expressed by co-ordinating with them in the schema the mark "T" (true).
Absence of this mark means disagreement.
4.431 The expression of the agreement and disagreement with the truth-possibilities of the elementary-propositions expresses the truth-conditions of the proposition. The proposition is the expression of its truth- conditions.
(Frege has therefore quite rightly put them at the beginning, as explaining the signs of his logical symbolism. Only Frege's explanation of the truth-concept is false: if "the true" and "the false" were real objects and the arguments in ~p etc., then the sense of ~p would by no means be determined by Frege's determination.)
4.44 The sign which arises from the co-ordination of that mark "T" with the truth-possibilities is a propositional sign.
4.441 It is clear that to the complex of the signs "F" and "T" no object (or complex of objects) corresponds; any more than to horizontal and vertical lines or to brackets. There are no "logical objects".
Something analogous holds of course for all signs, which express the same as the schemata of "T"and "F".
4.442 Thus e.g.
| " |
|
" |
is a propositional sign.
(Frege's assertion sign " |- " is logically altogether