01 / UNDERSTAND
What are design principles?
Design principles are shared statements that guide decisions about a product or service. They express what the team should preserve or prioritise across many specific choices. A useful principle connects a reason to an observable implication for the work.
This method concerns principles for a particular product or service, rather than visual composition rules such as balance and contrast. A principle should help choose between plausible options. If every proposal can claim to follow it, its wording or scope needs work.
Why use Design Principles?
Teams often repeat the same discussion in different forms: speed versus reassurance, consistency versus context, or automation versus human help. Principles make the reasoning behind these choices available beyond the original conversation.
They do not remove judgement. Their value is in making decisions more explicit and reviewable, especially when several people or teams contribute to the experience.
When to use it
USE IT WHEN
Recurring design decisions need a shared basis beyond personal preference.
Research reveals needs that should shape more than one feature.
Several teams need coherence while retaining room for context.
When to choose another method
Use User Interviews and Affinity Mapping first if the principles would otherwise be based only on opinion.
Use a specific acceptance criterion when the requirement is narrow and directly testable.
Use Usability Testing to examine whether a design works; agreement with a principle is not evidence of successful use.
What you’ll need
Bring research themes, organisational commitments and examples of decisions the team struggles to make. Distinguish obligations that must be met from preferences that guide choices. Include the people who will apply the principles in design and delivery.
Keep the initial set small enough to discuss through real examples. Record evidence gaps instead of presenting a new principle as an established user need.
What a useful design principle contains
Keep the elements that help answer your question and support a decision.
A short direction that people can remember and apply.
The need or commitment that makes the direction important.
Research references or an explicit assumption supporting the rationale.
What the team should do differently in a real decision.
What the principle does not mean and where tension may arise.
An example that can expose vague wording or conflicting interpretations.
02 / PUT IT INTO PRACTICE
How to define design principles
Keep evidence and assumptions distinct. Revisit your work when new information changes your understanding.
01
Collect recurring decisions
Identify choices where the team repeatedly disagrees or produces inconsistent outcomes.
A repair booking service alternates between optimistic estimates and cautious status messages.
02
Connect decisions to needs
Review the evidence and commitments behind each tension. Separate observation from aspiration.
The illustrative brief concerns customers needing to plan around uncertain completion times.
03
Draft a direction and rationale
Write a concise statement, explain why it matters and avoid abstract adjectives alone.
Make uncertainty visible before people commit. Explain how that supports planning.
04
Add implications and boundaries
Describe a decision the principle would change and a possible misinterpretation.
Show an estimate and what could change it; do not replace useful information with vague disclaimers.
05
Test against competing options
Apply the draft to realistic alternatives. Ask different team members to explain their choices.
Compare a precise but unsupported completion date with a range and a clear next update.
06
Adopt, use and review
Agree ownership, where the principles are used and what would trigger revision.
Use the principle in booking and status reviews, then revisit it when evidence changes.
Example: communicating repair completion times
This is a fictional design example, not a claim about research findings. A repair service needs to communicate when an item might be ready. The team compares a confident single date, a broad range with no explanation and an estimate that states what could change it.
The proposed principle is ‘Make uncertainty visible before people commit’. Its rationale is that people need enough information to plan. Its implication is to distinguish an estimate from a confirmed date and explain when the next update will arrive.
The principle does not mean adding cautionary text everywhere. A message saying ‘times may vary’ would satisfy its wording superficially while offering little help. The team therefore adds a review question: can someone tell what is known, what is uncertain and what happens next?
The chosen message remains a proposal to test. The principle improves the decision’s rationale; it does not establish that the message is understood.
03 / BELOW THE SURFACE
Below the surface: test a principle with a difficult choice
Principles often sound useful because the examples used to explain them are easy. A stronger test is a case in which two reasonable principles favour different choices.
DISCRIMINATION
Which plausible option would this rule out?
A principle should affect a choice, not merely describe an ambition.
TENSION
What does a competing principle protect?
Name the consequence of applying either direction too rigidly.
REVISION
What evidence would change the principle?
Keep the rationale and review trigger attached to the statement.
In the repair example, ‘Keep messages concise’ may conflict with ‘Make uncertainty visible’. Hiding uncertainty creates a shorter message, while listing every dependency overwhelms the reader. Neither slogan resolves the design.
Ask what each principle protects and what harm its extreme interpretation could cause. The team might keep the initial message short while making the estimate, next update and route to more detail explicit. Record why that arrangement fits this decision rather than turning it into a universal rule.
A useful principle can rule something out. Ask which plausible proposal the team would reject because of it. If the answer is none, make the implication more specific. The difficult choice exercise is editorial guidance for reviewing principles, not a scoring system or proof of design quality.
Design Principles working canvas
Use page one to develop one principle from a recurring decision and its evidence. Duplicate it for other principles. Use page two to examine a difficult choice, a competing principle and a review trigger. The PDF is a working record rather than a poster of finished statements.
Practical tips
Pair each short statement with an example and a boundary.
Ask another team member to apply the principle without coaching.
Bring principles into actual reviews instead of leaving them in a presentation.
Common mistakes
Using agreeable adjectives that cannot distinguish between options.
Copying another organisation’s principles without examining the context.
Confusing a preferred solution with a lasting direction.
Treating principles as exemptions from evidence or mandatory requirements.
What you’ll get
A concise set of directions with reasons, implications and review cases. Use them to explain decisions, record exceptions and guide the next prototype; return to the evidence when their application remains uncertain.