Picasso's early drawings, at the Frick in NY

What Matisse was to color in 20th-Century art, Picasso was to line. Not that Picasso wasn't a superb colorist, but his every work started with a charged volumetric field defined by line. Unsurprisingly, then, Picasso's graphic work was not only a large part of his enormous output, but also a critical component of it.

His etchings—for example, the Vollard Suite—are well known, but his drawings less so. Yet it's in the drawings that his overall evolution as an artist can best be seen, and where some of his greatest achievement lies.

Drawings are to an artist what the piano is to a composer: both a place to sketch out work intended for another medium and a medium itself for finished work. The distinction between these two functions isn't easy to make, for a quick sketch can be a perfectly realized work of art, and the question of "completion" is, particularly in modern art, problematic. Painters often leave sections of their canvas bare, or images deliberately truncated.

This sensibility derives, I think, from the Renaissance and Romantic construction of the ruin as a shorthand symbol of temporal passage, lost heritage and encroaching mortality. That, in turn, relates to the structural uncertainties of modern physics and chaos theory, and to the general suspicion of closure which they've encouraged in the arts generally. The drawing, which can consist largely of blank space, is ideally suited to express these attitudes— less is more, and least is often best.

The unseen horse

One of the works in the Frick Collection's superb show of early Picasso drawings makes this point handsomely. It shows a nude male rider on horseback, seen from the rear. The horse isn't drawn at all, but inferred from the way the man's outstretched legs and buttocks cover the sheet, and by the erect posture of the head and back: He can't be anywhere but astride a horse, his carriage and attitude reflecting not only that fact, but also the combination of command and exposure (the legs splayed, the genitals resting on the animal) that defines the relationship of a human rider to his mount.

Because the horse has no defining shape or limit but the rider's legs, the entire sheet is suffused with its power, an invisible presence that leads back to that of the artist himself. The rider may or may not be a self-portrait, but he is a self-projection, and the command he exerts over the pictorial space is certainly that of Picasso himself.

Youth on Horseback is, by any aesthetic criterion, a fully realized work of art. But is it a complete one— complete in the sense of representing the artist's final, deliberate intention to say just so much in just this way, and no more?

Adding by subtraction

A similar work by Degas, who favored such equestrian subjects, would certainly be fuller, even if it did not represent the whole of the horse or fully model it. Picasso adds by subtraction, and makes negative space perform expressive function. That is genius.

But can we be sure that he didn't simply leave a half-finished sketch that draws the viewer's eye and imagination to complete it— in short, that the viewer himself doesn't collaborate in creating what he perceives as the realized artwork?

Or could it be that Picasso does not merely invite us to finish his work, but expects and in some sense demands that we do so? And is this, then, not a new kind of art-making itself?

Drawings lend themselves to this kind of ambiguity, and to some degree they always have. Modern art in general demands more and more of the viewer, not so much in deciphering content as in supplying it.

Picasso's radical simplification of his art in the early 1900s, particularly evident in the drawings where color and shading are dispensed with and only line remains, insists that we bring to it what he has left absent— or learn to content ourselves with the famished repast he offers.

Nudity vs. nakedness

It's no accident that Picasso is attracted in this period to gaunt and even starving figures, or gives us not nudity but nakedness. It's only a short (although an immensely difficult) step to abandoning illusionistic or representative art altogether, and inventing an entirely new language that will make demands of the viewer such as were never made before: Cubism.

The Frick show enables us to follow this progression, from the astonishingly talented academic drawings of Picasso's youth and adolescence, to the expressive simplifications of his exploration of the Barcelona and Paris demimonde and the experiments that led to the Cubist style. In Picasso's hands, Cubism was a surgical knife that exposed primary forms, while at the same time building structures of architectonic complexity.

Pure abstraction seemed the next step— a step Picasso's slightly older contemporary Kasimir Malevich would take. But Picasso himself never abandoned the image, however he might veil, dissect or expressively distort it.

No place for sentiment

By the mid-1910s, he had startlingly returned to line portraits whose meticulous clarity of representation recalled the mastery of Ingres. One of these portraits, a part of this show, was of Igor Stravinsky, whose own art was experiencing a similar phase of neoclassicism.

Personality certainly comes through in these works, but sentiment is rigorously excluded: The attempt to evoke psychic disturbance and trauma in the work of a Munch or a Kirchner holds no interest for Picasso, at least in this period, and still less do Kandinsky's efforts to directly depict emotional states.

At the same time, however, Picasso offers no retreat from the high ground of modernism, but rather a distilled quality that would have been impossible to the 19th Century.

Picasso, like Braque, would never return to the analytic Cubism in which objects, fractured into planes, became virtually unrecognizable. This style had produced some of the most luminous works of the 20th Century, but both men would abandon it after two years, almost on cue.

Monumental women

Cubism would however remain a permanent part of Picasso's arsenal, as a particularly fine example— Still Life in Front of a Window at Saint Raphael (1919)— reminds us here. Using only pencil and gouache, he presents a setting as richly rendered and fully textured as any oil painting.

As Picasso approached his 40th birthday in 1921— the exhibition's cut-off point—he became interested in monumental portraits of women, works whose rounding and modeling were in the greatest possible contrast to the angular nudes whose gradual deconstruction had led him into Cubism a decade earlier. The viewer is left to wonder: "What next?", although of course we have the answer in the severely geometrized shapes and figures that soon emerged in the Paris and Dinard sketchbooks.

Fifty years later, "What next?" would still have been a plausible question to ask of an artist who, perhaps more than any other, never ceased to surprise.