Verificationism, also known as the verification principle or the verifiability criterion of meaning, is a doctrine in philosophy which asserts that a statement is meaningful only if it is either empirically verifiable (can be confirmed through the senses) or a tautology (true by virtue of its own meaning or its own logical form). Verificationism rejects statements of metaphysics, theology, ethics and aesthetics as meaningless in conveying truth value or factual content, though they may be meaningful in influencing emotions or behavior.

Verificationism was a central thesis of logical positivism, a movement in analytic philosophy that emerged in the 1920s by philosophers who sought to unify philosophy and science under a common naturalistic theory of knowledge. The verifiability criterion underwent various revisions throughout the 1920s to 1950s. However, by the 1960s, it was deemed to be irreparably untenable. Its abandonment would eventually precipitate the collapse of the broader logical positivist movement.

The roots of verificationism may be traced to at least the 19th century, in philosophical principles that aim to ground scientific theory in verifiable experience, such as C.S. Peirce's pragmatism and the work of conventionalist Pierre Duhem, who fostered instrumentalism. According to Gilbert Ryle, William James' pragmatism was "one minor source of the Principle of Verifiability". Verificationism, as principle, would be conceived in the 1920s by the logical positivists of the Vienna Circle, who sought an epistemology whereby philosophical discourse would be, in their perception, as authoritative and meaningful as empirical science. The movement established grounding in the empiricism of David Hume, Auguste Comte and Ernst Mach, and the positivism of the latter two, borrowing perspectives from Immanuel Kant and defining their exemplar of science in Einstein's general theory of relativity.

Ludwig Wittgenstein's Tractatus, published in 1921, established the theoretical foundations for the verifiability criterion of meaning. Building upon Gottlob Frege's work, the analytic–synthetic distinction was also reformulated, reducing logic and mathematics to semantical conventions. This would render logical truths (being unverifiable by the senses) tenable under verificationism, as tautologies.

Logical positivists within the Vienna Circle recognized quickly that the verifiability criterion was too stringent. Specifically, universal generalizations were noted to be empirically unverifiable, rendering vital domains of science and reason, including scientific hypothesis, meaningless under verificationism, absent revisions to its criterion of meaning.

Rudolf Carnap, Otto Neurath, Hans Hahn and Philipp Frank led a faction seeking to make the verifiability criterion more inclusive, beginning a movement they referred to as the "liberalization of empiricism". Moritz Schlick and Friedrich Waismann led a "conservative wing" that maintained a strict verificationism. Whereas Schlick sought to redefine universal generalizations as tautological rules, thereby to reconcile them with the existing criterion, Hahn argued that the criterion itself should be weakened to accommodate non-conclusive verification. Neurath, within the liberal wing, proposed the adoption of coherentism, though challenged by Schlick's foundationalism. However, his physicalism would eventually be adopted over Mach's phenomenalism by most members of the Vienna Circle.

With the publication of the Logical Syntax of Language in 1934, Carnap defined ‘analytic’ in a new way to account for Gödel's incompleteness theorem, who ultimately "thought that Carnap’s approach to mathematics could be refuted." This method allowed Carnap to distinguish between a derivative relation between premises that can be obtained in a finite number of steps and a semantic consequence relation that has on all valuations the same truth value for the premise as the consequent. It follows that all sentences of pure mathematics individually, or their negation, are "a consequence of the null set of premises. This leaves Gödel’s results completely intact as they concerned what is provable, that is, derivable from the null set of premises or from any one consistent axiomatization of mathematical truths."

In 1936, Carnap sought a switch from verification to confirmation. Carnap's confirmability criterion (confirmationism) would not require conclusive verification (thus accommodating for universal generalizations) but allow for partial testability to establish degrees of confirmation on a probabilistic basis. Carnap never succeeded in finalising his thesis despite employing abundant logical and mathematical tools for this purpose. In all of Carnap's formulations, a universal law's degree of confirmation was zero.