Full Idea
When I judge 'Socrates is human', the meaning is completed by the act of judging, and we no longer have an incomplete symbol.
Gist of Idea
Only the act of judging completes the meaning of a statement
Source
B Russell/AN Whitehead (Principia Mathematica [1913], p.44), quoted by J. Alberto Coffa - The Semantic Tradition from Kant to Carnap
Book Reference
Coffa,J.Alberto: 'The Semantic Tradition from Kant to Carnap' [CUP 1993], p.145
A Reaction
Personally I would have thought that you needed to know the meaning properly before you could make the judgement, but then he is Bertrand Russell and I'm not.