'Matisse loved moving paint around. Picasso loved to draw," Kenneth Noland pronounced, some years ago, as we walked through an exhibition devoted to the two modernist giants. His assessment of the Spanish master's preference is borne out by "Picasso's Drawings, 1890-1921: Reinventing Tradition," now at the Frick Collection. Organized by Susan Grace Galassi, the Frick's senior curator, with the Picasso authority Marilyn McCully and Andrew Robison, senior curator of prints and drawings at the National Gallery of Art, the show documents the first three decades of Picasso's life as an artist with more than 60 works on paper. They range from austere pencil or pen-and-ink drawings to opulent watercolors, gouaches and pastels. Beginning with an endearingly awkward but impressive rendering of a statuette in the Ruiz y Picasso family apartment by the 9-year-old Pablo and ending with a group of authoritative heads of pneumatic goddesses in modish, flower-bedecked hats by the acclaimed 40-year-old modern master, the instructive selection mixes well-known emblems of Picasso's achievement with seldom seen, often revealing examples, many of them from private collections. The result is an incisive portrait of a restless artist for whom the act of drawing could be a way of thinking, exploring, possessing, flattering, ridiculing, experimenting, rendering homage, challenging, or inventing—sometimes all at once. Meticulous studies of a cast of a Parthenon sculpture and a sturdy male model, along with a vivid head of the artist's father, bear witness to Picasso's mastery of traditional techniques by the age of 16 or 17. Yet an energetically stroked portrait of a young male friend, made in Barcelona only a year or two later, announces that the artist quickly rejected academic values for a bolder, more expressive, more forward-looking attack. And the dark-eyed, 20-year-old dandy staring from a self-portrait made in Paris in late 1901 or early 1902 may have correctly center-parted hair and an elegant blue striped cravat, but he looks truculent and determined. Yet the pastels and drawings from the Blue and Rose periods that follow, meditations on poverty and the lives of saltimbanques and harlequins, show the young Picasso exploiting his achingly sensitive touch in images that verge on the sentimental. A 1904 sheet of a young woman holding her infant amid studies of hands is redeemed, however, by the wrenched pose and direct, delicate line. The installation's unexpected pairing of a poetic view of a slender, nude "Youth on Horseback" (winter, 1905-06)—a back view, all suave modeling and subtly indicated musculature—with a page of fiercely outlined, summarily brushed, aggressively frontal female nudes made less than a year later dramatizes Picasso's shocking refutation of his astonishing skill in a quest for intensity and immediacy. The simplified heads and thickset, burgeoning bodies of the women reflect his enthusiasm for ancient Iberian sculptures, seen in Spain. But these chunky, rock-solid figures make us look back to an earlier drawing on an adjoining wall, a seemingly modest effort that takes on new significance in relation to the hardened forms and incipient geometry of the hefty 1906 figures; made as an homage to Gauguin, in 1902, the robust standing nude not only echoes that artist's monumental Tahitian vahines, but also seems to prefigure Picasso's massive women. Nothing about this ambitious young Spaniard is simple. The exhibition's early Cubist drawings and watercolors—1907-1913—are a high point. They offer testimony to the impact that the great 1907 Cézanne memorial exhibition—organized to honor the painter, who had died the previous year—had on the 26-year-old Picasso, as on most of his colleagues. We watch him transform the implications of Paul Cézanne's hard-won, carefully adjusted touches into an evocative language of planes, strokes and angles in landscapes, figure studies, heads, a knock-out still life of a chocolate pot with the presence of one of the Demoiselles d'Avignon, and a pair of stunning watercolors of bathers in a forest. Some works deploy detached touches, others use dense, faceted forms, like surrogate sculptures, and others are fragile constellations of floating lines and scribbled patches. Academic values still reverberate in the nuanced indications of planes, but all traces of sentiment and virtuosity have been subsumed by formal rigor. Yet Picasso was an unstoppable shape-changer, especially during the vital years under review at the Frick. His prodigious inventiveness and his refusal to settle for a single visual language are attested to by the range of the exhibition's works from 1914 to 1921. Nearly abstract, sharp-edged figures constructed with crisp planes coexist with hybrid Cubist-naturalist echoes of Cézanne and intently observed, exquisitely controlled pencil portraits that deliberately invoke Jean Auguste Dominique Ingres. An energetic, parodic drawing of dancers based on a celebrated print from the Romantic Ballet era encapsulates, along with a witty drawing of Igor Stravinsky, Picasso's association with Sergei Diaghilev and his experimental Ballets Russes. The exhibition ends with overscaled, elegantly modeled drawings of buxom women that propose yet another direction, a wholehearted neo-classicism that fuses Picasso's academic heritage with his rebellious modernism. An amply proportioned, headless torso in modern dress, in the Frick's lower-level temporary exhibition galleries, prepares us for the coda, installed upstairs: a group of full-cheeked, enigmatic heads, modern-day sisters of the Museum of Modern Art's three classically garbed goddesses at a fountain. Implacable and massive, they seem utterly passive, as if they aspired to the condition of antique sculpture—"reinventing tradition," as the exhibition's title has it, indeed. Ms. Wilkin writes about art for the Journal.