The other element in the painter's work, line, also played a significant part in the examination and reflection of the abstract artists in the first two decades of the twentieth century. To be sure, in purely quantitative terms line seems to have attracted less of their attention than color. Thus, while in On the Spiritual in Art Kandinsky devoted a whole chapter specifically to the “Effects of Color,” he treated line mainly in a chapter called “The Language of Forms and Colors.” Even in this chapter the main parts were, in fact, devoted to color rather than to line. As we shall see, a similar situation also obtains in the theoretical texts composed by Mondrian at this period. Evidently, the founders of abstract painting considered color as the more interesting, and in their specific context also the more important, feature of the two. Yet while they may in fact have devoted more intellectual effort to color, line was and remained a crucial problem for them. Understanding line was of the utmost urgency in the formulation of a theory of abstract painting. In this chapter I shall try to show that in fact line, rather than color, was a touchstone for the validity of “abstraction,” as they understood it, in painting.
The specific question that arises here is easily seen. The conceptual upheaval in the doctrine of art brought about by the school of abstract painting affected the function of line perhaps more profoundly than any other basic element in the painter's craft. As noted in the previous chapter, for centuries line was considered the main foundation of the art of painting. The principal reason for this high regard was the assumption that line determined the general arrangement of figures and masses within the space of a painting. Line was thus the primary means by which composition, that is, the overall arrangement of the painting, was achieved.
The function of line as making composition possible and serving as its foundation is, however, inseparably linked with the traditional view of what art is, and what a picture should be. Line was essentially understood as the outline, the contour, or contorno in the language of the Renaissance