 It was also shaped by Leibniz's belief in the perfectibility of human nature (if humanity relied on correct philosophy and religion as a guide), and by his belief that metaphysical necessity must have a rational or logical foundation, even if this metaphysical causality seemed inexplicable in terms of physical necessity (the natural laws identified by science).Because reason and faith must be entirely reconciled, any tenet of faith which could not be defended by reason must be rejected.Leibniz then approached one of the central criticisms of Christian theism