Why should deductive storylines always have three top-level supports?

Only three ideas will provide the right combination of logical strength and clarity

Having more than three is

  1. Logically risky. The more links you have that must be logically tight for the conclusion to be true, the more risk there is that your story will be logically flawed
  2. Hard on your audience. The more steps you take someone through, the more they have to follow and the harder it is for them to understand your ideas.

Having less than three does not allow you to use deductive logic properly to tell your story.

A deductive storyline is based on a chain of deductive reasoning where two ideas – a statement and a comment on that statement – combine to lead you to the third, which is a conclusion. If you only had two supports, they would necessarily be a statement and a conclusion (which we call a recommendation). This leaves out the comment, or ‘however', which is a pivotal part of the deductive chain.