propositions, and is to be found in the realm of logic and mathematics, must be explained on coherence, but the truth of all propositions expressing real knowledge (which, in a sense is the only important kind) must be regarded as a correspondence between a fact and the sentence which expresses it.
The chief argument against the correspondence view asserts that it is impossible to compare our propositions with reality, because reality is not known to us except through our propositions, so that in the end the mutual coherence of the latter remains the only criterion. But this argument rests on the strange assumption of a metaphysical dualism, as if there were a realm of propositions apart and mysteriously separated from the realm of reality.
As a matter of fact there is no difficulty in carrying out the required comparison. Every proposition is given empirically as a spoken or written sentence, a complex of physical signs, which is itself a fact in the real world: comparing a proposition with the state of affairs it expresses is, therefore, nothing but a comparison of two facts. It is something we do a hundred times every day of our lives, and nobody can very well deny the possibility of it.
A proposition will be verified, the truth will be established if the structure is the same as the structure of the fact it tries to express. Certainly the two facts (the sentence and the state of affairs it communicates) are always very different from each other — how can they have the same logical structure? We must remember that the sentence has been given a logical structure and a meaning only by assigning definite significations to its parts; it is only through this interpretation that it has become a proposition at all (instead of remaining a simple ordinary dead fact) and has become coordinated to the expressed fact. The logical structure of the proposition has of course, very little to do with the linguistic grammatical structure of the sentence and is ever so much more complicated. In order to get at it we must imagine all the words of the sentence to be replaced by their definitions, the terms occurring in the definitions must be replaced by sub-definitions, and so on until we reach the boundary of ordinary verbal language where it ends in gestures or prescriptions to perform certain acts. In some cases where no explicit definition of a term is possible, the whole sentence will have to be transformed into a new shape, and the actual procedure of finding its meaning
