Incomplete symbol
Incomplete symbol
A symbol (or expression) which has no meaning in isolation but which may occur as a constituent part in, and contribute to the meaning of, an expression which does have a meaning. Thus — as ordinarily employed — a terminal parenthesis ) is an incomplete symbol, likewise the letter ? which appears in the notation for functional abstraction (q. v.), etc.
An expression A introduced by contextual definition — i.e., by a definition which construes particular kinds of expressions containing A, as abbreviations or substitutes for certain expressions not containing A, but provides no such construction for A itself — is an incomplete symbol in this sense. In Principia Mathematica, notations for classes, and descriptions (more correctly, notations which serve some of the purposes that would be served by notations for classes and by descriptions) are introduced in this way by contextual definition. — A. C.
Whitehead and Russell, Principia Mathematica, vol. 1.