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“”I suppose the most important [defect]…was that nearly all of it was false.
Logical positivism is a school of philosophy that emerged out of the Vienna Circle in the early 20th century. Its proponents emphasize materialism, empiricism, philosophical naturalism and the scientific method as the highest pursuits of rational thought. The most famous principle of logical positivism is that any statement that is not inherently verifiable is meaningless and can be safely ignored. Since this statement is itself inherently unverifiable, logical positivism tells us that logical positivism can be safely ignored. An alternative would be to take logical positivism as a foundational philosophy, like an axiom which needs no justification except that it works.
The philosophy was mostly reverse-engineered to explain the success of the scientific method. The claim that the positivists thought that much of ethics, theology and the supernatural would be reduced to nonsense is false. As Carnap stated, these things are framework dependent (just like gauge theories depend on a gauge that you can freely choose) and belong to the arts and not to science, philosophy would under this view also not be useless because it is useful as a tool to analyse scientific theories. It stresses skepticism, science, and reasoning grounded in an empirical reality that can be objectively perceived by all parties.
While there are some fundamental issues with logical positivism that have led to it being abandoned as a universal epistemological system, the thrust of its main argument has not been similarly dismissed. Many scientists like to talk about methodological naturalism or concepts such as NOMA as a way of allowing theological considerations to still hold some level of sway in a reality that is being increasingly defined and understood by a process that assumes the question if there is a God is meaningless. At some point it becomes reasonable to ask: if all of our best knowledge comes from a system that assumes that questions about the supernatural are meaningless, why do we need such a cause to begin with? Positivists would hold such claims are inherently lacking in meaning and substance, and that we are better off tossing them out.
Given its pedigree, it is unsurprising that positivism has a very narrow applicability and labels many traditional fields of philosophy that do not meet the verifiability criterion as meaningless. Disciplines like metaphysics and ethics that are unable to produce non-tautological, testable statements are rejected as mere speculation. While this principle may seem appealing for philosophers trying to establish the boundaries of science, it is a very restrictive view. If positivism is interpreted as a general epistemological position instead of a contribution to the narrower philosophy of science, it would necessitate abandoning all knowledge that is not either empirically derived or true by definition (like mathematics or the rules of logic itself). This does breed the danger of throwing the baby out with the bathwater - the criterion that is used to discriminate between sophistry and meaningful statements is very broad. Additionally, many valid scientific hypotheses concern themselves with processes and entities that are not, or at least not yet, immediately observable (for example, some postulated subatomic particles in the field of quantum mechanics). But anyway, in physics, there are several applications of the principle that lead to paradigm shifts, a few are listed here.
- Fields: the notion of fields, which is so abstract, acquires meaning through positivism. How can you tell if a field is there? Put a charge there and see it move! This positivist formulation was important in making clear that a concept that seems so immaterial to many people at first glance is in fact real.
- Luminiferous ether: the ether lost its material characteristics one by one, and it was an act of positivism by Einstein to reject the ether completely, because it had become unobservable.
- Equivalence principle: In order to get from the fact that you can't observe gravity in a free-falling frame to the principle that gravity is a geometric force, Einstein made an act of positivism. If the effects of acceleration are indistinguishable from gravity, then gravity and acceleration must be the same thing in essence. This is a very predictive statement.
- String theory: String theory emerged from a positivistic question--- how can you make a measurement in a space-time that is not well defined at short distances? The answer was to speak about s-matrix states, and their scattering. In physics, the resulting S-matrix theory led to string theory, which is the only candidate for a theory of everything.
- Black hole interiors/holography: Within string theory, the rejection of the simultaneous existence of the interior and exterior (since each are observed by different observers) led to the fruitful principles of black-hole complementarity and holography as developed by Susskind.
- Quantum Mechanics: The empirical results are independent of the interpretation.
Logical positivism is criticized for being self-refuting. Positivism asserts that any statement that cannot be empirically tested is meaningless. However, logical positivism is a philosophy, and cannot be empirically tested itself. By its own criterion, therefore, logical positivism is meaningless. This problem is by no means restricted to positivism, but more of an issue with sweeping, universal statements in general. No philosophy can explain "everything," or if it tries to, it will fail to be internally consistent. This is comparable to the mathematical concept of Gödel's incompleteness theorems.
Additionally, the criterion of verifiability was attacked as being overly restrictive, and posing a serious problem especially when applied to negative statements. Most notably, Karl Popper's proposition of falsifiability as a central characteristic of scientific statements was a direct reaction to ameliorate this issue.
 Role in modern philosophy
While logical positivism has been almost completely abandoned as a comprehensive epistemological position, it did make some positive contributions, particularly to the philosophy of science. The principle it uses for determining which statements are "meaningful" can be utilized as a solution of the demarcation problem when applied in a narrower sense of obtaining scientific knowledge. Its importance as a major step in the development of the philosophy of science is signified by the label "post-positivist" as a description for a range of modern formulations that typically take a more pragmatic and less universalist approach.
Despite its deficiencies, logical positivism has been highly influential in the development of philosophy of language and analytic philosophy in general. David Chalmers, for instance, sees some of his recent work as an attempt to rehabilitate Rudolf Carnap's Der logische Aufbau der Welt.
 See also
- Wikipedia has a pretty good article on logical positivism — the "basic tenets" and "criticism and influences" sections are very good.
- The Stanford Encyclopedia of Philosophy has an article on the Vienna Circle that covers the tenets of logical positivism in detail.
- A.J. Ayer on Logical Positivism: Section 1, Section 2, Section 3, Section 4
- ↑ Ayer interview with Bryan Magee
- ↑ Massimo Pigliucci: Nonsense on Stilts. Chicago: University of Chicago Press, 2010.
- ↑ Duke University:A Philosophical Discourse on Language