In Plato's Republic one finds the proposition: God, being perfect, cannot change (not for the better, since "perfect" means that there can be no better; not for the worse, since ability to change for the worse, to decay, degenerate, or become corrupt, is a weakness, an imperfection). The argument may seem cogent, but it is so only if two assumptions are valid: that it is possible to conceive of a meaning for "perfect" that excludes change in any and every respect and that we must conceive God as perfect in just this sense.

Omnipotence and Other Theological Mistakes (1984)