If all causal production of mental and physical events originates solely in God, then God alone is the true cause.

Mental and physical substance are thus identical with God's causal production of the mental events constituting minds and the sensible ideas or “sensations” which constitute bodies “according to…methods and laws” which he has freely established (“The Mind,” no. 13; Edwards 1957–, vol. 6, 344). God is thus the only true substance as well as the only true cause.