this theory uses thinking to build a materialistic conception of the world, so uses thinking, that is an originary phenomenon, to say that the originary phenomenon is something material, that creates thinking.
It's like the "brain in a vat" theory: this theory exists thank to thinking as a spiritual activity, founded in itself: because even if we are not brains in a vat we can think that we are. It uses thinking to negate that thinking is a spiritual activity.
This is the power of thinking: it has also the power to negate itself!