The first thing to be said about the unexpected death of Anne d'Harnoncourt, beyond expressing profound shock and disbelief, is that the Philadelphia Museum of Art will not be able to replace her. The museum will eventually locate a successor, but that is not the same thing.

By any measure, d'Harnoncourt was an exceptional museum director for at least two reasons - and I speak only of what I know from observation and personal contact.

Although her scholarly speciality was modernism, particularly Marcel Duchamp, she was genuinely passionate about art from all cultures, in all periods.

It might seem odd to be citing this as a virtue. Wouldn't one presume that anyone running an art museum should love art? No, because in today's bottom-line marketing culture, being an aesthete isn't necessarily a virtue.

D'Harnoncourt's enthusiasm for art produced what is for me her most significant achievement, beyond the great exhibitions the museum mounted during her tenure and the recent expansion into the Perelman Building. Because art always came first for her, she was able to maintain an exhibition standard and a philosophy of presentation that never compromised quality or pandered to commercialism.

The Art Museum has been rare among its American counterparts in presenting exhibitions that dared to challenge audiences with work by artists or cultures that were generally unfamiliar. Granted, it presented a number of Impressionist and Postimpressionist attractions during her tenure, but these were always characterized by rigorous scholarship and sophisticated presentation.

More to the point, the museum also mounted many shows of less popular art, particularly from Japan and Mexico. It abjured sensationalism - that is, art that was deliberately provocative or flamboyantly fashionable. In that sense, d'Harnoncourt preserved a museum's traditional function - to take a measured and dispassionate view of what was being created without rushing to judgment.

I applauded her for keeping the museum out of the popular-culture rat race. She achieved this because she was a connoisseur who respected the primacy of artistic values over all others. Connoisseurs are an endangered species, and as such are hard to locate. This is one reason why she can't be replaced.

The others have to do with the distinctive blend of intelligence, grace and management skills she could apply in a variety of situations, from charming a group of media people at exhibition openings to negotiating delicate loan agreements with museums around the world.

As much as she was an art historian, d'Harnoncourt was also a persuasive and effective diplomat. If she hadn't become a museum director, she would have made a splendid secretary of state.

She was the most impressive extemporaneous speaker I have encountered; I never found her at a loss for words that were not only appropriate to the occasion but eloquent as well. It's no wonder that she earned the respect and admiration of her peers across America, Europe and Asia.

D'Harnoncourt's death leaves a massive void not only at the Art Museum, and not only in Philadelphia's cultural community, but within the American and international art worlds. It's impossible to overstate her stature in all those realms. Perhaps the public at large isn't equipped to appreciate the magnitude of the loss, but certainly museum professionals, artists and critics across America are, and will continue to be, deeply saddened.

Art: Coming Sunday

Inquirer art critic Edward J. Sozanski looks back at the distinguished career of Philadelphia Museum of Art director Anne d'Harnoncourt.

Contact art critic Edward J. Sozanski at 215-854-5595 or esozanski@phillynews.com. Read his recent work at http://go.philly.com/edwardsozanski.