A = C;
and similarly from
(A) = (B) = (C),
meaning that the numbers of A’s and C’s are equal to the number of B’s, we can infer
(A) = (C).
But, curiously enough, this does not apply to negative propositions and inequalities. For if
A = B ~ D
means that A is identical with B, which differs from D, it does not follow that
(A) = (B) ~ (D).
Two classes of objects may differ in qualities, and yet they may agree in number. This point strongly confirms me in the opinion which I have already expressed, that all inference really depends upon equations, not differences.