Lori has posted an interesting question about Chapter 5 Sections 5 and 6 of PoF:

I was thinking that, if the stone had a little light on it, and was thrown in the dark, and someone filmed it, then the line would be a percept. Would it still be a concept too? Isn't a concept a relationship between things? The line is the changing relationship of the stone to its surroundings, and to the earth.

This is in reference to Steiner's comments:

...It might be quite possible for a spirit to receive the concept at the same time as, and united with, the percept. It would never occur to such a spirit that the concept did not belong to the thing. It would have to ascribe to the concept an existence indivisibly bound up with the thing.

[14] I will make myself clearer by an example. If I throw a stone horizontally through the air, I perceive it in different places one after the other. I connect these places so as to form a line. Mathematics teaches me to know various kinds of lines, one of which is the parabola. I know the parabola to be a line which is produced when a point moves according to a particular law. If I examine the conditions under which the stone thrown by me moves, I find the path traversed is identical with the line I know as a parabola. That the stone moves just in a parabola is a result of the given conditions and follows necessarily from them. The form of the parabola belongs to the whole phenomenon as much as any other feature of it does.

For me, the key part of the passage about the parabola is where Steiner then goes on to say:

The spirit described above who has no need of the detour of thinking would find itself presented not only a sequence of visual percepts at different points but, as part and parcel of these phenomena, also with the parabolic form of the path which we add to the phenomenon only by thinking.

Steiner is reminding me of the inner work I have to do to really call up the concept of a parabolic path - for it is not only a perception, it is also the thinking implied in the mathematical statement that every point on the parabola obeys the formula y=x2 (anyway that's one way of expressing it).

So I think back to my halcyon days in high school... plotting out parabolas point by point until I had enough points to sketch in a reasonable attempt at the whole of the curve.  One thing that is missing in a "mere" perception is that work of inwardly connecting one thing to another (x=1, y=1 for example), then manifesting it outwardly (draw a dot on the grid paper), then inwardly connecting again (x=2, y=4), then manifesting that (another dot) and so on.  I don't think Steiner means the spirit would perceive passively in the way we are able to (as in just staring for example) but that it would have to also inwardly participate in the actual realisation of the concept parabola in a particular case. 

I connect this with the later part of this passage where Steiner says:

If our existence were so linked up with the things that every occurrence in the world were at the same time also an occurrence in us, the distinction between ourselves and the things would not exist. But then there would be no separate things at all for us. All occurrences would pass continuously one into the other. The cosmos would be a unity and a whole, complete in itself. The stream of events would nowhere be interrupted.

This sounds very much like Steiner's much later descriptions of how elemental beings, members of the spiritual hierarchies and so on participate in the being of the cosmos...  not incarnated physically in the same sense that human beings are, but nevertheless participating in the essence of things as they actually are.  And also his description of how our own experience of the cosmos and of the beings around us is completely changed between death and a new birth, and during sleep every night.