Everything which can be seen or touched is originally experienced as something plastic in space. If you wish to formulate the experience of these two senses for yourself, or to communicate it to others, you note down what you have seen; you draw points, lines, and areas in contrasting colors onto a flat surface. The image thus created gives an illusion reproducing the experience; it may be stronger or weaker than or equal in force to the original experience, according to your ability and to the material you use.
The most direct representation of volume is, of course, sculpture, or modeling in three dimensions. A sphere can be held, whereas a drawn circle representing a sphere cannot. Thus, the picture is an illusion, which in life is often much more significant than what is easily tangible. But even sculpture can show only volume, not space. If the object represented is significant and expressive only by its position in space relative to other objects, then a sculpture of it is no more complete than a drawing.
The desire to formulate and to communicate an experience is as old as humanity itself. It may even be that drawing and modeling are older than the spoken word, in any event older than poetry. It is conceivable that before the perishable word there was the picture, the drawing, by which even the mute can express himself. Things which are hardly describable in words at all can be understood at a glance from a picture, although, conversely, words can describe feelings which cannot be expressed pictorially except in abstract pictures.
This aside, a verbal description of an experience is always much more related to consciousness and the intellect than the pictorial description, which achieves its strongest impact when dealing with visions and ideas not explicable by logical formulation. This "inner" vision may be so strong that it can be reproduced as directly as something which is objectively present to the sight.
The vision, on the other hand, may detach itself completely from the memory of recognizable objects, abstracting from the external form, which is universally recognizable at all times, inner, subjective processes and reactions which are actually unreal and do not correspond to a common vision or feeling.
These abstract representations may thus not be universally comprehensible; then words and explanations are again needed to guide the response of the beholder to the point from which the painter started. Without them, quite contradictory interpretations can be read into abstract pictures, as in a game of ink-blot reading. Properly, a picture should need no captions; its true nature is to create an unequivocal effect without words.
The first efforts of human beings to set down pictorially the visible and tangible world were aimed at achieving the closest imitation of the object with means precluding any misunderstanding or ambiguity. The most unequivocal of these means is an area of color.
If a child is given the most varied materials for drawing and painting, he will always choose color and make colored areas. The image on the retina of the human eye is composed of these colored areas. The lines which we think we see are only the boundaries we feel between two colors. This would not need saying if we were not educated (or miseducated from childhood by the example of others and by our own efforts to set down everything we see primarily as outlines.