Inspired by Wittgenstein's Tractatus Logico-Philosophicus, the philosophers of the Vienna Circle devised a new system of philosophy that would eliminate confusions that originate from the misuse of language. Thus was born Logical Positivism.
The founding principle of the logical positivists was the Principle of Verifiability. The Principle held that the semantic meaning of your proposition is found in the way that you would verify its truth. If you don't know how to verify (or disprove) your proposition, then your proposition lacks semantic meaning, and your proposition is nonsensical to you.
Initially, the standard of verifiability required the possibility of positive scientific proof. Every meaningful proposition was either anayltic (true in light of definitions) or scientifically provable through empirical means. This elegant philosophical system grew to dominate philosophy in the middle of the 20th century.
However, cracks in the system began to appear almost immediately. Positive scientific proof turned out to be too strong a requirement because scientific consensus is contingent on data collected so far. Karl Popper introduced the notion of falsifiability. Ultimately, the other principles of logical positivism were also challenged, and positivism was cast aside.
Nevertheless, isn't there something sensible and salvageable in the Principle of Verifiability? If you can't say what experiences count as evidence for your proposition versus against it, do you really know what your proposition means?