Persuasion: does adding more arguments help?
When advocating a process change, a manager may be tempted to keep adding reasons until the case appears beyond dispute. The more precise managerial question is whether adding secondary arguments strengthens a recommendation for people directly affected by its consequences.
What the literature establishes
Richard E. Petty, John T. Cacioppo and Rachel Goldman (1981, Journal of Personality and Social Psychology) studied persuasion by varying factors including an issue's personal relevance, argument quality and the expertise attributed to the source. When the issue was more personally relevant, participants' attitudes depended more on argument quality; when it was less relevant, source expertise carried more weight. Different recipients therefore do not necessarily assess the same message against the same criteria.
Quantity can act as a cue rather than evidence
Richard E. Petty and John T. Cacioppo (1984, Journal of Personality and Social Psychology) experimentally distinguished the effects of argument quantity and quality. Under low involvement, a larger number of arguments could encourage persuasion without close scrutiny of their strength; under high involvement, the effect of quantity depended on quality. Accumulating reasons can therefore create an impression of extensive support without providing a more robust case.
The premature conclusion
One might conclude that documents should always be shortened to retain only a few arguments. Yet these studies establish neither an optimal length nor an ideal number: above all, they show that the effect of quantity depends on how the message is processed. For a technical decision, removing information needed to assess risks would be a misguided application of these findings. (our executive and employee training programmes)
What the evidence does not directly establish for practice
These experiments concern attitudes towards proposals presented in an experimental setting, not the validation of industrial processes. Personal relevance as manipulated in a study does not precisely capture professional responsibility, technical expertise or the time available to examine a case. Finally, a more persuasive recommendation is not necessarily more sound: agreement and decision quality need to be assessed separately.
A practical check in Neuchâtel
As part of SHR's “Communication” programme, a Neuchâtel company working in microtechnology, watchmaking or precision microelectronics could test two versions of a recommendation using an anonymised technical case, with no operational decision at stake. Both versions would retain the same critical data, risks and uncertainties, but one would add explicitly identified secondary arguments. Randomly assigning participants to the versions and then individually recording their support for the recommendation and their ability to identify the main risk against a predefined rubric would help distinguish persuasion from understanding. This local check would not establish a universal rule, but it would indicate whether a longer document delivers anything beyond greater agreement. To go further: explore the Communication training in Neuchâtel in the canton of Neuchâtel, or browse our executive and employee training programmes in Switzerland.
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