Criterion of Falsifiability: Rule
propounded by Karl Popper to the effect that the distinction between
scientific and non-scientific theories is that the scientific ones can
be falsified by their logical consequences.
The criterion of
falsifiability that was most strongly propounded by Popper has two
foundations: That there must be given some clear criterion to
statements from non-scientific
statements, such as metaphysical or
theological statements, and that the
criterion of verifiability, that was proposed by the neo-positivists,
was mistaken as a criterion.
One may well be somewhat skeptical about the first claim, for even if
there is a fundamental distinction between science and non-science it is
not necessary that this corresponds to some clear and simple criterion that is
applicable to all statements and that then unmistakenly selects just those
statements that are properly scientific.
And one may also hold that there is no simple criterion that makes
such a distiinction for all the sciences, and that this is not necessary
either, for what characterizes a science is usually clear enough, even
if it does not reduce to one single characteristic criterion that
distinguishes all statements of any science from any statements that are
not scientific: Empirical investigation of aspects of the real world, by
methods that are objective and capable of being employed by anybody
qualified, directed by empirical findings and logical argumentations,
and done in an objective, honest and controllable way.
It seemed to the neo-positivists that it is quite important to
distinguish science from non-science, and especially from metaphysics
and theology, and it seemed to them that they had found a simple
criterion to make the distinction: A statement is scientific, the
neo-positivists claimed, if and only if the statement is verifiable, and
then by an appropriate scientific method, included observation and
There are quite a few possible rational objections to this, and one
important one was strongly argued by Popper: The problem for a
scientific theory that gets verified by some of its logical
consequences, is that it does not get proved true by such confirmations,
and to believe that it does is to assume the fallacy of affirming the
This involves that if A implies B and B is found to be true, it is
not a logically valid conclusion that then A is true, and indeed to
argue this way ("A implies B. B is true. Therefore A must be true.")
that is a fallacy in deductive logic: If all cats are mammals, and this
is a mammal, it doesn't deductively follow that this is a cat.
Popper argued that in contrast to verifiability, the criterion that a
theory must be falsifiable is a good way to distinguish science from
non-science. His main logical reason was that if A implies B and B is
false, then it follows deductively that A is false.