THE RULE OF THREE
The "Rule of Three" provides guidance for simplifying presentations by using three or fewer main ideas.
DEFINITION of the " Rule of Three:" use 3 or fewer important elements at each level of an argument. Repeat important conclusions 3 or more times.
WHY limit and repeat information within a presentation?
The "Rule of Three" is based on the hypothesis that people have a preference for things that are presented in groups of three. Unfortunately, there does not appear to be direct evidence for the "Rule of Three" hypothesis. However, much anecdotal evidence supports the idea that people like tripartite (three-part) structures. For example, the "Five Paragraph Essay" is commonly taught at many educational levels. Five paragraph essays are based on 3 body paragraphs that defend 3 main ideas. Research grant applications are frequently structured around 3 "Specific Aims," or objectives of a project. The U.S. (and other) governments have three main branches, etc. Therefore, important examples of 3-part structures abound.
Of course, there are also many examples of structures with more (or fewer) than three parts (e.g. 4-part IMRaD scientific papers, 5 act plays, etc.). Therefore, despite its name, the "Rule of Three" is not really a "Rule" at all, but more what you'd call "guidelines" than actual rules (Sparrow, 2003). Nevertheless, the Rule of Three remains a useful principle to help reduce and reinforce information presented to audiences.
The "Rule of Three" for scientific communication actually consists of two related guidelines: (1) Use 3 or fewer important elements (e.g. main conclusions of a paper) in each level of an argument; and (2) Repeat elements that are important for audiences to understand and remember 3 or more times.