No such thing as a line exists in nature. It is an invention of man, the product of human perception and imagination. And yet it is one of our most basic conceptual and expressive tools, the device through which we see and experience, and then record, our simplest as well as our most sophisticated impressions, ideas, and emotions. It has challenged and fascinated such giants as Leonardo, Michelangelo, and Picasso, and has served both primitive man sketching bison on the walls of his cave, and a very young child trying to draw the family cat.
Line can do many things. It can follow and trace the extreme outer edge of things, and can turn such a weighty and complex creature as an elephant into a wondrously lumpy and curvy line. It can poke about and isolate highly complicated forms, and can transform a wild mountain landscape into a few dramatically overlapping lines. It can distill the appearance of an entire forest into a few jumbled and jagged lines, and a skyful of turbulent clouds into a series of prancing arabesques.
There is no end to what line can do. The most crucial thing about it, however , and the secret of its importance, is that it is a communicating device, a manner through which he who draws can convey to others not only what he sees and experiences, but also something of what he feels or thinks about it.
We know, in other words - and we know it immediately even if the artist has only a modicum of skill - that a particular, wondrously lumpy and curvy line represents a happy elephant, that another dramatically overlapping set of lines represents a wild mountain landscape, and that a third drawing of arabesques denotes clouds scurrying before the wind.
But that's not all. Line, in the hands of such master draftsmen as Holbein, Ingres, and Lautrec could clue the viewer into the most subtle shades and nuances of their models' character and personality. And Durer, with a slight modification of line, could differentiate between fur on a fox and fur on a lion , and indicate the approximate age of a sitter by the texture and thickness of his line. Rembrandt could dash off a simple sketch and tell us all we would want to know about a sunny landscape, a very old and bearded man, or the way the roof of a hut was thatched.
Line is versatile. It can be gentle and sensitive, and follow the contours of a form as intimately as water flowing down a hill follows every bump and crevice of its form. It can leap about like a gazelle and create fanciful elaborations on the forms of the object depicted. It can be as taut and as hard as steel wire , as nervous and hesitant as the track of a mouse, and as harsh and arbitrary as a line drawn with a ruler.
All this, line could do almost from the beginning of recorded time. With the advent of the twentieth century, however, line achieved a degree of autonomy it had never before known. Because of the greater freedom permitted artists in this century, line was increasingly seen as a component - color being another - of the abstract or nonobjective creative processes. It could be detached from its traditional role of describing things, and permitted to find and establish a life and an identity of its own. Thus, a line, rather than representing the contour of something else, could now be a line pure and simple, and nothing else. It could be curved, straight, bent, jagged, whatever, and be only that - except, of course, when it was related to other lines, and to colors, shapes, and textures to create abstract compositions.
Paul Klee wrote about ''a line going for a walk,'' with the resulting drawing consisting of tiny graphic indications of what the line had ''met'' as it wandered about its little world. He also elaborated upon the ''dialogue'' that could take place among line, color, and form. In short, Klee and many others now saw line as a separate and equal creative element, a device that could be interwoven with other elements the way the sounds of one musical instrument are interwoven with the sounds of other instruments to create music.
Line also became a major component in sculpture, most particularly in the mobiles of Alexander Calder. In these works, pieces of colored metal, wood, or tin were suspended from extended pieces of wire (which actually resembled and functioned as three-dimensional ''lines''). These twisted, dipped, swooped, and turned to create movement patterns that were linearly defined, and which could be described as drawings in space and into time.
Miro, in his paintings, used line as though it were wire or string playing games with and against bright colors and abstracted forms. And this device, toned down and made more interior and melancholy by Arshile Gorky, also lay at the heart of the paintings of some of the Abstract-Expressionists, most particularly Rothko (in his early phase), Baziotes, Gottlieb, and Motherwell. But it was Pollock who took line most to heart, and who used it most effectively to create his dense and linearly constructed ''drip'' paintings.
Line is an active thing. It can move with the speed and force of a hammerblow , and have the impact of a two-car collision (Kline). Or it can move with the darting, incisive dash of a hummingbird (Klee); the sudden swoop of a swallow (Lautrec); the thundering crash of Niagara Falls (Picasso); the subtle mysteriousness of a firefly (Graves); the lyrical grace of a butterfly (Matisse); or the inexorableness of a bullet seeking its target (Bacon).
But that is only the merest indication of what line can do, for it is as responsive and flexible as human sensibility.
No one in this century understood that better, or devoted more time to examining the almost infinite creative usages to which line can be put, than Saul Steinberg. One could almost say that he was obsessed with line and absolutely determined to probe into all its mysteries and possibilities in order to make it do things no one else had ever thought of making it do before.
Steinberg is the twentieth-century virtuoso of line, its champion and its prophet. In his hands, line creates outlandish people, cities, animals, and events with a few squiggles, dashes, or zigzags. It tells marvelous stories and makes outrageous visual puns; indicates differences in character through a choice of line; and creates wild pictorial landscapes, documents, and evidences of private musings by means of elegant Victorian curlicues, fake handwriting, fingerprints, and childlike scrawls. In one drawing, for instance, the speech of a young woman creates a flowerlike shape, while that of an older and rather pompous man becomes a solidly geometric structure. And in another drawing, the music of Verdi is represented as a flowery and linearly elegant script.
Steinberg is always full of surprises. Just when we think he has exhausted line's expressive possibilities, he comes up with a new device or a new application for an old one. Thus, between 1969 and 1971, he created a few huge ( 7 to 8 feet wide) panoramic views that incorporated literally dozens of linear devices he had invented over the years - plus a few well-placed rubber-stamp imprints. And he also found the time during those years to produce several remarkably clever tongue-in-cheek takeoffs on cubist still lifes.
Above all, Steinberg has always been very much his own man. He belongs to no movement or ''ism,'' owes very little if anything to any other artist (the one exception being Paul Klee), and subscribes to no artistic doctrine except creative watchfulness and imagination. His drawings look comfortable in both museums and magazines, and he himself straddles the worlds of cartooning and art with an ease not seen since the days of Daumier and Grosz. In short, Saul Steinberg is a wonder, and if his art isn't as ''pure'' as some might wish, it still is art in a very special and delightful way.