Theory, held briefly by Bertrand Russell (1872-1970) and Ludwig Wittgenstein (1889-1951) soon after World War I, that a proper description of reality would be in terms of atomic propositions, each containing a word standing for a quality or relation and one or more words standing for objects which had the quality or relation.
Atomic propositions are true or false according to whether they do or don't correspond to and picture atomic facts. Molecular propositions are formed from them by negation and connectives (primarily 'and', 'or', and 'if... then') which are truth-functional; that is, given the truth or falsity of its atomic propositions, the truth or falsity of a molecular proposition could be inferred.
The theory then claims that this apparatus is adequate for describing reality completely. However, problems arose in dealing with negation, general propositions, propositions about belief and other notions that appear to violate the extensionality thesis, and there was some vacillation on whether any non-atomic facts could be admitted.
D F Pears, Bertrand Russell and the British Tradition in Philosophy (1967)