Logical Positivism

Logical Positivism (later also known as Logical Empiricism) is a theory in Epistemology and Logic that developed out of Positivism and the early Analytic Philosophy movement, and which campaigned for a systematic reduction of all human knowledge to logical and scientific foundations. Thus, a statement is meaningful only if it is either purely formal (essentially, mathematics and logic) or capable of empirical verification.

This effectively resulted in an almost complete rejection by Logical Positivists of Metaphysics (and to a large extent Ethics) on the grounds that it is unverifiable. Its influence in 20th Century Epistemology and Philosophy of Science, however, has been profound.

Most early Logical Positivists asserted that all knowledge is based on logical inference from simple "protocol sentences" grounded in observable facts. They supported forms of Materialism, Naturalism and Empiricism, and, in particular, they strongly supported the verifiability criterion of meaning (Verificationism), the doctrine that a proposition is only cognitively meaningful if it can be definitively and conclusively determined to be either true or false.

Logical Positivism was also committed to the idea of "Unified Science", or the development of a common language in which all scientific propositions can be expressed, usually by means of various "reductions" or "explications" of the terms of one science to the terms of another (putatively more fundamental) one.

The main tenets of the doctrine include:

• The opposition to all Metaphysics, especially ontology (the study of reality and the nature of being), not as necessarily wrong but as having no meaning.
• The rejection of synthetic a priori propositions (e.g. "All bachelors are happy"), which are, by their nature, unverifiable (as opposed to analytic statements, which are true simply by virtue of their meanings e.g. "All bachelors are unmarried").
• A criterion of meaning based on Ludwig Wittgenstein's early work, (essentially, that the meaning of a word is its use in the language, and that thoughts, and the language used to express those thoughts, are pictures or representations of how things are in the world).
• The idea that all knowledge should be codifiable in a single standard language of science, and the associated ongoing project of "rational reconstruction", in which ordinary-language concepts were gradually to be replaced by more precise equivalents in that standard language.

The most important early figures in Logical Positivism were the Bohemian-Austrian Positivist philosopher Ernst Mach (1838 - 1916) and the Austrian Ludwig Wittgenstein (especially his "Tractatus" of 1921, a text of great importance for Logical Positivists).

Logical Positivism in Germany rose in response to the Metaphysics of Georg Hegel, which was the dominant philosophical view in Germany at the time, particularly the rejection of his concept of metaphysical entities that did not have any empirical basis.

It grew from the discussions of the so-called "Vienna Circle" of Moritz Schlick (1882 - 1936) in the early 20th Century. A 1929 pamphlet jointly written by Otto Neurath (1882 - 1945), Hans Hahn (1979 - 1934) and Rudolf Carnap (1891 - 1970) brought together some of the major proponents of the movement and summarized the doctrines of the Vienna Circle at that time. The contemporaneous Berlin Circle of Hans Reichenbach (1891 - 1953) also propagated the new doctrines more widely in the 1920s and early 1930s.

A. J. Ayer is considered responsible for the spread of Logical Positivism to Britain, and his 1936 book "Language, Truth and Logic" was very influential. Developments in logic and the foundations of mathematics, especially in the "Principia Mathematica" by the British philosophers Bertrand Russell and Alfred North Whitehead, particularly impressed the more mathematically-minded Logical Positivists.

The movement dispersed in the late 1930's, mainly because of political upheaval and the untimely deaths of Hahn and Schlick. Logical Positivism was essential to the development of early Analytic Philosophy, with which it effectively merged.

There were many internal arguments within the Logical Positivism movement, which in reality was only ever a loose collective of philosophers holding a wide range of beliefs on many matters, although with certain principles in common.

Critics have argued that Logical Positivism's insistence on the strict adoption of the verifiability criterion of meaning (the requirement for a non-analytic, meaningful sentence to be either verifiable or falsifiable) is problematic, as the criterion itself is unverifiable, especially for negative existential claims and positive universal claims.

Karl Popper (1902 - 1994) disagreed with the logical positivist position that metaphysical statements must be meaningless, and further argued that a metaphysical statement can change its unfalsifiable status over time - what may be "unfalsifiable" in one century may become "falsifiable" (and thus "scientific") in another.

A. J. Ayer responded to the charge of unverifiability by claiming that, although almost any statement (except a tautology or logical truth) is unverifiable in the strong sense, there is a weak sense of verifiability in which a proposition is verifiable if it is possible for experience to render it probable. This defense, however, was controversial among Logical Positivists, some of whom stuck to strong verification, and insisted that general propositions were indeed nonsense.

Hilary Putnam (1926 - ) has argued that making a distinction between "observational" and "theoretical" is meaningless. W. V. O. Quine has criticized the distinction between analytic and synthetic statements, and the reduction of meaningful statements to immediate experience. Thomas Kuhn (1922 - 1996) has argued that it is just not possible to provide truth conditions for science, independent of its historical paradigm.