In the late 1970s, Richard Petty and John Cacioppo studied how motivation affects persuasion. Their work resulted in their “elaboration likelihood model” (ELM).¹ We use the ELM in all sorts of decision making, from choosing a spouse to tapping a buy button.

Petty and Cacioppo proposed two primary routes to persuasion: a central and a peripheral route. When we are motivated to understand a subject, we are more likely to think about it and to elaborate on it. Petty and Cacioppo called this the central route. For example, say you are serving as a member of a jury, deciding the fate of a corrupt politician. Opposing lawyers offer their evidence. The FBI recorded the defendant demanding free spray tans from a New York salon. Empty bronzer bottles contain the defendant’s fingerprints. Witnesses testify that they watched the defendant leave without paying. The defense attorney says his client was merely misunderstood. You weigh the testimony. You reread the transcripts, debate the merits, and deliver your verdict. Such careful consideration is the central route to persuasion.

People also have a peripheral route to follow. If the central route fails to persuade, people will consider surface characteristics. Perhaps you base your verdict on the attorney’s expensive-looking suit, the judge’s New Jersey accent, or the defendant’s ridiculous comb over. These are cues. If a cue is present, a person may still be persuaded. The peripheral route is usually not as effective as the central route, but, over time, it still may persuade.

Digital experiences leverage the central and peripheral routes. A website’s detailed product information can provide a compelling case for making a purchase. Each fact serves as evidence—size, shape, weight, color, form, and function. A customer ruminates on this information, enhancing the product’s persuasive effects along the central route. Attractive visual design, typography, and photography all contribute to an application’s ability to persuade users, operating along the peripheral route (see Figure 23-1).

Persuasion surrounds us. Thousands of messages compete for our attention, everything from billboard advertising to mobile app notifications. Each attempts to inform us of something new. However, depending on the route the message takes, its persuasive effects may quietly take hold over time or strike like a judge’s gavel.