The thought contains the possibility of the state of affairs which it thinks. What is thinkable is also possible.
We cannot think anything unlogical, for otherwise we should have to think unlogically.
It used to be said that God could create everything, except what was contrary to the laws of logic. The truth is, we could not say of an “unlogical” world how it would look.
To present in language anything which “contradicts logic” is as impossible as in geometry to present by its coordinates a figure which contradicts the laws of space; or to give the coordinates of a point which does not exist.
We could present spatially an atomic fact which contradicted the laws of physics, but not one which contradicted the laws of geometry.
An a priori true thought would be one whose possibility guaranteed its truth.
Only if we could know a priori that a thought is true if its truth was to be recognized from the thought itself (without an object of comparison).
In the proposition the thought is expressed perceptibly through the senses.
We use the sensibly perceptible sign (sound or written sign, etc. ) of the proposition as a projection of the possible state of affairs.
The method of projection is the thinking of the sense of the proposition.
The sign through which we express the thought I call the propositional sign. And the proposition is the propositional sign in its projective relation to the world.
To the proposition belongs everything which belongs to the projection; but not what is projected.
Therefore the possibility of what is projected but not this itself.
In the proposition, therefore, its sense is not yet contained, but the possibility of expressing it.
(“The content of the proposition” means the content of the significant proposition.)
In the proposition the form of its sense is contained, but not its content.
The propositional sign consists in the fact that its elements, the words, are combined in it in a definite way.
The propositional sign is a fact.
The proposition is not a mixture of words (just as the musical theme is not a mixture of tones).
The proposition is articulate.
Only facts can express a sense, a class of names cannot.
That the propositional sign is a fact is concealed by the ordinary form of expression, written or printed.
For in the printed proposition, for example, the sign of a proposition does not appear essentially different from a word.
The essential nature of the propositional sign becomes very clear when we imagine it made up of spatial objects (such as tables, chairs, books) instead of written signs.