 Causal Efficacy: In this argument, Malebranche begins by noting that ideas are causally efficacious ‘since they act upon the mind and enlighten it’ and ‘make it happy or unhappy through pleasant or unpleasant perceptions by which they affect it’ (3.2.6, OC 1:442; LO 232). To establish that these ideas are in God, he then invokes an Augustinian principle, namely that ‘nothing can act immediately upon the mind unless it is superior to it.’ To make sense of this principle, one must envisage, as Augustine did, a hierarchy of being in which minds are higher than bodies and God constitutes the upper limit of moral perfection. For Malebranche, these are the only substances there are. So it follows that only God can act on the soul and, insofar as they are efficacious, ideas must be the very substance of God.