Editing Rudolf Carnap (section)

=== ''Der Logische Aufbau der Welt''<!--'Constitution theory' redirects here--> ===
From 1922 to 1925, Carnap worked on a book which became one of his major works, namely ''Der logische Aufbau der Welt'' (translated as ''The Logical Structure of the World'', 1967), which was accepted in 1926 as his [[habilitation]] thesis at the [[University of Vienna]] and published as a book in 1928.<ref>Christian Damböck (ed.), ''Influences on the Aufbau'', Springer, p. 55.</ref> That achievement has become a landmark in modern epistemology and can be read as a forceful statement of the philosophical thesis of logical positivism. Indeed, the ''Aufbau'' suggests that epistemology, based on modern [[symbolic logic]], is concerned with the logical analysis of scientific propositions, while science itself, based on experience, is the only source of knowledge of the external world, i.e. the world outside the realm of human perception. According to Carnap, philosophical propositions are statements about the language of science; they aren't true or false, but merely consist of definitions and conventions about the use of certain concepts. In contrast, scientific propositions are factual statements about the external reality. They are meaningful because they are based on the perceptions of the senses. In other words, the truth or falsity of those propositions can be verified by testing their content with further observations.

In the ''Aufbau'', Carnap wants to display the logical and conceptual structure with which all scientific (factual) statements can be organized. Carnap gives the label "'''constitution theory'''<!--boldface per WP:R#PLA-->" to this epistemic-logical project. It is a constructive undertaking that systematizes scientific knowledge according to the notions of symbolic logic. Accordingly, the purpose of this constitutional system is to identify and discern different classes of scientific concepts and to specify the logical relations that link them. In the Aufbau, concepts are taken to denote objects, relations, properties, classes and states. Carnap argues that all concepts must be ranked over a hierarchy. In that hierarchy, all concepts are organized according to a fundamental arrangement where concepts can be reduced and converted to other basic ones. Carnap explains that a concept can be reduced to another when all sentences containing the first concept can be transformed into sentences containing the other. In other words, every scientific sentence should be translatable into another sentence such that the original terms have the same reference as the translated terms. Most significantly, Carnap argues that the basis of this system is psychological. Its content is the "immediately given", which is made of basic elements, namely perceptual experiences. These basic elements consist of conscious psychological states of a single human subject. In the end, Carnap argues that his constitutional project demonstrates the possibility of defining and uniting all scientific concepts in a single conceptual system on the basis of a few fundamental concepts.