We can look at it like this: we go a step further with our instant reaction to the word "tram" and retain only the colors; then, since the colors must have a shape, we put them down as square patches. We have continued our selection of impressions by eliminating all but the colors seen, which, although reduced to unmodulated patches, still have a relation to the objects. Blue and yellow can be expressed only by blue and yellow colors. If we were to put red, say, for yellow, and brown for blue, it would no longer be an abstraction, but just insanity.
If we study the reproduction of Klee's Resonance of Southern Flora, it is clear (with help from the title) that he made a selection on the basis of color, until nothing further could be transposed. The individual forms of the vegetation, unessential to the general impression, have been abstracted into a scheme of squares.
Let us imagine an ordinary brown enamelled milk jug. Milk is poured in and out of it. The milk flows into it in a line, spreads over the bottom of the jug, rises up and splashes out of the spout at the top. This we are doing, let us say, in a green tiled kitchen. We see the colors of the milk: yellowish and bluish. All this we see together at once, but this vision, although deriving from a naturalistic scene, is as illogical as the colors of numbers. It is this illogical, but clearly sensed "seeing" that we reproduce in a picture.
In this example the author confined himself to noting down what he "saw" with his eyes closed. He named the colors of the natural surroundings in order to show how much had vanished in his interior sight, although what remains is in accord with the color seen with the open eye. It is possible to give here an impression of the process in time, which can never be done in an objective picture. A single picture can give what a filmstrip has to render in a series; here the author gave the idea of a milk jug with a linear representation. There are many other possibilities for the student to try!
The impression could be reproduced, for instance, by color alone, without any clear, formal outline, for liquid has no definable shape, but depends on other factors: falling through the air it takes on a drop shape; on a surface it spreads out as far as its consistency and the nature of the surface allow; in a vessel it takes the shape of the hollow. The idea of milk can be expressed in color in any of these shapes, since it can take any of them. "Milk jug," on the other hand, is something different, for its form, color, and use are inseparable from it.
This simple example has been chosen deliberately to give an idea of the process involved in an abstraction. We also started out from an object, a tangible material, for how would it be possible to explain how to arrive at an abstraction taking as an example something like the working out of the concept "medieval poetry"? However, even a series of words only half understood
(unless by chance our student is versed in Anglo-Saxon or Norman French) can leave an impression of shapes or colors. That, however, is an entirely subjective affair, tot homines.
The second example begins with quite an ordinary acoustical experience, independent of any external natural forms or color impressions: rain falling on a roof at night. The author had here no need to investigate his "vision"; it came to him repeatedly on its own, and he noted it down as something valid only to himself which might one day be worked up into something.