TYPED LETTER SIGNED (TLS). 2 and 1/2 pages, dated 13 July 1959, to "Dear Miss Cole," typed on plain bond paper. A substantial letter, about 1250 words, to Blish's editor at G. P. Putnam's Sons, pertaining to his "After Such Knowledge" trilogy, regarded by many critics as his most important work. Most of the letter takes up a work in progress which Blish considered a step away from the SF genre: a historical novel about Roger Bacon, here titled A LEAVEN OF POWER though ultimately published in 1964 (not by Putnam) as DOCTOR MIRABILIS, becoming the second part of the ASK trilogy. Blish, after thanking Cole for her praise of A CASE OF CONSCIENCE (the first book of that trilogy), acknowledges her advice to not mix genres, and acknowledges as well the resistance to such experimentation by both general and genre readers, but voices his dislike of these restraints. Such signals from the marketplace "further confirm my growing impatience with science fiction as such. I have been trying very hard to push back the limitations of the medium and get some things said inside it that I thought badly needed saying, but I think I have about reached the limits of this endeavor ..." After affirming the constancy of his interest in science, and the current constraints of science fiction, he glimpses a way out of this bind by turning novelistically to the history of science -- "a subject which is only very sparsely populated by novelists of any stripe." Later in the letter he voices a hope that he may be able to exploit this new subject "successfully enough to abandon science fiction as completely as I have, I think, outgrown it." Blish, rather than abandoning the field, eventually figured out how to bring DOCTOR MIRABILIS inside it. The first part of the third book of the trilogy, BLACK EASTER, appeared in 1968. Blish here is about half a decade ahead of his time. By the mid-1960s enough pressure had built up among writers of SF so as to form a New Wave that swept away many of the genre's worn-out conventions dating back to the pulp formulas of the 1930s. An important letter, not only of personal significance but of wider relevance to the history of science fiction and the connection between it and other genres, especially historical fiction. Old mailing folds, fine. (#129100).