the meaning of a proposition is its method of verification or falsification.A common criticism of logical positivism is that the Principle of Verifiability is not itself verifiable or falsifiable. As I shall show, the Principle meets its own criteria.
The Principle is not an empirical observation. The Principle defines meaning as being equivalent to "having logical consequences". Being a definition for a property, the Principle's own meaning merely requires that there be a recipe for determining the value of that property. Given a proposition, the recipe is straightforward: identify other propositions (physical or analytical) that are implied by or that refute the proposition under scrutiny.
The reader may object to the use of an arbitrary definition as the founding principle of a philosophy. Who is to say what the definition of meaning really is?
Well, the logical positivist definition of meaning sets the bar very low. It would be unreasonable to say that we would know the meaning of a proposition if we could not say what the implications of that proposition were. In other words, if you want to dispute the Principle of Verifiability, you would have to claim that a proposition has meaning or sense even when one cannot state what other propositions (again, empirical or analytic) would be implied or negated by its truth.
Thus, the Principle of Verifiability is a definition, much like the definition of any other mathematical concept like "prime number". It meets its own criteria of verifiability because it lays out a procedure for determining whether a proposition has meaning, just as the Sieve of Eratosthenes lays out a procedure for finding prime numbers.
To abandon the Principle of Verifiability is to admit that a proposition can have meaning even when it has no implications.