In the month before Henry Clay Frick died in 1919, he would descend at night from his second-floor, wood-paneled bedroom to the ground floor of his Fifth Avenue mansion, which is today the Frick Collection. He would sit in the dark, ashes accumulating on his cigar, and stare at one of his many paintings, which would be lit by only a small spotlight. After a time, he would move to another masterpiece.

Was this much-hated coke-and-steel baron thinking about the money he spent amassing his renowned collection or the respect it brought him? About his industrial legacy or his reputation as a rabid anti-unionist? Or, perhaps, about the artists' intentions?

None of the above, says his great-granddaughter Martha Frick Symington Sanger. Frick, she contends in a book published last week, was contemplating moments in his life that he had marked by buying particular paintings, many relating to his beloved daughter Martha, who died at age 6 after four years of a debilitating infection. ''He was reliving his life,'' Ms. Sanger said, a life haunted by longing for Martha, whose likeness he even reproduced on his checks.

Frick's collecting, in other words, was driven by his psychology, shaped more by his grief than by his vaunted connoisseurship or need for status symbols.

Ms. Sanger's thesis stands in stark contrast to the traditional view, as stated in ''Art in the Frick Collection'' (Frick/Abrams, 1996), which emphasizes her great-grandfather's discriminating eye and credits him as the prototype for many great American collectors.

''This book breaks the rules,'' Ms. Sanger said, ''and an art historian probably couldn't write a book like this. But it makes sense to me. I'm a family member, and I didn't have academic hoops to jump through.''

Ms. Sanger, 54, does not dispute her great-grandfather's ''natural eye for beauty,'' but she says that his artworks had more important meanings, literally, emotionally and symbolically. In buying them, she said one recent day as she walked around the Frick explaining the significance off various paintings, ''he displaced his feelings for Martha.''

Her thesis, she said, springs from modern grief theory. ''When mourning is unresolved, people acquire or keep 'linking objects,' something the deceased loved or had at death,'' she explained. ''One must be open and willing to do so, but you can see that...