Falsificationism was first introduced by Sir Karl Popper. It is a methodology of science. In particular, he introduced it as a criterion to demarcate science from non-science. It is also one response to “The
Problem of Induction”, where induction is another means of obtaining knowledge. Falsifiability states that the truths of science are arrived at through a series of conjectures and refutations. Because of the
problem of induction, we cannot consider truths that were arrived at inductively as “justified”. However, we can be “justified” in showing the falsity of a statement.
An example of a falsfiable conjecture: All orbits are circular. The way to falsify: find one that is not.
An example of an unfalsifiable conjecture: Scorpios are secretive. There is no clear test to disprove this.
Verificationism is the view that a statement only has meaning if there exists an empirical test to prove it (regardless of the practicability of such a test). “Meaning” is defined as having truth-value (that is, it can be true or false).
An example of a verifiable statement: Mercury’s orbit is circular. Why? Because we can observe that this is true or false.
An example of an unverifiable statement: Scorpios are secretive. Why? Because there is no empirical
test that would show this to be either true or false. Actually, I’d say that saying that it could be true or false is a false dichotomy.
Interestingly, NP-complete problems are technically verifiable, but not practically so.
Popper was a critic of verificationism. To Popper, scientific truth could not be arrived at by “verifying” a conjecture. Since induction was not "justified”, “truth” could only be arrived at through “conjectures and refutations”.
But Popper’s criterion of demarcation (i.e. his falsificationism) was a methodological norm, and not a theory of meaning, as verificationism is.