 Leibniz’s rejection of materialist conceptions of the mind was coupled with a strong opposition to dualistic views concerning the relationship between mind and body, particularly the substance dualism that figured in the philosophy of Descartes and his followers. According to this dualism, the world fundamentally consists of two disparate substances: extended material substance (body) and unextended thinking substance (mind). This bifurcation, of course, carries no burden of holding that the operations of the mental are realized by the operations of the physical. But despite his claim that consciousness and perception cannot be realized by, nor reduced to, the mechanical operations of matter, Leibniz found the alternative of postulating two distinct kinds of substance equally implausible.