Humans are pure mental substances, that is essentially souls, who have a rich mental life of sensations, thoughts, intentions, and other pure mental events, largely caused by and sometimes causing events in their brains and so in their bodies. God has reason to create humans because humans have a kind of goodness, the ability to choose between good and evil, which God himself does not have. The existence of these causal connections between mental events and brain events requires an enormous number of separate psychophysical laws. It is most improbable that there would be such laws if God had not made them. Each soul has a thisness; it is the particular soul it is quite independently of its mental properties and bodily connections. So no scientific law, concerned only with relations between substances in virtue of their universal properties, could explain why God created this soul rather than that possible soul, and connected it to this body. Yet a rational person often has to choose between equally good alternatives on non-rational grounds; and so there is nothing puzzling about God choosing to create this soul rather than that possible soul. Hence the existence of souls provides a good argument for the existence of God.