 This principle asserts: the course-of-values of the function \(f\) is identical to the course-of-values of the function \(g\) if and only if \(f\) and g map every object to the same value. [Actually, Frege uses an identity sign instead of the biconditional sign as the main connective of the principle. The reason he could do this is that, in his system, when two sentences are materially equivalent, they name the same truth value.] We shall soon see why this principle is inconsistent. 