What remains unchanged with a sentence when we replace a designator with a
Hence, the truth value is the reference of a sentence.
Frege holds that truth-values are actually objects, just like any other abstract
This means that a (declarative) sentence are in fact modes of presentation of one
of two truth-values: True or False.
The Thought is not the reference, but it is important, so what is its role?
Frege: the Thought (or a proposition) is the sense of a declarative sentence.
Empty reference principle: “the number given by adding 2 to the natural number
directly before 0” denotes nothing.