Which of the following is an incorrect application of Leibniz's law?
A) inferring Fa ⋁ Fb from Fa ⋁ Fa and a = b
B) inferring (x)(Fx → Fb) from (x)(Fx → Fc) and b = c
C) inferring ($x)(Fx → Fx) from ($x)(Fx → Fy) and x = y
D) inferring (x)Fx → Gb from (x)Fx → Gz and z = b

Question

Quizplus · Accepted Answer

Leibniz's law allows substitution of identicals, but in option C, the substitution is incorrectly applied to a quantified statement, which does not preserve the logical structure.

Which of the Following Is an Incorrect Application of Leibniz's