Abstraction
Knowledge comprehends relations between things. For this, these things have to be, in a sense, synchronously present, side by side, closely arranged. This holds even if the things are in reality separated by large distances, yes, even for events taking place at different times. All this cannot stop knowledge. It overcomes times as well as distances, it compacts, omits superfluous details and gets to the point.
This process, often called “abstraction”, appears to lead into areas lying beyond any physical reality. However, this idea itself is merely an abstraction, a picture that may depict a certain process by highlighting and strikingly illustrating one particular feature held to be essential. So here, in this case, the idea of absolute immateriality is derived from the freedom that inheres in every knowledge because of being not the hard and heavy matter itself, but its image, so to speak.
Yet, finally, every image, every representation, every form of knowledge is itself again subject to restrictions that are not less real than those of the represented thing, simply different — and therefore many of the original ones disappear.
Something, however, has to remain, a certain identicalness must exist. Image and original must allow to treat them as one and the same. The picture of a house must have enough in common with the depicted object to be itself called “house” (as in phrases like “This is our house”). Insofar it must be house.