If solid evidence reveals that major, long-held beliefs rest on wobbly pillars of false assumptions, how can we convince others to jettison such beliefs and embrace novel approaches? What can we learn from the tragic case of Ignaz Semmelweis in this regard?

In 1847, one in six mothers perished from childbed (puerperal) fever at the Vienna General Hospital where Dr. Semmelweis worked. In some months up to 30 percent of mothers died during the postpartum period. With obsessive focus, he sought the cause of this deadly illness. Based on keen clinical observation, numerous hours of autopsy work, and incisive logic, he reached the conclusion that “cadaverous particles” were being transferred by doctors performing autopsies to the women whose babies they delivered later in the morning. Furthermore, he implemented an effective disinfection routine with a chlorinated lime solution, which resulted in plummeting death rates.

This combination of astute clinical insights along with a remarkably effective intervention to prevent these tragically common deaths of young mothers should, ostensibly, have led to rapid adoption of his disinfection protocol by all physicians. Instead, his innovative, lifesaving approach was not widely accepted until years after his death in an insane asylum.

In a completely rational world, one would merely present objective evidence, which would be assessed by others for its reliability based on such factors as the methodology, strength of the findings, potential confounding factors, and generalizability. In this scenario, once rational peers had judged the evidence to be adequately robust, they would accept the conclusion and reject unsubstantiated contradictory claims, all the more so if it were literally a matter of life and death.

However, anyone who has ever engaged in a political debate knows that changing deeply held beliefs is no simple matter.

In Semmelweis’s case, his colleagues clung to various baseless explanations for childbed fever which, nevertheless, aligned with accepted wisdom of the time, including attributing the illness to exposure to a noxious atmosphere of some sort. So, when substantial evidence convinces us that a prevalent belief has harmful consequences and that implementing a change in the behaviors related to that disputed notion could bring about significant benefits, how do we persuade others to accept a new concept?

To a large extent, Semmelweis had himself to blame for his failure to gain acceptance of his new theory of childbed fever’s origins. His case is fascinating as, in many ways, he behaved in a manner that should, indeed, have caused his peers to suspect he was peddling pseudoscience. He obstinately refused to do basic research studies to prove his speculative conclusions were correct despite the urgings of his closest colleagues to do so. He was equally stubborn in refusing to write up his clinical findings for publication in a reputable medical journal. He believed that the logic of his reasoning should suffice, especially given that the disinfection protocol implemented on the basis of his conclusions had led to such a dramatic reduction in mortality. For a few colleagues, that did, in fact, suffice, but if he had only had enough humility to recognize the need for a few rather simple additional steps, his paradigm-shifting approach likely would have achieved broad and ongoing acceptance.

His medical peers’ wariness of accepting results that had not been supported by straightforward experiments and had not been published was understandable. In contrast to a promoter of pseudoscience, a curious scientist would jump on the opportunity to easily prove a hypothesis. A hallmark of pseudoscience is the reliance on dubious sources. Semmelweis himself was in a position to create that reliable source, but, instead, he mainly offered a strong opinion based on his experience.

He resorted to personal attacks to shut down his critics. Semmelweis blatantly accused his colleagues of killing their patients by refusing to accept his theory. Although the physicians were, in fact, inadvertently causing the deaths of their patients, this approach only elicited defensiveness rather than persuading them to change their opinions and practices. Semmelweis was brash, young, and perceived as an outsider by his peers, which all diminished his power to persuade others to accept personal culpability along with a completely new theory of disease transmission, a theory that challenged their professional self-image as healers.

If physicians at the time had employed Carl Sagan’s Baloney Detection Kit, it would have rung many alarm bells. For example, he did not seek independent confirmation of the facts as recommended by Sagan. He certainly did not encourage substantive debate and, in fact, reacted aggressively to any perceived critiques. Rather than presenting research evidence, he primarily argued from authority. Sagan cautioned against becoming overly attached to a single hypothesis. Semmelweis “had reached a point where his sense of self had become so interwoven with his theory that its acceptance or rejection was equivalent to his own.” As noted, he engaged in ad hominem attacks, which Sagan cautioned was a marker of purveyors of baloney.

Reliable evidence is necessary though not sufficient to persuade others. When a new belief is perceived as a threat to one’s core identity, for example, when a physician would need to accept that he is causing death rather than healing, resistance to such a belief is likely to be fierce. Overcoming that resistance requires a profound level of trust. Thus, people are most likely to accept radically different views of their world when their close friends, family, or their accepted authorities are the messengers. Empathy, rather than humiliation, is called for.

Presenting facts may suffice to persuade a rational person about a topic about which they hold no strong opinions. However, convincing a strong believer to abandon a belief that relates to their very identity requires sustained efforts to build trust, often with one individual at a time, by understanding and validating that person’s values and concerns, including any perceived threats and fears. Such an edifice of trust can only be built painstakingly, one brick at a time. With the right approach, when the person proposing a radical shift in perspective is no longer seen as “them” but as “one of us,” persuasion is possible (albeit not guaranteed by any means) even when the new belief is perceived as challenging an accepted worldview.

We know this is possible, as Joseph Lister’s patience, humility, and gentle approach, accompanied by determination to conduct the required experiments and publish his results, eventually succeeded in changing minds and practices and saving lives by preventing puerperal fever.

Steve Sobel is a psychiatrist.