in Chapter 5 Steiner is "Hunting the Snark" to borrow a phrase from Lewis Carroll.  He is hunting down the "thing in itself", the objective world which supposedly exists independently of any element of thought or inwardness. 

And he is merciless in his pursuit.  Where most thinkers might stop after a few observations about the nature of subject and object, perception and so on, Steiner pushes us to keep thinking right through to the end, not to stop halfway and lazily think that "something out there" happens from there onwards.

For example, Steiner talks about the perception of red. 

Let us assume that a certain perception, for example, red, appears in my consciousness.

For many thinkers this would be enough.  From here, they will start making abstract generalisations about the nature of perception and its relation to consciousness, the supposed nature of objective reality and so on.  But not Steiner - he continues:

To continued observation, this percept shows itself to be connected with other percepts, for example, a definite figure and with certain temperature- and touch-percepts. This combination I call an object belonging to the sense-perceptible world.

It's easy to follow him to this point.  Perhaps it's a piece of hot iron glowing red.  We are not so abstract now, we have to imagine to ourselves how red appears to us in a real situation.  From here we could start talking abstractly, for example, about how the real world is not composed of separate qualities like "red", "hot" etc. but presents itself to us as a conglomerate of all of these.  But Steiner still doesn't stop here:

I can now ask myself: Over and above the percepts just mentioned, what else is there in the section of space in which they appear? I shall then find mechanical, chemical and other processes in that section of space.

Fair enough, that is very scientific.  From here, it's possible to assert things like "well, the piece of hot iron is really a collection of imperceptible atoms constantly interacting according to certain laws".  We know that experiments can be carried out to measure these processes he's talking about.  That just provides additional proof that the "real" nature of the world is the one described by conventional science - force and matter.  But still he doesn't stop:

I next go further and study the processes I find on the way from the object to my sense organs. I can find movements in an elastic medium, which by their very nature have not the slightest thing in common with the percepts from which I started.

Still very scientific.  Of course, if we want to make assertions about the nature of perceptions it is sensible to investigate the physical conditions within which they arise.  So if there are visual perceptions we find electromagnetic waves between our eye and the object, if there are sound perceptions we can measure sound waves in the air, and so on.

But Steiner now adds an important observation on the progress of this train of thought "...which by their very nature have not the slightest thing in common with the percepts from which I started".  This can make me start to think for myself "well, does this all make sense?  Does the scientific investigation of totally different percepts using totally different concepts really prove that my starting point (the percept of red) is not real, is only subjective?  Is the percept "red" really less valid than the percept "reading on light detector" for example?  They are both percepts, and thinking joins concepts to both of them to achieve knowledge in their respective contexts.  And still Steiner does not give up:

I get the same result when I go on and examine the transmission from sense organs to brain.

He wishes us to think the whole thing through for ourselves, right to the end.  It is all too easy to stop at one of the above points and not realise that at every step we still have to apply thinking to join the polarities of concept and percept - there is no reality "out there" that is beyond this. 

Once we realise there is no reality "out there" the way is open for a very great deal in understanding the true significance of our inner life...