Sidney J. Blatt, a psychologist whose theory about the origins of depression guided treatment decisions for a generation of psychotherapists and helped deepen scientists’ appreciation of the diverse nature of chronic distress, died on May 11 in Hamden, Conn. He was 85.

Dr. Blatt was a widely published Freudian analyst at Yale in the 1970s when he began arguing in essays and scientific reports that personality developed along two intertwined pathways, one focused on identity and the other on relationships.

Disruptions in either pathway could cause identical symptoms of depression, he wrote, yet the two conditions were distinct and called for different treatment approaches. The identity-based depression — “I am a failure” — responded well to classical psychoanalysis, with the therapist as a passive listener, helping to elicit growth in an independent sense of self; the relationship-based type — “I am unlovable” — could be relieved more effectively by a more assertive therapist, guiding the formation of relationships.

Thousands of psychoanalysts integrated this theory into their practice, and its practical implications contributed to a debate about how (or if) Freud’s classic approach might be adapted for fundamentally different conditions. In the 1980s and ’90s, when tempers flared between these therapists and those who favored alternatives like medications or short-term talk therapy, Dr. Blatt emerged as a moderating influence, an easygoing presence who could move between opposing camps and integrate their ideas.

“He was like Joe Torre that way,” said Zindel Segal, a professor of psychology at the University of Toronto. “He had this ability to keep a disparate group together and focused on a common goal, which in this case was getting real clarity on these subtypes of depression.”

Productive throughout his career, Dr. Blatt published more than 200 papers and scores of monographs and books, including “Polarities of Experience” in 2008 and “The Theory and Treatment of Depression” in 2005, which he coedited. He also remained ever loyal to his Freudian roots.

He based his conclusions on case studies, observations and analyses of study data. But as a rule he avoided doing randomized clinical trials, the rigorously controlled studies considered the gold standard of evidence throughout medicine and in psychology.

“I’ve learned an enormous amount from my patients,” he said in a 2007 interview. “Therapy has been a way of being intellectually active and discovering, and at the same time caring and compassionate. I couldn’t think of a better profession.”