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[…] consistency in computer systems constitutes a promise to the user. And it is not polite to break a promise.
— Jacob Nielsen, Coordinating User Interfaces for Consistency, 1989

Are you a designer? If you are, you might identify with a feeling many designers have: it's hard to think of a less exciting topic than consistency.

When I talk to designer friends and colleagues, I usually hear: “yes, consistency is very important, but…”, followed by a rambling speech on design freedom, creativity, the risks of uniformity and boredom, and the missing WOW factor.

However, I hardly ever hear this from the people using the software.

Design-minded non-designers are often worse, as they lack the professional understanding of the importance of consistency. When designers break consistency rules, they at least have a bad conscience. We all know how important consistency is, but it requires discipline. Consistency is often perceived yet another restriction in a profession that is already subject to so many rules and limitations defined by others (such as technology, style guides, legislation, and users!).

I have the feeling that this resentment towards consistency also stems from a lack of understanding of what consistency really is. And I would claim that, if done in the right way, consistency doesn’t have to limit your creativity, but helps your mind to focus on solving the right problems.

In this series of articles, I want to give you my perspective of this topic. Starting with a brief introduction, followed by some more theory, an overview of the dimensions that can help establish design consistency and finally some thoughts about processes and organizational setup to establish a culture of design consistency.

What is Consistency?

Consistency describes the quality of the relationship between your user’s expectations – his or her mental model – and your product. It determines how well your product meets these expectations in a number of dimensions. In other words: there is no absolute consistency, and consistency is not limited to a single aspect of the experience.

User expectations don't just depend on the business domain (such as accounting or manufacturing). They are also shaped by the platform the user works with (such as Windows or Mac), and the features of similar products from the same vendor. If you want to be consistent, you need to take all these expectations into account.

Does that sound boring? In fact, designing for consistency means nothing more than respecting users and their expectations. That sounds like good design to me.

However, this definition also reveals one of the biggest challenges. Not only are all users and their expectations different, but we also need to strike a balance between expectations at domain, product, and platform levels.

  • Products that are only consistent with the domain standards might be best-in-breed but will not provide synergies and integration effects with other solutions.

  • Products that are only consistent within a product portfolio create high synergies but might be of little use if they are too far away from how things run in the business domains.

  • Platform consistency helps users to switch applications across vendors. Sometimes this type of consistency is intentionally violated to create lock-in effects.

A piece of software can be highly consistent with the platform, but it might still not reflect the way things are done in the given domain or fit in with your other products – domain experts will hate it and there won't be any synergies with your other solutions.

Even if your software is highly consistent with your other products and conforms to the platform standards, it will still be a failure if it doesn't follow the domain standards. This is why we do usability tests and user research to learn more about the domain conventions.

Ideally, you will create products that are consistent at all these levels. This will also help users to move in your direction.

Why Is Consistency Important?

Consistency is one of the most powerful usability principles: when things always behave the same, users don’t have to worry about what will happen.
--   Jacob Nielsen

Consistency makes sure that things work as expected. The more consistent a solution is, the less attention is directed to the user interface and the more users can focus on their actual work. Cognitive load and errors are reduced, and users can work faster.

Consistency helps people to best leverage the investments they have made learning and applying your tools. It is easy to understand the relevance of this, bearing in mind that time and expertise are THE values employees bring to work.

Consistency affects all aspects of design in everyday life and we only notice when it’s not there.

Is inconsistency always bad? Not really. Sometimes it is the result of historical processes outside of our control, and sometimes inconsistencies are used intentionally to achieve certain effects.

This example shows how international standards enable consistency in the design of ATM numeric pads so that you can withdraw cash wherever you are. The same number layout, the same positioning for the functions, and the same color codes. You don't have to be able to read the labels to know what to do.

At the same time, the numeric pad on the computer keyboard is the other way around. Historically, this layout was designed for data typists and has never been changed to avoid reducing their entry speed. By contrast, today's new designs for phones and other numeric pads follow the layout with 1, 2, 3 at the top. Is this an issue? I’d say not so much, as these two layouts are hardly ever used for the same tasks, and users can adjust their expectations accordingly.

However, it can get tricky if there are two different designs for the exactly the same task. This is something we typically see with the gear boxes in different car brands. Have you ever switched between a Mercedes and a BMW and tried to find the reverse gear?

Inconsistencies can also be used to differentiate brands and shape the habits and preferences of customers. Once you are used to a certain way of doing things you might just want to stick to it and go for brands that are consistent with your habits.

Another case for making intentional use of inconsistencies is when critical tasks have to be carried out very consciously and carefully. A high level of consistency reduces the cognitive load but can also reduce attention. People rely on automated learned processes and might click before they think because they believe they know what will happen. One way to avoid automation errors like this can be to arrange actions inconsistently to force the user's attention. Here, inconsistency is used consciously to design for error prevention and heighten attention.


Consistency is much better than its reputation. If done right, it means that you design in accordance with your user’s expectations, reducing the mental load, the risk of errors, and completion times. In other words, consistency is one of the most important aspects of usability.

Further, consistency doesn’t mean uniformity. Since consistency isn't an absolute value but the relationship between the design and different dimensions of the user’s expectations, there are many ways to implement it. Consistency can help you focus your creativity on the questions relevant to the user.

Lastly, consistency can be violated on purpose. Automation errors can be prevented by forcing users to actively analyze the screen. And brands can use inconsistencies with standards or their competition to shape a distinct brand experience and increase customer affinity by habituation. In homeopathic doses, inconsistency can be a great design tool.

Are you curious to learn more? In the upcoming parts of this series I will talk about different aspects of consistency in our user interfaces, and how we established a process for defining company-wide UX consistency standards.

In Part 2 you can learn more about the theory behind consistency and how it impacts our ability to learn and interact with applications.