Full Idea
In a quantified language it is possible to build new sentences by combining two expressions neither of which is itself a sentence.
Gist of Idea
In quantified language the components of complex sentences may not be sentences
Source
Richard L. Kirkham (Theories of Truth: a Critical Introduction [1992], 5.4)
Book Reference
Kirkham,Richard L.: 'Theories of Truth: a Critical Introduction' [MIT 1995], p.150
A Reaction
In propositional logic the components are other sentences, so the truth value can be given by their separate truth-values, through truth tables. Kirkham is explaining the task which Tarski faced. Truth-values are not just compositional.
Related Idea
Idea 19316 Insight: don't use truth, use a property which can be compositional in complex quantified sentence [Tarski, by Kirkham]