Logical positivism

Logical positivism (later referred to as logical empiricism) holds that philosophy should aspire to the same sort of rigor as science. Philosophy should provide strict criteria for judging sentences true, false and meaningless.

Criticisms

Critics of Logical Positivism say that its fundamental tenets could not themselves be formulated in a way that was clearly consistent. The verifiability criterion of meaning did not seem verifiable; but neither was it simply a logical tautology, since it had implications for the practice of science and the empirical truth of other statements. This presented severe problems for the logical consistency of the theory. Another problem was that, while positive existential claims (There is at least one human being) and negative universals (Not all ravens are black) allow for clear methods of verification (find a human or a non-black raven), negative existential claims and positive universal claims do not.

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Universal claims could apparently never be verified: How can you tell that all ravens are black, unless you've hunted down every raven ever, including those in the past and future? This led to a great deal of work on induction, probability, and "confirmation," (which combined verification and falsification; see below).

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Karl Popper, a well known critic of Logical Positivism, published the book Logik der Forschung (Eng.:The Logic of Scientific Discovery) in 1934. In it he presented an influential alternative to the verifiability criterion of meaning, defining scientific statements in terms of falsifiability. First, though, Popper's concern was not with distinguishing meaningful from meaningless statements, but distinguishing scientific from metaphysical statements. He did not hold that metaphysical statements must be meaningless; neither did he hold that a statement that in one century was metaphysical, while unfalsifiable (like the ancient Greek philosophy about atoms), could not in another century become falsifiable, and thus scientific (by the 20th century atoms would become part of science). About psychoanalysis he thought something similar: in his day it offered no method for falsification, and thus was not falsifiable and not scientific, but he didn't exclude it being meaningful, nor did he say psychoanalists were necessarily wrong (it only couldn't be proven either way: that would have meant it was falsifiable), nor did he exclude that one day psychoanalysis could evolve into something falsifiable, and thus scientific. He was, in general, more concerned with scientific practice than with the logical issues that troubled the positivists. Second, although Popper's philosophy of science enjoyed great popularity for some years, if his criterion is construed as an answer to the question the positivists were asking it turns out to fail in exactly parallel ways. Negative existential claims (There are no unicorns) and positive universals (All ravens are black) can be falsified, but positive existential and negative universal claims cannot.

Related Topics:
Karl Popper - Logik der Forschung - Falsifiability - Atom

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Logical positivists' response to the first criticism is that Logical Positivism, like all other philosophies of science, is a philosophy of science, not an axiomatic system that can prove its own consistency. (see Gödel's incompleteness theorem) Secondly, a theory of language and mathematical logic were created to answer what it really means to say things like "all ravens are black".

Related Topics:
Axiomatic system - Gödel's incompleteness theorem - Theory of language - Mathematical logic

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A response to the second criticism was provided by A. J. Ayer in Language, Truth and Logic, in which he sets out the distinction between 'strong' and 'weak' verification. "A proposition is said to be verifiable, in the strong sense of the term, if, and only if, its truth could be conclusively established by experience." (Ayer 1946:50) It is this sense of verifiable that causes the problem of verification with negative existential claims and positive universal claims. However, the weak sense of verification states that a proposition is "verifiable... if it is possible for experience to render it probable." (ibid) After establishing this distinction, Ayer goes on to claim that "no proposition, other than a tautology, can possibly be anything more than a probable hypothesis" (Ayer 1946:51) and therefore can only be subject to weak verification. This defence was controversial among Logical Positivists, some of whom stuck to strong verification, and claimed that general propositions were indeed nonsense.

Related Topics:
A. J. Ayer - Tautology - Hypothesis

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Subsequent philosophy of science tends to make use of the better aspects of both of these approaches. Work by W. V. Quine and Thomas Kuhn has convinced many that it is not possible to provide a strict criterion for good or bad scientific method outside of the science we already have. But even this sentiment was not unknown to the logical positivists: Otto Neurath famously compared science to a boat which we must rebuild on the open sea.

Related Topics:
W. V. Quine - Thomas Kuhn - Otto Neurath

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