An analogy for the theory of truth: Consider a black patch
on white paper; then we can describe the form of the patch by mentioning,
for each point of the surface, whether it is white or black.
To the fact that a point is black corresponds a positive fact, to the
fact that a point is white (not black) corresponds a negative
fact.
If I designate a point of the surface (one of
Frege's
“truth-values”), this is as if I set up an
assumption to be decided upon.
But in order to be able to say of a point that it is black or that it
is white, I must first know when a point is to be called black and when
it is to be called white.
In order to be able to say that “p” is true (or false), I
must first have determined under what circumstances I call a proposition
true, and thereby I determine the
sense of a
proposition.
The point in which the analogy fails is this: I can indicate a
point of the paper what is white
and black, but to a proposition without sense nothing corresponds, for
it does not designate a thing (truth-value), whose properties
might be called “false” or “true”; the
verb of a proposition is not “is true” or “is
false”, as Frege
believes, but what is true must already contain the verb.
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