For some, Jews play the same psychological function as goblins, said New York psychoanalyst Mortimer Ostow.

Ostow drew that conclusion in a lecture on Tuesday of last week, "Myth and Madness: The Psychodynamics of anti-Semitism," part of the International Psychoanalytical Association's 39th Congress. He delivered the lecture, an abstract of his new book of the same title, to 250 analysts who were among 2,400 colleagues from around the world gathered in San Francisco's Marriott Hotel.

As long ago as the Middle Ages, "devils, demons and Satan were sources of evil" just as Jews were, he said. A superstitious European populace believed those nasty creatures were Jews' friends and allies.

"That's why Jews were often depicted with horns and a tail."

Ostow, professor emeritus at New York's Jewish Theological Seminary, explained how apocryphal tales pinpointing Jews as evil sorcerers, child-killers and plague-fuelers serve the same function as other myths: They satisfy a human need for causality, for explaining a perplexing aspect of the world.

"We have so little control over the misery that arises inside of us [that] we look for external sources of evil. As a defense against pain, [evil] is attributed to an outside source," Ostow said. And Jews — more tangible than demons — made even better targets, he said.

In an hourlong talk, Ostow explained the origins of various negative myths about Jews. He included Christian Bible references to Jews' disloyalty, dishonesty and untrustworthiness. This ancient depiction of Jews as poisonous "serpents and vipers" was intensified by what Ostow calls a "sibling rivalry" between Jews who stayed Jewish and those who converted to Christianity.

Early Christians, he said, sought "validation from the Jews, but were rejected," and this withdrawal of psychological support made the converts resentful.

Over the centuries leading up to the Middle Ages, this rivalry — and the anti-Jewish furor it evoked — grew more active and more lethal, he explained.

In the year 1137 in Lincoln, England, a group of British Jewish youths was accused of torturing, crucifying and murdering a Christian boy, dubbed "St. William." By 1348, legions of Europeans were blaming Jews for the bubonic plague. Thousands of Jews were massacred, ostensibly to avenge plague victims.

"A satisfactory explanation was there," Ostow noted, since Europeans knew viral contagion, not Jews' machinations, spread the plague. "But the community required more," he said.

As Jews' status fell, their employment options shrank, leaving them with no choice but to work as money-lenders. Soon enough, they were blamed for their clients' financial woes. Echoing other historians, Ostow explained that thus was born the persistent myth depicting Jews as powerful, dangerous and greedy — qualities manifest in Shakespeare's infamous Jewish character, Shylock, in "The Merchant of Venice."

Those stereotypes were implausible, as European Jewish communities were marked by "poverty and lack of power." Lacking visible proof, anti-Semites posited that Jews' evil work was done covertly. In anti-Semitic literature, the stereotype of Jews' secrecy and conspiracies buttressed existing negative beliefs.

Anti-Semitic literature has not changed much, Ostow maintains. From the notorious "Protocols of the Elders of Zion" to Hitler's "Mein Kampf" to Pat Robertson's recent work, "The Myth of the New World Order," such literature is rife with conspiracy theories.

While studying modern anti-Semitism, Ostow found that in order for these myths to persist, their perpetrators must adopt such attitudes in childhood.

As part of a 1981 research project conducted by the Psychoanalytic Research and Development Fund, of which Ostow is president, 15 analysts studied 19 psychiatric patients, and found that most anti-Semitic subjects alluded to these myths, learned at a young age and validated by adults.

They also found that the more repressed and hostile a patient was in general, the more intensely anti-Semitic he or she was.

Ostow, now an attending physician at the Montefiore Medical Center in New York, explained that his patients' anti-Semitism is also often phasic — that is, it alternates with philo-Semitism, a strong affinity for Jews.

Most of the subjects who harbored anti-Jewish prejudices evinced that they had once "idealized Jewish friends," Ostrow recalled, "until an adverse incident caused a retreat." Among history's phasic anti-Semites, he counts both Martin Luther and Mohammed.