REBORN (2008), THE FIRST volume of Susan Sontag's journals and notebooks, took her from precocious teenager to the brink of massive success — her publication of the essay "Notes on Camp" in 1964 — and documented her intellectual and sexual awakenings. There, we meet Sontag in 1947, aged 14, declaring, "I believe that the only difference between human beings is intelligence." We witness her acute mind develop through traditional education (perfunctorily at North Hollywood High School, more rigorously at UC Berkeley, and, most thrillingly, at the University of Chicago) and through the experiences of a teenager and a young woman willing her life to happen.

That Sontag happens to be bisexual affects her narrative of self-fashioning, but does not determine it. As early as age 15 she confesses to feeling she has "lesbian tendencies," yet it is an element of her identity rather than its centerpiece: one of the fragments that add up to make the whole person, as important as the many lists she makes of books to be read or films watched. In Reborn we observe a persona developing, but we also read about a person growing up: seething with ambition, falling in and out of love, and making some questionable life choices (like marrying her professor at U of C, Freud scholar Phillip Rieff, at age 17). The volume's last line, written while on her own with her young son David in New York City, she formulates the equation that sums up what she has learned: "Intellectual 'wanting' like sexual wanting."

Both Reborn and the second volume of Sontag's journals and notebooks were edited by Sontag's son, David Rieff, and in the introduction to the former we get the requisite hand-wringing about publishing documents so resolutely personal. Sontag never told Rieff what she wanted to do with the notebooks, but she did sell them to UCLA, along with her other papers, and did not restrict access to them in any way. Rieff, nevertheless, feels guilty unleashing his mother's secrets and judgments onto the world. "In particular, she avoided to the extent she could, without denying it, any discussion of her own homosexuality or any acknowledgement of her own ambition," Rieff writes in the introduction to Reborn. Yet these are major themes of the journals, as they were of his mother's life.

In his introduction to the awkwardly titled As Consciousness Is Harnessed to Flesh: Journals and Notebooks 1964-1980, Rieff tells us that Sontag "toyed desultorily with the idea of writing" an autobiography in the early 1990s, which surprised him, given her characteristic skepticism about self-exposure. "To write mainly about myself," Sontag said in a 1972 interview, "seems to me a rather indirect route to what I have to write about." Rieff does, however, raise the specter of autobiography (he calls them "first and foremost acts of homage") in some of Sontag's more valedictory essays, particularly the ones on Elias Canetti and Walter Benjamin ("Mind as Passion" and "Under the Sign of Saturn," 1980, respectively, both collected in Under the Sign of Saturn).

This attitude toward autobiography as only an "indirect route" to her true subject captures the spirit of Sontag's work, though Rieff is onto something when he cites the Canetti and Benjamin essays as being particularly close to Sontag's own consciousness. (She even notes that she, like Benjamin, is "Saturnine," that is, literally born under the sign of...