How to write a persuasive message

Both are false (Hitler was born in 1889), but experiments have shown that the first is more likely to be believed. More advice: if your message is to be printed, use high- quality paper to maximize the contrast between characters and their background. If you use colour, you are more likely to be believed if your text is printed in bright blue or red than in middling shades of green, yellow or pale blue.

If you care about being thought credible and intelligent, do not use complex language where simpler language will do. My Princeton colleague Danny Oppenheimer refuted a myth prevalent among undergraduates about the vocabulary that professors find most impressive. In an article titled “Consequences of Erudite Vernacular Utilized Irrespective of Necessity: Problems with Using Long Words Needlessly,” he showed that couching familiar ideas in pretentious language is taken as a sign of poor intelligence and low credibility.

In addition to making your message simple, try to make it memorable. Put your ideas in verse if you can; they will be more likely to be taken as truth. Participants in a much cited experiment read dozens of unfamiliar aphorisms, such as:

Woes unite foes.
Little strokes will tumble great oaks.
A fault confessed is half redressed.

Other students read some of the same proverbs transformed into non-rhyming versions:

Woes unite enemies.
Little strokes will tumble great trees.
A fault admitted is half redressed.

The aphorisms were judged more insightful when they rhymed than when they did not.

Finally, if you quote a source, choose one with a name that is easy to pronounce. Participants in an experiment were asked to evaluate the prospects of fictitious Turkish companies on the basis of reports from two brokerage firms. For each stock, one of the reports came from an easily pronounced name (e.g., Artan) and the other report came from a firm with an unfortunate name (e.g., Taahhut). The reports sometimes disagreed.

The best procedure for the observers would have been to average the two reports, but this is not what they did. They gave much more weight to the report from Artan than to the report from Taahhut. Remember that System 2 is lazy and that mental effort is aversive. If possible, the recipients of your message want to stay away from anything that reminds them of effort, including a source with a complicated name.

All this is very good advice, but we should not get carried away. High quality paper, bright colours, and rhyming or simple language will not be much help if your message is obviously nonsensical, or if it contradicts facts that your audience knows to be true. The psychologists who do these experiments do not believe that people are stupid or infinitely gullible. What psychologists do believe is that all of us live much of our life guided by the impressions of System 1— and we often do not know the source of these impressions.

How do you know that a statement is true? If it is strongly linked by logic or association to other beliefs or preferences you hold, or comes from a source you trust and like, you will feel a sense of cognitive ease. The trouble is that there may be other causes for your feeling of ease— including the quality of the font and the appealing rhythm of the prose— and you have no simple way of tracing your feelings to their source.

Excerpted from Thinking, Fast and Slow by Daniel Kahneman Copyright © 2011 by Daniel Kahneman. Excerpted by permission of Doubleday Canada, a division of Random House of Canada Limited. All rights reserved. No part of this excerpt may be reproduced or reprinted without permission in writing from the publisher.

Daniel Kahneman is Eugene Higgins Professor of Psychology Emeritus at Princeton University and a professor of public affairs at the Woodrow Wilson School of Public and International Affairs. He is the only non-economist to have won the Nobel Prize in Economic Sciences; it was awarded to him in 2002 for his pioneering work with Amos Tversky on decision-making.