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The elaboration likelihood model (ELM) of persuasion (Petty & Cacioppo, 1986) is a model of how attitudes are formed and changed (see also attitude change). Central to this model is the elaboration continuum, which ranges from low elaboration (low thought) to high elaboration (high thought).

The ELM distinguishes between two routes to persuasion: the central route and the peripheral route. Central route processes are those that require a great deal of thought, and therefore are likely to predominate under conditions that promote high elaboration. Central route processes involve careful scrutiny of a persuasive communication (e.g., a speech, an advertisement, etc.) to determine the merits of the arguments. Under these conditions, a person’s unique cognitive responses to the message determine the persuasive outcome (i.e., the direction and magnitude of attitude change). So, if favorable thoughts are a result of the elaboration process, the message will most likely be accepted, and if unfavorable thoughts are generated while considering the merits of presented arguments, the message will most likely be rejected.

Peripheral route processes, on the other hand, do not involve elaboration of the message through extensive cognitive processing of the merits of the actual argument presented. These processes often rely on environmental characteristics of the message, like the perceived credibility of the source, quality of the way in which it is presented, the attractiveness of the source, or the catchy slogan that contains the message (Miller, 2005, p.129).

The two factors that most influence which route an individual will take in a persuasive situation are motivation (strong desire to process the message) and ability (actually being capable of critical evaluation). Which route is taken is determined by the extent of elaboration. Both motivational and ability factors determine elaboration. Motivational factors include (among others) the personal relevance of the message topic, accountability, and a person’s "need for cognition" (their innate desire to enjoy thinking). Ability factors include the availability of cognitive resources (e.g., the presence or absence of time pressures or distractions) or relevant knowledge needed to carefully scrutinize the arguments. Under conditions of moderate elaboration, a mixture of central and peripheral route processes will guide information processing.

In Communication and persuasion: Central and peripheral routes to attitude change, Richard Petty and John Cacioppo provide a helpful visual representation of the processes involved in the ELM

In addition to these factors, the ELM also makes several unique proposals.

• Attitudes formed under high elaboration are stronger (more predictive of behavior and information processing, more stable over time, more resistant to persuasion) than those formed under low elaboration.
• Variables can serve multiple roles in a persuasive setting depending on other contextual factors (examples below).
  • In an advertisement for a new store, the actor's bright white smile might serve as a peripheral cue that makes the source of the message appear more attractive. But, in a commercial for toothpaste, the same bright white smile would be a central cue in the message of how well the toothpaste works.
  • Under high elaboration, a given variable (e.g., source expertise) can either serve as an argument (“If Einstein agrees with the theory of relativity, then this is a strong reason for me to as well”) or as a biasing factor (“if an expert agrees with this position it is probably good, so let me see what else agrees with this conclusion” (at the expense of information that disagrees with it)).
  • Under conditions of low elaboration, a given variable can act as a cue (e.g., through the use of an “experts are always right” heuristic – note that while this is similar to the case presented above, this is a simple shortcut, and does not require the careful thought as in the Einstein example above).
  • Under conditions of moderate elaboration, a given variable can serve to direct the extent of information processing (“Well, if an expert agrees with this position, I should really listen to what (s)he has to say”). Interestingly, when a variable affects elaboration, this can increase or decrease persuasion, depending on the strength of the arguments presented. If the arguments are strong, enhancing elaboration will enhance persuasion. If the arguments are weak, however, more thought will undermine persuasion.

More recent adaptations of the ELM (e.g., Petty, Briñol, & Tormala, 2002) have added an additional role that variables can serve. They can affect the extent to which a person has confidence in, and thus trusts, their own thoughts in response to a message. Keeping with our source expertise example, a person may feel that “if an expert presented this information, it is probably correct, and thus I can trust that my reactions to it are informative with respect to my attitude”. Note that this role, because of its metacognitive nature, only occurs under conditions that promote high elaboration.

• Eagly, A. H., & Chaiken, S. (1993). Psychology of attitudes. Fort Worth, TX: Harcourt, Brace, Jovanovich.
• Miller, K. (2005). Communication theories: Perspectives, processes, and contexts. New York: McGraw-Hill.
• Petty, R. E., Briñol, P., & Tormala, Z. L. (2002). Thought confidence as a determinant of persuasion: The self-validation hypothesis. Journal of Personality & Social Psychology, 82, 722-741.
• Petty, R. E., & Cacioppo, J. T. (1986). Communication and persuasion: Central and peripheral routes to attitude change. New York: Springer-Verlag.
• Petty, R. E., & Wegener, D. T. (1999). The Elaboration likelihood model: Current status and controversies. In S. Chaiken & Y. Trope (Eds.), Dual Process Theories in Social Psychology (pp. 41-72). New York: Guilford Press.