"Zero to Infinity: Arte Povera 1962-1972," which toured to the Smithsonian's Hirshhorn Museum this fall and runs for a few weeks into the new year, is one of the best and most enjoyable art exhibitions I've ever seen. From what I've been able to gather, a broad range of other viewers -- from security guards to teenagers to arty office workers -- seems also to have come away with similar goodwill toward the Hirshhorn show, and toward the 14 Italian avant-gardists that it surveyed. But what is most pleasing about the exhibition, and what may make it especially significant, is that I'm not sure I or most of my fellow visitors would always have found it such easy going.

A meter-square gray cube, made of mirrors lashed together with their polished sides facing in, as a kind of thought experiment in infinite regress.

A two-person breakfast nook, of sorts, cobbled together from rough-cut planks, so that it hovers between rugged minimalist sculpture and usable furniture.

A slide projector shining into empty space, casting the single Italian word "visibile" onto the clothing of unwitting passersby: The invisible paradoxically made distinctly visible, if only for an instant and with the help of bystanders.

Twenty years ago, maybe even 15, the strongly conceptual component in these and other pieces at the Hirshhorn show might have seemed hard work -- worthwhile, maybe, but more like necessary medicine than a pleasant treat. In classic conceptual art, novel ideas for ways of making viewers think and feel were seen as crucial -- as important as the objects that might derive from those ideas. (Sometimes, ideas that could not be given any concrete form at all were especially favored, as a guaranteed escape from the sullying, commodifying forces of the art market.) This once left viewers raised on simply fascinating things feeling baffled and dissatisfied. Now, however, it seems entirely natural to look for conscious thought, and then its bold materialization in an artistic medium, as at the heart of recent art.

One reason for the new appeal of the conceptual in art is that there's been time, over the past four decades, to whittle things down to just the best examples. The Italian Arte Povera movement, for instance, represents an early high point in the genre, and the Hirshhorn show managed to cull from it just the pieces where it got things right. Which means that, in most of the works on view, the marriage between initial idea and finished object is particularly tight. That cubic mirror box, for instance, doesn't just illustrate a written-out abstract idea that would speak as well on its own; it truly puts the idea of infinitude into a powerful material form.

Looking back over the history of conceptually driven art, I think we've also come to realize how material and visual it always was. In the 1960s, when the idea of an art of pure ideas was young, audiences tended to dwell on the novel "conceptual" component of the work, and tended to scant the "art" part that was always there. With hindsight, we can realize that what a conceptual work looked like has almost always mattered more than anyone let on. Even apparently hard-nosed conceptualists like Lawrence Weiner (best known for cryptic texts that he gets written in big letters across the gallery wall) or On Kawara (a typical work consists of piles of loose-leaf binders that record 1 million years' worth of dates) produced pared-down, minimal objects and installations that functioned as elegant, very visual art even as they conveyed ideas.

We've also come to realize that the ideas behind conceptual art were often softer, more intuitive, less threatening than at first they seemed; they were more like the informal little notions that got traditional art objects off the ground than like the ordered propositions of a philosopher or physicist. They were little ideas from which artmaking could take off, as much as they were full-blown concepts needing visual elucidation or polemically resisting it.

Even as the concepts of conceptual art stopped seeming so imposing, classical abstraction, and its insistence on the virtues of pure visual sensation, began to lose its sway. Frank Stella's famous dictum "What you see is what you see" -- the idea that the essence of a work of art should be visible right on its surface -- was replaced with the idea that there is nothing wrong about an art object that requires a touch of outside information to help it do its work. A label on which the artist tells you that a big gray box is in fact made out of mirrors doesn't necessarily betray the essences of visual art. There's nothing wrong in needing a tip-off from a museum guard to notice that a seemingly pointless slide projector in fact is shining content onto you. Thoughts and words and the concrete media of art, if carefully assembled by the artist into a strong package, can work together as a potent unit.

But maybe the true reason for the new ease we seem to have with the conceptual in art is more straightforward than all these explanations might suggest. Visual art functions much like other kinds of human language and communication. When a community comes up with a new dialect, or history spits out a whole new way of speaking, it can take some time for outsiders to begin to understand what's being said. James McNeil Whistler's mild-mannered impressionism was once derided as a pot of paint thrown in the public's face; now even the much tougher, more radical pictures of his contemporaries Edouard Manet or Edgar Degas draw crowds who want an easy day in a museum. Picasso's works were once attacked as meaningless gibberish whose only point was shock; now they sell as pretty posters by the thousands. Forty years after the radical conceptualists of Arte Povera came on the scene, we may at last be tuning in, with simple delight, to all the things they've always had to say. It's just taken us a bit of time to clue-in to their accent.

Michelangelo Pistoletto's breakfast nook deserves a toast.Seeing is believing with Giovanni Anselmo's "Invisibile."