The One-Idea-Per-Slide Principle
The most transformative principle in presentation design is deceptively simple: every slide should contain one idea. Not one topic, not one section, not one category — one specific, clearly articulable idea that the audience should take away from that slide. If a slide contains two ideas, it creates a divided attention problem: the audience must process both ideas simultaneously while also listening to the speaker, and one or both ideas will be partially processed. When each slide contains exactly one idea, the audience can absorb that idea fully while listening to the speaker elaborate on it.
The one-idea principle has a testable implication: you should be able to state the single idea of each slide as a declarative sentence in 8 words or fewer. 'Sales increased 34% after the new pricing model' is one idea. 'Background, current state, and implications of our pricing strategy' is three ideas. When you cannot state the slide's idea in a single concise sentence, the slide contains more than one idea and should be split.
The most common violation of this principle is the traditional corporate presentation style: text-heavy slides with five to seven bullet points, each containing a fragment of a different idea. This style developed in the era when slides were presenter notes projected for the audience's benefit — but it produces a catastrophic reading conflict. When text is visible on screen, the audience reads it. When the speaker is speaking, the audience hears them. These two activities use the same language processing systems in the brain and cannot occur simultaneously. The result: when text-heavy slides are used, audiences are always partially behind on either the slide content or the speaker's words. The cure is removing text from slides entirely and putting information either in the spoken presentation or in a written document — not in both places simultaneously.
This is the insight behind Amazon's famous 'no PowerPoint in meetings' policy, replaced by pre-distributed memos. The memo serves the function of communicating complex information in depth; the meeting serves the function of discussion and decision. These are two fundamentally different information activities requiring different formats — merging them into a narrated slideshow serves neither purpose well.