Then the space in which apparent nature is set is the expression of certain relations between the apparent objects.

It is a set of apparent relations between apparent relata.

Apparent nature is the dream, and the apparent relations of space are dream relations, and the space is the dream space.

Similarly the space in which causal nature is set is the expression of certain relations between the causal objects.

It is the expression of certain facts about the causal activity which is going on behind the scenes.