In 1964, Life Magazine published an article about painter Roy Lichtenstein under the headline: "Is he the worst artist in America?" Today it is widely agreed that he was one of the most outstanding artists of his time.
But there is still room for disagreement about what he meant to show us.
The paintings that first made Lichtenstein famous, or infamous, look like hugely enlarged versions of comic-strip frames. When the 1960s explosion of mass-media imagery in art was first taking over galleries, Lichtenstein seemed to be applauding vulgarity.
Over the decades that followed, until Lichtenstein's death in 1997, it became apparent that his true subject was familiar images and how people viewed them.
An exhibition on Lichtenstein at the San Francisco Museum of Modern Art surveys his references to many kinds of art: the comics, classic Chinese painting, Monet's views of Rouen Cathedral, Picasso's still lifes, English romantic landscapes, and the kind of surrealist portraiture in which a face might turn into a slice of cheese.
Lichtenstein's work reminds us that artwork ranging from the most despised to the greatest has merit.
It also suggests that seeing so many pictures that they blur together as "Picasso" or "surrealism" or "Monet" affects the way we perceive art. A still life by a 17th-century Dutch master, for instance, seems at first to be derived from actual food. Less obviously, it is also derived from the tradition of still-life painting.
With the Dutch master, we may forget that our memories of many other paintings influence our experience with one particular painting; Lichtenstein tried to remind us.
Part of Lichtenstein's message is also that images, like the elements of a Christmas card, do no more than invite viewers to feel.
It is we who feel. Or, for some of us some of the time, it is we who do not.
• 'Roy Lichtenstein: All about Art' is on view at the San Francisco Museum of Modern Art through Feb. 22, 2005.