---
title: "Logical positivism"
chunk: 4/5
source: "https://en.wikipedia.org/wiki/Logical_positivism"
category: "reference"
tags: "science, encyclopedia"
date_saved: "2026-05-05T03:39:44.646869+00:00"
instance: "kb-cron"
---

Carl Hempel was prominent in the development of the deductive-nomological (DN) model, then the foremost model of scientific explanation defended even among critics of neo-positivism such as Popper. According to the DN model, a scientific explanation is valid only if it takes the form of a deductive inference from a set of explanatory premises (explanans) to the observation or theory to be explained (explanandum). The model stipulates that the premises must refer to at least one law, which it defines as an unrestricted generalization of the conditional form: "If A, then B". Laws therefore differ from mere regularities ("George always carries only $1 bills in his wallet") which do not necessarily support counterfactual claims. Furthermore, laws must be empirically verifiable in compliance with the verification principle.
The DN model ignores causal mechanisms beyond the principle of constant conjunction ("first event A and then always event B") in accordance with the Humean empiricist postulate that, though sequences of events are observable, the underpinning causal principles are not. Hempel stated that well-formulated natural laws (empirically confirmed regularities) are satisfactory in approximating causal explanation.
Hempel later proposed a probabilistic model of scientific explanation: The inductive-statistical (IS) model. Derivation of statistical laws from other statistical laws would further be designated as the deductive-statistical (DS) model. The DN and IS models are collectively referred to as the "covering law model" or "subsumption theory", the latter referring to the movement's stated goals of "theory reduction".

=== Unity of science ===

Logical positivists were committed to the vision of a unified science encompassing all scientific fields (including the special sciences, such as biology, anthropology, sociology and economics, and the fundamental science, or fundamental physics) which would be synthesised into a singular epistemic entity. Key to this concept was the doctrine of theory reduction, according to which the covering law model would be used to interconnect the special sciences and, thereupon, to reduce all laws in the special sciences to fundamental physics.
The movement envisioned a universal scientific language that could express statements with common meaning intelligible to all scientific fields. Carnap sought to realise this goal through the systematic reduction of the linguistic terms of more specialised fields to those of more fundamental fields. Various methods of reduction were proposed, referring to the use of set theory to manipulate logically primitive concepts (as in Carnap's Logical Structure of the World, 1928) or via analytic and a priori deductive operations (as described in Testability and Meaning, 1936, 1937). A number of publications over a period of thirty years would attempt to elucidate this concept.

== Criticism ==
In the post-war period, key tenets of logical positivism, including the verifiability criterion, analytic-synthetic distinction and observation-theory distinction, drew escalated criticism. This would become sustained from various directions by the 1950s, so that, even among fractious philosophers who disagreed on the general objectives of epistemology, most would concur that the logical positivist program had become untenable. Notable critics included Karl Popper, W. V. O. Quine, Norwood Hanson, Thomas Kuhn, Hilary Putnam, as well as J. L. Austin, Peter Strawson, Nelson Goodman and Richard Rorty. Hempel himself became a major critic from within the movement, denouncing the positivist thesis that empirical knowledge is restricted to basic statements, observation statements or protocol statements.

=== Karl Popper ===
Karl Popper, a graduate of the University of Vienna, was an outspoken critic of the logical positivist movement from its inception. In Logik der Forschung (1934, published in English in 1959 as The Logic of Scientific Discovery) he attacked verificationism directly, contending that the problem of induction renders it impossible for scientific hypotheses and other universal statements to be verified conclusively. Any attempt to do so, he argued, would commit the fallacy of affirming the consequent, given that verification cannot—in itself—exclude alternative valid explanations for a specific phenomenon or instance of observation. He would later affirm that the content of the verifiability criterion cannot be empirically verified, thus is meaningless by its own proposition and ultimately self-defeating as a principle.
In the same book, Popper proposed falsifiability, which he presented, not as a criterion of cognitive meaning like verificationism (as commonly misunderstood), but as a criterion to distinguish scientific from non-scientific statements, thereby to demarcate the boundaries of science. Popper observed that, though universal statements cannot be verified, they can be falsified, and that the most productive scientific theories were apparently those that carried the greatest 'predictive risks' of being falsified by observation. He would conclude that the scientific method should be a hypothetico-deductive model, wherein scientific hypotheses must be falsifiable (per his criterion), held as provisionally true until proven false by observation, and are corroborated by supporting evidence rather than verified or confirmed.
In rejecting neo-positivist views of cognitive meaningfulness, Popper considered metaphysics to be rich in meaning and important in the origination of scientific theories and value systems to be integral to science's quest for truth. At the same time, he disparaged pseudoscience, referring to the confirmation biases that embolden support for unfalsifiable conjectures (notably those in psychology and psychoanalysis) and ad hoc arguments used to entrench predictive theories that have been proven conclusively false.

=== Willard V. O. Quine ===
In his influential 1951 paper Two Dogmas of Empiricism, American philosopher and logicist Willard Van Orman Quine challenged the analytic-synthetic distinction.  Specifically, Quine examined the concept of analyticity, determining that all attempts to explain the idea reduce ultimately to circular reasoning. He would conclude that, if analyticity is untenable, so too is the neo-positivist proposition to redefine its boundaries. Yet Carnap's reconstruction of analyticity was necessary for logic and mathematics to be deemed meaningful under verificationism. Quine's arguments encompassed numerous criticisms on this topic he had articulated to Carnap since 1933. His work effectively pronounced the verifiability criterion untenable, threatening to uproot the broader logical positivist project.