A few years ago, I was drawing with a 3-year-old boy. For nearly an hour, he drew concentric circles with his crayons – obsessive scribbles, really – on one half of his white page, leaving the other half blank. When I told him it was time to put the crayons away, he flew into a rage, screaming, “But I’m not finished!” Afraid that it would take another hour to complete the drawing, I hesitated before I told him to go ahead and finish the picture. Visibly relieved, he very calmly picked up a crayon and within a few seconds made a large, simple shape on the other half of the paper. “I’m done now,” he said.

Walking through the Cy Twombly retrospective of 50 years of works on paper at the Whitney Museum, I was often reminded not only of children’s drawings but of that 3-year-old boy, who could not bear to leave half his picture blank. Mr. Twombly (born 1928) often scribbles obsessively on his drawings, and also often leaves half his pictures blank. There is a kind of power in the emptiness, in the refusal to make the drawings balance and cohere. The combination of their physical resemblance to children’s art, or to the art of the insane, and their serious rejection of completeness, their commitment to the fragmentary, leaves a lingering anxiety in the work.

Mr. Twombly is a second-generation Abstract Expressionist, but he is also a Conceptualist and a Minimalist. The Abstract Expressionists embraced the mark, or “hand,” of the artist, glorifying self-expression above all else. Mr. Twombly works out of, and against, the Ab-Ex glorification of the artist’s brushstroke. He demystifies the artist’s hand by reducing it to a child’s scribble or a doodle, and he demystifies writing, or calligraphy, by making it illegible.

Mr. Twombly embraces not only the literal mark – as well as the literal word – in his paintings and drawings; he also embraces the literal emptiness, or white space, of the page, which (without formal power) often represents nothing but emptiness itself. Leaving a picture unfinished, or the meaning of words impenetrable, suggests a kind of cruelty to the act of communication. It assaults our very sense of what feels inherently right when we encounter resolution, balance, and completion.

The literal, bare-bones reduction to scribbles and fragments in Mr. Twombly’s drawings, and their dismissal of a certain level of seriousness, gives them a smug ambivalence, as if they were never intended to be drawings at all. They are often scrawled with diagrams or words (indecipherable, scribbled passages from classic texts or the titles of the drawings themselves – and this gives them the personalized, cryptic feel of diaries. The overall effect is slightly uncomfortable, even voyeuristic. It’s as if the drawings (though often very large) were blown-up visual notes, plans, secret codes meant only for the artist himself.

Such meaningless hermeticism is disappointing, because Mr. Twombly has a facility with materials. He can finesse staples, deckled edges, shadows, and bits of Scotch tape, giving them occasional weight or hints of purpose. But the drawings always seem to be more about process than their final states. There is a violence to Mr. Twombly’s drawings not only because they resist the impetus toward finish but because, in his reduction to literal rather than metaphoric language, the works insist on a cold, one-to-one, what-you-see-is what-you-get reading.

In the large “Orpheus” (1975), one white piece of paper is collaged above another. White paint is smeared on each of the pages and, in each, a brown line is scratched into the white. The lines, one above and one below, mimic one another, yet they, like Orpheus and Eurydice, remain separate and are unable to connect. The lines do nothing in terms of “drawing”: They do not open spatially, nor do they have life. They merely bite the white paint, suggesting the literal descent, ascent, and break between the two lovers.

“Orpheus” is a drawing, yet it is formally dead, it is nothing like a drawing. It has all the elements of metaphoric synthesis, and yet the lines, without any real poetic power, just lie there.

A scribble in a Twombly drawing, no matter how much energy it has, is al ways a scribble – spinning its wheels. Red in a Twombly drawing is always reduced to blood. The unreadable writing is always reduced to evasion and ambiguity. The first two works you encounter in this show as you exit the elevators are both called “Petals of Fire” (1989). Painted, and written, in red, black, and white on sheets of paper nearly 5 feet tall, they feel violent and sanguine, like blood-smeared suicide notes writ large.

“Proteus” (1984) is botanical in nature. A burst of violet and red trailing a green tail on a white ground, it feels brutal, like a freshly severed head or a bunch of flowers suddenly ripped from the earth. “Nicola’s Irises” (1990), a can-can lineup of half a dozen scrawled red and white flowers on blackened-green stems, races laterally and resembles torches or bloody clubs.

“Untitled” (2001), a mess of yellows, pinks, whites, and reds, is visceral and hot. It drips and runs and blossoms, verging toward a kind of fiery rain. “Liri” (1990) resembles a spinning torture machine. Riding on silver wheels and endlessly hammering its purple heads, it feels Medieval.

But even when Mr. Twombly’s works do have fleeting moments of beauty or loveliness – and there are a few beautiful moments in this show, which contains nearly 90 drawings and two bronze sculptures – the loveliness is felt first as unintentional and noncommittal, as a mistake, the occasional, unavoidable result of colors colliding on the page.

The drawings completed before the 1980s are pretty much all artifice – a kind of superfluous juggling of hollow marks and symbols. In some later drawings, though, Mr. Twombly can get to frenetic color notes, smudges, and smears reminiscent of Bonnard, Guston, or Joan Mitchell. At times it is almost as if – against his desire to be a conceptualist – the artist truly wants to be a painter.

There is a sly sophistication in Mr. Twombly’s kind of reduction, which chooses to ignore that great drawing exists, that in the hands of Raphael, Klee, or Matisse line has an enormous power and purpose. Whether the artist chooses to do this because he will not or cannot draw is up for grabs. I tend to believe it is a combination of both, weighed heavily by the latter.

Unfortunately, Mr. Twombly continues to have tremendous influence on a number of artists. His brand of romantic detachment and anything-goes attitude appeals to artists who would rather play with their materials than take the tradition of painting seriously. I am sure this show, which is well put together and champions Mr. Twombly’s half-attempts at resolving pictures, will spur on yet another generation obsessed, like 3-year-olds, with their own doodles and spiraling marks.

Until May 8 (945 Madison Avenue, at 75th Street, 212-570-3600).