      Logical.  Remember that this is an inductive argument and don’t present the conclusion as certain. 


Popper’s solution:  Falsificationism.


Scientists ought not to be trying to find evidence that confirms their theories, rather they should be trying to find evidence that conflicts with their theories.


A theory is falsifiable if you can imagine an observation that you could make that would cause you to reject the theory.




If all crows are black then the crows in Cancun should be black.

The crows in Cancun are red.

It is not the case that all crows are black.


The logical structure of this argument:

If H then O

Not O    

Not H


If the hypothesis is true than I predict observation O.

I did not/could not observe O.

Therefore the hypothesis is not true.


Note that this is a valid deductive argument.



1)      For something to count as scientific Popper thinks that we need to be able to imagine an observation that could be made that would cause us to reject the hypothesis.

a.       In order to test a hypothesis we need to try to falsify it.

b.      The less likely the observation, or in other words the riskier the prediction, the better the test of a theory.

2)      The question that we need to ask now is: “Where do hypotheses come from?” and Popper’s answer is that scientists make them up (conjecture).

a.       Popper thinks that since there is no recipe for coming up with hypotheses (they are a result of the individual creative genius of scientists) that we don’t actually start doing science until we start thinking about falsifying out hypotheses.


Be sure that you can explain how Popper’s falsificationism meets all three of the problems that he raises for an inductive scientific method.


A real example!!

Popper thinks that his falsificationism is what distinguishes science from non science, and he uses the examples of the marxist theory of history, psychoanalysis, and Einstein and the Eddington experiment to show this.


He thought that Einstein’s theory of gravity was the only one that was really science because it was the only one that was falsifiable.  Here is how the example goes:




Eddington thought up a great experiment that would allow us to make this very observation.



With the other theories, it is impossible to describe a behavior that is not consistent with them.  It is impossible to make a risky prediction.


Popper thinks that the way to test whether or not a theory is scientific is to ask yourself, “what would it take to make this theory false?”  If the answer is nothing, it isn’t science.



“The criterion of the scientific status of a theory is its falsifiability, or refutability, or testability.”


The other three theories are untestable, but for different reasons:


This is the problem of demarcation. Drawing a line between science and other ways of knowing.  The criterion of falsification is the solution to this problem.