The verification principle
A sentence has cognitive meaning if and only if it is analytic or in principle empirically verifiable. Metaphysical sentences are neither.
The Twentieth Century to Today · 1891 – 1970
Rudolf Carnap
卡尔纳普
Leading figure of the Vienna Circle: meaningful propositions must be verifiable, metaphysics consists of meaningless pseudo-propositions, and philosophy is the logical syntax of the language of science.
In logic there are no morals. Everyone is at liberty to build up his own logic, i.e. his own form of language, as he wishes.
Source: The Logical Syntax of Language, §17
Carnap was born in western Germany to a devout family of ribbon-weavers, studied physics, mathematics and philosophy at Jena and Freiburg, and was a student of Frege. He served three years at the front in the First World War, then studied physics in Berlin, and the war turned him toward pacifism and socialism. His doctorate of 1921 was on the concept of space. In 1926 Schlick invited him to Vienna as a lecturer, and he joined the discussion group around Schlick that became the Vienna Circle.
The Logical Structure of the World (1928) tried to define every scientific concept step by step in modern logic from 'elementary experiences' and a single relation of remembered similarity, so that physical objects, other minds and cultural objects could all be 'constructed'. In 1929 the Circle issued its manifesto, The Scientific Conception of the World, and in 1932 he published The Elimination of Metaphysics through Logical Analysis of Language, using Heidegger's 'the nothing itself nothings' to show that metaphysical sentences are grammatically well formed but logically meaningless; they express an attitude to life, like music, while mistaking themselves for theory.
In 1931 he moved to Prague, and The Logical Syntax of Language (1934) proposed the 'principle of tolerance': in logic there are no morals, and everyone may build a language as they wish provided the rules are stated. Most philosophical problems are practical questions about which linguistic framework to adopt, not questions about reality. Threatened by Nazism he emigrated to America in 1935, teaching first at Chicago and then at UCLA, with Quine, Hempel and Reichenbach as colleagues or sparring partners.
In America he turned to semantics and inductive logic: Meaning and Necessity built an intensional semantics that laid the groundwork for modal logic, and Logical Foundations of Probability sought an exact measure of degree of confirmation for inductive inference. Quine's 'Two Dogmas of Empiricism' (1951) attacked his analytic–synthetic distinction and his reductionism, and the debate marked the decline of logical positivism. He remained gentle to the end, answering every criticism seriously; students called him the most rational person they had ever met.
Key Ideas
The elimination of metaphysics
Metaphysics is not false theory but pseudo-proposition: like music it expresses a feeling for life, but in the disguise of theory.
The principle of tolerance
In logic there are no morals. Everyone may build their language as they wish; the only requirement is to state the syntactic rules.
Internal and external questions
'Are there numbers?' is trivially true inside the arithmetical framework; as a question outside any framework it has no cognitive content, only the practical decision whether to adopt the framework.
The unity of science
All the sciences can be expressed in one physicalist language. Psychological sentences can be translated into sentences about bodily behaviour.
Influenced by
- Gottlob Frege
He was one of Frege's very few students at Jena, attending three courses between 1910 and 1914, which he called the source of his whole logical training.
- Bertrand Russell
Having read Principia he wrote asking for a copy; Russell, unable to afford one, copied out the main definitions by hand and sent them. The Aufbau carried out Russell's programme of 'logical construction'.
- Ludwig Wittgenstein
The Vienna Circle read the Tractatus sentence by sentence; from it he took that logical truths are tautologies and metaphysics is meaningless, though the two men's meetings were strained.
- Immanuel Kant
- David Hume
Influenced
- Karl Popper
Often counted among the Vienna Circle, he was its 'official opposition': verifiability cannot demarcate science from non-science, only falsifiability can.
- W. V. O. Quine
He heard Carnap lecture in Prague in 1933 and called it his 'first intellectual engagement'; his life's work was a running argument with Carnap that ended by dismantling the analytic–synthetic distinction.
- Thomas Kuhn
- Hilary Putnam
In the 1950s he was Carnap's assistant and one of his earliest critics: the analytic–synthetic distinction is not simply wrong, but matters both much more and much less than Carnap thought.
- Saul Kripke