'You cannot reason people out of an opinion they have not reasoned themselves into.'
That's a modern way of saying what Jonathon Swift observed in 1721.
Wouldn't persuasion be so much easier if we humans were entirely logical? The research makes it clear that we're not. We just think we are.
We treat our own opinions as more logical and well-informed than other people's opinions. We may not go as far as talking about alternative facts and rejecting other people's information or opinions as fake news, but it's only human to struggle with objectivity.
How much of a struggle?
Psychologists have studied more than 90 ways we humans compromise our objectivity. Let's just look at a selection.
Confirmation bias We search for, remember and interpret information that matches our opinions
Availabilty bias We develop opinions based on immediate examples. Instead of researching a topic we reason, 'If I can remember it, it must be important'. Example: We remember the wreckage of car crashes on TV and assume that the risk of driving is far greater than the risk of dying from disease. (The leading cause of death around the world is heart disease. Death from all accidents only makes it to fourth place.)
The bias blind spot We're quick to recognise bias in others and believe we are more objective than they are.
The rhyme is reason bias If it rhymes, it's more persuasive. A classic example:'If the gloves don't fit, you must acquit' - from the trial of OJ Simpson
The gambler's fallacy Believing that past chance events influence future chance events. Example: the gambler who believes that the pokie machine he's on is due to pay out very soon because he's won nothing so far.
The zero risk bias It's when we prefer to eliminate a small risk over a greater risk. Example: not vaccinating our kids because there's a tiny risk of an adverse reaction, while risking them catching deadly or debilitating diseases.
So how do we persuade anyone?
Find common ground as a starting point. Example? 'We both want to protect our children from disease.' Then move gradually to your argument in favour of immunisation.
Ask questions. 'Can you tell me how you know that?' 'Have you considered...' (followed by contrary evidence)
It's still going to be a challenge and the more emotional the issue, the greater the challenge.
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