Understanding how principles help with decision making starts with understanding how they differ from rules. The distinction matters. Rules and principles serve very different purposes. Yet many “design principles” are written more like rules.

What rules do

Rules remove ambiguity. Rules are rigid. They tell people exactly what must happen. Rules usually lead to a consequence, either:

  1. the rule is broken, or
  2. something happens when the rule isn’t followed.

For example:

Our logo must always appear on a white background.

This rule guarantees consistency. Everyone knows exactly what to do.

A rule like this prevents designers from using the logo on:

  • coloured backgrounds
  • photography
  • illustrations
  • gradients

Even if those options might work perfectly well.

Rules assume there is one correct answer or only one solution has been considered.

In many situations, especially technical or legal ones where a level of compliance has to be reached, rules are appropriate.

What principles do

Principles work differently.

Instead of prescribing a single outcome, they describe what a good outcome should achieve.

Consider the same example written as a principle:

The logo should be clearly legible.

The goal is the same: protecting the visibility of the logo. But now designers have room to explore solutions.

They can place the logo on different backgrounds, colours or images, as long as the logo remains easy to see.

The principle does not dictate the design.

It guides judgement.

Why this matters

Design decisions are rarely as simple as deciding how to display a logo. Design rarely involves a single correct answer. Most design work involves balancing competing priorities between different people and different goals, navigating budgets, timelines, and politics.

For example:

  • clarity vs completeness
  • consistency vs flexibility
  • simplicity vs capability

Rules struggle in these situations because they assume the answer is fixed.

Principles acknowledge that design decisions often involve tension between competing forces.

They help teams navigate those trade-offs.

Visualising how principles work

One way to think about this is to imagine a design decision being shaped by different priorities pulling in different directions. Principles help teams balance those forces and arrive at a thoughtful outcome.

This idea is illustrated in the sample chapter of Design Principles in Practice, where the relationship between design decisions and principles is explored in more detail.

→ View the sample chapter

Rules and principles both have their place

Most organisations need both. Rules are useful when consistency or compliance is essential. Principles are useful when teams need guidance to make thoughtful decisions.

Rules define the answer.

Principles help teams find the best answer.

Or more simply:

Rules remove choice. Principles guide choice.

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