Positivism

What follows is a list of several interlocking theses and projects and their outcomes, several of which were controversial among the LEs themselves.

1. The verifiability theory of meaning.

A sentence is empirically meaningful if and only if it is verifiable in principle and (roughly) its meaning is given by the method of its verification. The LEs quickly rejected full verifiability in favor of weaker forms of testability. However, they were never able to formulate an adequate formal criterion of meaning or justify the equation of meaning with empirical evidence. It was this "verificationism" that backed the LEs' anthropomorphic claim that all genuine problems are empirical and therefore humanly solvable and their dismissal of all metaphysical problems as pseudoproblems. Since competing metaphysical positions, by definition, have no empirical consequences, they cannot differ in meaning; so there can be no meaningful problem of choosing between them.

2. The attack on metaphysics as meaningless.

The LEs agreed that an enlightened society has no room for metaphysics; however, they sometimes disagreed over what counts as metaphysics.

3. A sharp fact-value distinction and emotive ethics.

Ethical and aesthetic utterances are emotional reactions. Since they are not empirically testable, they have no cognitive meaning and cannot be true or false. Nonetheless, the early LEs took a strong normative stance on social and political issues.

4. The observational-theoretical distinction.

The project to distinguish epistemically unproblematic observational terms and sentences from the theoretical ones and legitimize the latter in terms of their logical relations to the former ran into similar difficulties despite important progress such as Carnap's treatment of dispositional terms. N. R. Hanson, Popper, Kuhn, Paul Feyerabend, and Putnam noted that scientific observational language is "theory laden" and that there is no context-free, linear gradation of theoreticity.

5. The analytic-synthetic distinction.

Quine's influential critique of this pillar of LE (and of much else), in "Two Dogmas of Empiricism" and other writings, and his return to a pragmatic naturalism were heavy blows. The second dogma was "radical reductionism," the idea that each sentence in isolation can be correlated with a range of experience.

6. Application of the resources of the new symbolic logic and the third dogma.

The LEs (especially Carnap) developed and applied the new symbolic logic in ingenious ways, mainly in terms of purely syntactic rules; but later critiques by Quine, Hempel, Nelson Goodman, and others showed that semantic and pragmatic considerations are unavoidable, effectively dooming Carnap's project to produce objective, ahistorical, context-free languages of science. By the 1950s and 1960s, philosophers increasingly felt that the LEs had exhausted the resources of deductive logic without adequately capturing the richness of scientific reasoning. Static logical relations seemed especially incapable of modeling scientific theories and deep conceptual change, for example, scientific revolutions. Commitment to deductive logic by the LEs and Popper has been called the third dogma of empiricism. (Others, following Donald Davidson, give this label to the so-called scheme-content distinction.) Reichenbach all along had urged a probabilistic approach (a theme continued by his student, Salmon), although he and Carnap had developed probability theory in roughly opposite ways.

7. Logical analysis of scientific confirmation, explanation, and theory structure.

The LEs admirably articulated old and new ideas here in terms of detailed models. Their work set the standard for ongoing research in these areas. Hempel's extension of "covering law" explanation to history, psychology, and the social sciences was especially controversial since it challenged old ideas about human freedom and spontaneity and the need for sympathetic understanding. Yet it also failed to capture the force of causal explanation.

8. The unity of science.

Pitting the sciences against the rest of culture, some LEs defended the unity of science on three fronts: conceptual, doctrinal, and methodological. Conceptual unity means that there is one universal language of science; doctrinal unity, that more complex disciplines such as biology are ultimately reducible to more basic disciplines such as chemistry and physics; methodological unity states that there is one general method of science, that all legitimate theories, all explanations, and so on possess the same logical structure. All of these projects produced interesting results, but have since been abandoned. In the antireductionist, more pragmatic atmosphere of the early twenty-first century, the emphasis is on diversity, on teasing out the differences among the various sciences rather than on trying to model all of them on physics; and physics itself turns out to be internally diverse. Most experts reject the existence of a unique scientific method as a fiction of textbooks and school administrators.

9. The fall and rise of naturalistic epistemology.

Prominent LEs followed Gottlob Frege in sharply distinguishing logic and epistemology from psychology; "psychologism" was the fallacy of confusing them. It was on this point that the positivists differed most obviously from the American pragmatists. (As usual, the most important exception was Neurath, who promoted a naturalistic epistemology.) But the LEs' own critique of Kant's transcendental epistemology could be viewed as a step toward a naturalistic epistemology. Quine took the next step and urged a return to a naturalistic pragmatism, contending that epistemology should become a branch of behavioral psychology. Historical case studies by Kuhn, Feyerabend, and their followers showed that the failure of LE and Popperian methodologies to fit actual history was so great as to raise the question whether anything recognizable as science could fit the old rules of method. Since (as Kant said) "ought" implies "can," the critics thereby showed that empirical information is relevant to and can in a sense "refute" a methodology despite its normative character.

This surprising turn does fit Quine's pronouncement that "no statement is immune to revision," come what may—not a conventional or "analytic" statement or even a normative one. The critics increasingly perceived some problems in the philosophy of science as artifacts of the LE approach and hence as pseudoproblems with respect to real science. Kuhn famously distinguished normal science under a paradigm (a quasi-Kantian categorical scheme that made normal science possible and intelligible) from revolutionary science, neither of which fit the tenets of either LE or Popperianism. In "the battle of the big systems" (initially among the LEs, Popper, Kuhn, Feyerabend, Imre Lakatos, and Stephen Toulmin), many considered Kuhn the winner, although many philosophers severely criticized his work. And yet Carnap, who increasingly thought in terms of free, pragmatic choices among available linguistic frameworks, welcomed Kuhn's contribution as making a similar point. The work of Kuhn and Feyerabend brought all the above-mentioned difficulties of LE to a focus, which hastened its demise as the generally accepted account of science. No similarly grand consensus has replaced it.

10. The discovery-justification distinction.

This distinction was an LE bulwark against psychologism. The basic idea is that it does not matter how or why a theory or problem solution pops into someone's head; what matters is how the claim is tested. There is a psychology of discovery but no logic of discovery, only a logic of justification. Philosophy is concerned only with the logically reconstructed products and not the processes of science. The LEs' applications of the discovery-justification distinction drew philosophy of science closer to philosophical problems of logic and epistemology and away from the study of science as practiced by communities of scientists. Since the new historical case studies were precisely the study of the process of investigation, they challenged these applications.

11. The emergence of science studies.

As scientific insiders, the original LEs relied on their own knowledge and intuitions about how science works (or should work) and, qua analytic philosophers, saw no need for careful empirical studies of the sciences themselves. The Kuhnian revolution changed that. Their sharpest critics noted the irony that the logical empiricists urged everyone else to be empiricists but themselves! But while post-Kuhnian philosophers began to take the history of science seriously, they did not study in detail the scientific practices of contemporary science. They thereby left an opening for the new empirical sociology of scientific knowledge that has since grown into a multidisciplinary "science studies," often defined to exclude philosophy.

12. Realism versus social constructionism and "the science wars."

As strong empiricists, early LEs tended to advocate a minimalist stance toward theories and the entities that they appeared to postulate. Some regarded theories as instruments for calculation rather than as attempts truly to describe underlying reality. Carnap himself used Russell's maxim as a motto: "Wherever possible logical constructions are to be substituted for inferred entities." This is a logical constructionist position. Most science studies practitioners are also constructionists, but social constructionists. They deny that science is a special, epistemically privileged institution and regard its results as negotiated social constructions. In reaction, many philosophers now take a "realist" position that affirms objective, scientific progress toward truth and vigorously denies the cultural relativity of scientific results. As heirs of the Enlightenment, they reject the centrifugal tendencies of postmodernism and defend the special place of the sciences in human culture. This heated debate among philosophers, science studies practitioners, culture theorists, and scientists themselves is commonly known as "the science wars." If the postmodernist critics are right, Comte's law of three stages stopped at least one stage too soon!

13. The linguistic turn and the rise and fall of narrowly analytic philosophy.

With G. E. Moore, Russell, and the early Wittgenstein as precursors, the LEs, and especially Carnap, were the primary developers of analytic philosophy. After World War II, a wider sort of linguistic philosophy, "ordinary language philosophy," flourished at Oxford. Both movements construed philosophy itself as a metadiscipline concerned to analyze language rather than to address substantive questions about the world and human activity. But since the 1960s, Anglo-American philosophy has become more liberal in its interests and methods. Philosophers once again vigorously discuss the metaphysical issues rejected by the LEs as pseudoproblems, and there is even something of a rapprochement with the so-called Continental philosophy of Heidegger and his successors. Carnap dominated the American phase and the received view of LE; but at the turn of the twenty-first century, many experts were examining Neurath's position in greater detail and finding it more defensible.