Full Idea
By a 'propositional function' I mean something which contains a variable x, and expresses a proposition as soon as a value is assigned to x. That is to say, it differs from a proposition solely by the fact that it is ambiguous.
Gist of Idea
'Propositional functions' are ambiguous until the variable is given a value
Source
Bertrand Russell (The Theory of Logical Types [1910], p.216)
Book Reference
Russell,Bertrand: 'Essays in Analysis', ed/tr. Lackey,Douglas [George Braziller 1973], p.216
A Reaction
This is Frege's notion of a 'concept', as an assertion of a predicate which still lacks a subject.
Related Idea
Idea 8488 A concept is a function whose value is always a truth-value [Frege]