“The shift in values from the painting as object, as it had been seen by the Cubists, to the painting as a moral undertaking was radical and extensive.”

Dore Ashton wrote these words about the Abstract Expressionists, but their redefinition of “painting as a moral undertaking” might as well have been a personal credo.

Fittingly, they’re from A Critical Study of Philip Guston (published in 1976 by the University of California Press and republished the same year by Viking under the title Yes, but…). It was the first book to treat Guston’s late-1960s apostasy from abstraction to satirical figuration with the depth of research, insight, and seriousness it deserved.

I had the privilege of knowing Dore Ashton for more than 20 years. Our friendship stood on that vague threshold between the professional and the personal; nevertheless, she would freely share her enthusiasms, proclamations, and antagonisms with me. I never knew her to hold anything back.

When Dore passed away on Monday, one of the last great oaks of American art criticism fell. Her writing career spanned the 1950s to the middle of the current decade, with more than thirty books and countless exhibition catalogues, magazine articles, and newspaper reviews to her credit. As a teacher she has influenced generation upon generation of young artists, many citing her class as the one that opened their eyes to the meaning of art.

The contours of her life are well documented and can be found elsewhere. The Dore Ashton I knew was someone who was always on alert, always engaged, always seeking out the new and daring. Unlike other writers to emerge from the grand American experiment of Abstract Expressionism, most notably Clement Greenberg, she never attempted to prescribe what art should become. She knew that it was a fleet-footed chameleon, as manifested by her subsequent advocacy of artists as diverse as Hiroshi Teshigahara, Alfredo Jaar, and John Walker.

I once asked her if she was at least a little dismayed when she walked into Guston’s Woodstock studio and discovered that he had been making small, cartoonish paintings of bricks, light bulbs, shoes, and hooded Klansmen. She said no — Guston was an intelligent artist, and she believed that she should go where he wanted to take her.

Her openness, however, was coupled with a fierce intolerance of mediocrity in all of its forms. She decried the influence of the marketplace on contemporary art and rejected academicism in art writing. Her critical style is as immersed in literature as it is in philosophy — an encyclopedic range of historical allusions, personal experience, and deep reading, which she expressed with elegance, simplicity, and force.

Politically, she was a leftist’s leftist, the patron saint of lost causes. The last time I visited her, a snapshot of Alger Hiss was resting on her kitchen table, taken after his release from prison. If you were her friend, she would stick by you even if, like Guston, like Hiss, the whole world turned against you. Or perhaps I should say, especially when the whole world turned against you.

Our perception of the immediate postwar era is unavoidably shaped by “The Irascibles,” the myth-making, much-imitated group portrait of the Abstract Expressionists taken by photographer Nina Leen and published in the January 15, 1951, issue of Life Magazine.

(The photo was actually captioned “Irascible Group of Advanced Artists Led Fight Against Show,” referring to a contemporary painting competition sponsored by the Metropolitan Museum of Art, which excluded every member of the group.)

With her hard-charging, unshakable sense of justice, Dore could have very well been called the Last Irascible, but she would have laughed it off. She was too self-deprecating, charming, and funny to be typecast. What mattered most to her was the morality of an action, no matter what domain of life it affected.

I can only imagine what Dore would have said about the onset of the Trump era, a rupture in the fabric of national identity that fulfills many of the alarms she had been ringing for decades. As the peril increases by the day, she will be missed for her righteousness and clarity of thought as much as her humanity and humanism.

But her writing — springing from the richest veins of world culture and enraptured with epiphanies of beauty — will remain as a rebuke to the lies, violence, greed, and coarseness of the charlatans, hypocrites, quislings, and fools now luxuriating in their orgiastic power-grab. And for this, at the very least, we’re indebted to her vision, idealism, and example.

Thomas Micchelli is an artist and writer.