You might want to read Schopenhauer who argues four points as well. You know I am dutch, so the words I use may not be the proper translation. Who knows my dabbling can get you anywhere.

The fourfold root of the law of sufficent cause.

Knowing causality is the only function of the intellect according to Schopenhauer. The first, always present aspect of the intellect is the observation of the phenomena. This is causal in all ways and thereby all perceptions are intellectual. Because of this the intellect is not seperate from percieving, nor of determining the relations. This is the basis for experiencing.

'The world is my imagination'

The four grounds:

1) Time and space are seperate grounds of being, a priori.
2) By the combination of time and space makes percieving possible for a subject.
3) It is possible for a knowing subject to know itself directly as "will".
4) These first three classes can only be deduced by placing something outside these mechanics. Judgements therefore are the abstract judgements grounded in intu?tions of time and space (external causality), ideas of perception or deads of free will (internal causality).

The first three rules are subsumed under the fourth. The thinprinciple itself and the thing in itself cannot be explained. Schopenhauer comes to the conclusion that subjects can know itself as "will". The subject and the object come together as the knowing subject.

I hope this short post will help you along your way. I am no expert in Schopenhauer, so I do not know all about his work, but it never hurts to ask. Good luck!