What consistency means for a cat and what it means for your interface

In interface design, the term consistency is part of the professional jargon. It is used for everyday feedback and in long term concepts. It is also common ground with developers and clients. Consistency is an important evaluation criterium. Enough reasons to get a good handle on the term.


Andreas and Jonas decided to bounce ideas on consistency back and forth – something like a good lunch conversation. As interaction designer and visual designer, we have similar, but distinct points of view, so we approached consistency from a number of different angles.

Cat Content

Jonas Stallmeister: Cat content might be a good way to get the conversation started. Three months ago, I became the owner of two young cats, which are currently settling into our household. I noticed what experts like the ASPCA agree on: “[House] Cats tend to prefer consistency over change”.

Put into interface design terms: they demand a consistent user experience from the household. One hundred grams of food at seven AM and six PM. Less, and they’ll be annoyed. Access to every room, or they’ll let you know. They learn through consistency: stay off the kitchen counter or get sprayed with water. And they know that there are two kinds of inconsistency: annoying, like oversleeping humans missing the expected breakfast time, and delightful, like a surprise snack. Those basics seem to apply to human user experience as well, right?

Andreas Burghart: There is research on so called random reinforcement from the psychologist B.F. Skinner, who made following experiment: rats can press a lever, and every hundredth time they get food. This is a very consistent behavior of the lever. If the food release is random – so to say inconsistent – rats press the lever more often.[1]

I can imagine that it might be similar compared to human experience. Perhaps the randomness or inconsistency leads to a good user experience, because it causes an exciting unpredictability. But as exciting unpredictability might be, we also have to take into account, that predictability leads to advantages when it comes to interface design. As you say, consistency is helpful for the learning process for the cats. So the consistency helps them to understand when and where they get their food. This is also important for interfaces. Because consistency helps to predict where users can find which function and it also helps them to predict the behavior of the interface, which increases usability.

But I ask myself whether an interface is too boring, if it is completely predictable? Can we make interfaces less predictable while maintaining learnability and usability? For example, if we imagine an interface in which users should learn how to save and also be motivated to save often: than I can imagine that the consistent use of the floppy disk in many software products helps the user to learn how to save. But when it comes to motivating the user to save often or to reinforce his/her saving behavior, we could use inconsistency. For example there could be a random feedback after the save button is pressed. Sometimes a green checkmark could be displayed. And sometimes you could see an animation, in which a box is closed.

Consistent user experience with an element of surprise.

Consistent user experience with an element of surprise. Photo credit: Comrade Foot. CC BY-SA 2.0

Jonas: The excitement of unexpected rewards worked in Skinner’s box, and it is working in a lot of casual games to the point of addiction. In productive interfaces, graphics are a good way to deliver unexpected rewards while keeping consistent, learnable interactions. One good example could be Google’s doodles. They do not change the look and behavior of the central functionality, they “Don’t make me think“, as Steve Krug summed it up. They just surprise me and invite me to think – a little, if i’m free, with a visual snack on the side. They associate playfulness and curiosity with Google’s brand – quite literally.

Lets take surprises a little further:

– “Good evening! My name is Tobias, and I’m here to make love to your daughter.”
– “To what!?!”
– “To-bias!”

Humor is often based on surprises – and the more delightful the surprise, the better the joke. Jokes work because we expect a certain consistency in conversations – no abrupt changes in topic, tone or the way a term is used. This expectation of consistency sets us up to be surprised by a joke in conversation. We also expect interfaces to be consistent, which gives us the opportunity to design humorous surprises. A well-placed easter egg, charming confirmation text, careful animation or character can earn the interface a smile and good will – if they don’t interfere with the workflow too drastically.

Andreas: So I think we agree, that inconsistencies on the one hand can bring pleasant surprises. On the other hand, we are even able to influence the user behavior with it. A further function is that you can draw attention to something: an inconsistency within the design is similar to breaking a grid or breaking a rule.

When we talk about inconsistency we cannot leave out Robert B. Cialdini. He describes the following experiment by Freedman and Fraser: people were asked to accept and put up a little three-inch-square sign that read BE A SAFE DRIVER. They should put it up wherever they wanted to, as long as it is visible.[2] They made a small commitment. A few weeks later the same people were asked by another person to install a huge public-service billboard on their front lawns. 76 percent of them agreed on it, because they wanted to maintain a consistent self-image, otherwise they are affected by a so called cognitive dissonance. But it is not only the self-image in which humans seek consistency. We also want others to think that we are consistent: “Inconsistency is commonly thought to be an undesirable personality trait. The person whose beliefs, words, and deeds don’t match may be seen as indecisive, confused, two-faced, or even mentally ill.”[3] When we keep in mind Alan Coopers design principle “software should behave like a helpful human”[4], we can say that the interface should have a nice personality. And one aspect of a nice personality is not behaving inconsistent.

We use five senses to look for coherence and build trust

In the real world, we can use five senses to look for coherence and build trust. Photo credit: Bridget Coila. CC BY-SA 2.0

Jonas: Yes! We expect consistency, from ourselves, from others, from interfaces, from the world surrounding us. It makes life easier. Otherwise we’d have to constantly worry about what to expect from conversations, about how to control a computer, about how to get home.

This is the point where I see a connection between consistency and trust. We never can be completely sure. Our senses may be fooled by illusions, people may lie to us, gut feelings may be wrong. Whatever way we judge something to be true, it becomes more reliable if it is coherent with other things we take as true. We try to have a coherent world view without cognitive dissonance. Once we’ve fit consistent persons, behaviors, interfaces into our world view, they do not require constant coherence checks. This consistency helps to build trust.

Graphical user interfaces give us less sensory stimuli than, say, a face-to-face conversation which means less data to judge trustworthiness. The typical screen interface shows us a small area of visual data, with limited sounds and maybe some vibrations. Because the input is limited, each bit gets more attention and is judged more critically. This is why designers worry about inconsistencies down to the smallest detail. “Something looks wrong here” is not about aesthetics, it is about trust.

My favorite example is PayPal. Their checkout page, designed to generate trust, incorporates the recipient’s logo which introduces an alien element that looks different every time I see the page. It takes a leap of faith to convince myself that it isn’t a phishing site, but the real deal.

Insufficient visual coherence in PayPal's graphic interface

In a graphic interface, we have to rely on visual coherence to establish trust.

Andreas: Regarding trustworthiness, inconsistency seems to have the same effect on the perception of interfaces, than it has on the perception of humans. You cannot trust a person who has a different opinion today than tomorrow. And you cannot trust an interface which behaves and appears in to many different ways.

The time frame in which inconsistency occurs plays an important role. If a person has a different opinion today than one month later, you perhaps think the person learned a lot and because of that they changed their opinion. I think the same is true for interfaces. It`s a big difference if e.g. the PayPal page looks different very often over a relatively short period of time, or if it changes not so often. In the latter case, you perhaps think: “This is an redesign, and the changes are real improvements.”

Jonas: So consistency in the moment is more important than consistency over time. This is the antidote to the slow-acting poison of “We’ve always done it this way”. Keep doing it this way, and my user experience will be consistent over the long term. That is not necessarily bad, internal consistency even can be a point of differentiation: Coca-Cola, fixie bikes, band reunions and home cooking all promise a well-known, traditional user experience.

External consistency: consistency with the users expectations in the present moment

External consistency: consistency with the users expectations in the present moment. Photo credit: Daniel Lobo. CC BY-SA 2.0

But usually, we don’t favor internal, long-term consistency. Instead, we want short-term consistency with external factors. Does this user experience fit into my life right now? Is the interface as quick, simple, learnable, beautiful as other interfaces I am using? If the user experience is bad right now, I do not care that you’ve always have done it that way. The world has moved on while you’ve been doing it that way and ignoring the context.

To clarify: it’s not about change for the sake of change, not about following trends. Consistency in a changing world needs attention and flexibility – if you want to keep a fixed position in moving water, you need to countersteer. Take the discussion about the new logo of german mail-order/online retailer Otto: pleasantly boring, designed to stay in the middle of the mainstream. 90% of the customers likely won’t notice the change. I bet that this way exactly the goal: consistency. If the logo would not have changed, eventually the mainstream would have moved on, and it would have seemed old-fashioned. Otto had to run to stay in place, even if it is frustrating for graphic designers that want to sprint ahead or take a sudden left turn. This is why every static corporate design guideline is dangerous, an invitation to blindly follow the letter of the law with no regard for context. The spirit of the law is more important, and it demands a living corporate design. As interfaces spread through our live, they need to constantly adapt to achieve a consistent result.

Andreas: If you see a person for the first time, you know very quickly, within one tenth of a second, if you like the person and if you think that the person is trustworthy. You need longer to judge if you like an interface: it takes five seconds to build a judgment on problems in a design. Only the visual appeal of an interface can be judged very fast, within 50 milliseconds.

The question is: do people change their judgment when you give them more time? When it comes to judgment about people, the first impression is similar to the judgment after a long timespan. When it comes to judgment about interfaces you have the same effect. The judgment after five seconds is similar to the judgment after an usability test. But the exception is that the judgment after 60 seconds differs from the judgment after five seconds and the judgment after a long timespan.

When you think about if change is necessary or not, you have to be aware of the communication goals. According to your example with Otto, perhaps Otto wants to be seen as mainstream, and bases its change-decisions on this goal.

When it comes to brand recognition it makes sense to stay the same. But as you mention, the paradox is that it’s necessary to make slight changes in order to maintain the same brand recognition. For example, Coca-Cola bottles changed only slightly within a time span of 76 years. But it seems, that after 1991 they had to make bigger changes in order to maintain their brand recognitions.

Jonas: Just think about all the first impressions wasted on welcome pages and load screens. The first 50 millisecond impression of an interface is visual – a reference point for the interfaces perceived quality is set before any interaction has happened. You have mentioned that we strive for internal consistency, that changing our opinion is more difficult than reinforcing it. That makes the first impression very powerful.

The importance of the first impression also reinforces that our interfaces must be consistent with the user’s expectations most importantly. The rules we as interface designers use internally to help us achieve that consistency are secondary. If the results interrupt the user’s workflow, we must change them. A clear, beautiful example is type design. Sometimes, I think type design is a conservative discipline of visual design: limited to black and white, established glyphs and recognizable letter shapes, with legibility and centuries of tradition that must be kept in mind. With so many constraints, a typeface should be able to be put into a few rules, like one height for all capital letters. Unfortunately, human perception introduces the need for exceptions. To appear consistent, letter height must be inconsistent, as master type designer Tobias Frere-Jones shows so beautifully: “We read with our eyes, not with rulers, so the eye should win every time”.

Letter shapes are adapted to the peculiarities of human perception.

Letter shapes are adapted to the peculiarities of human perception.

Andreas: What I like very much with the type design example, is that you can achieve consistency with inconsistency. You need different letter sizes, so that all letters look the same. We have to take that into account, because we do not design for machines, but for humans. There is the same phenomenon with circles. If the height of a circle is slightly smaller than its width, it is perceived as a perfect circle by the human eye – although mathematically incorrect. This has evolutionary reasons, as Adrian Frutiger describes: “Man has always moved on a horizontal level. For this reason his vision has developed to include width rather than height, because danger predominantly came from the left and right” [5] Because of this, a vertical distance seems a lot of bigger, than the same horizontal distance.


At this point, we’ve decided to call it a day, and an article. Summarized, we found a few handy connections:

  • Consistency is predictable and learnable,
  • while inconsistency is striking and reinforcing.
  • Inconsistency can also be surprising and funny.
  • We want to be consistent ourselves to avoid cognitive dissonance.
  • Our need for coherence leads us to prefer consistency from people and from interfaces.
  • Short-term consistency beats long-term consistency,
  • and consistency with external factors beats consistency with internal rules.
  • Consistency with changing external factors demands constant adjustments – consistency through inconsistency.

Similar posts

Desktop Modern UI by Jonas Stallmeister
Jonas writes about the importance of detail consistency regarding the Modern UI style. For example, no rounded corners, not on large layout areas, not in small icons. In his post he considers Modern UI style rules which should be applied to graphical elements to ensure a consistent style.

Touching the desktop – Modern micro-interaction and burdens of the past by Maren Wolff
In her article Maren considers, among other things, whether established forms of interaction such as context menus and tooltips should also be used for touch screens. She examines Apple and Microsoft: did they apply old interaction forms consistently to touchscreens or did they decide against it?


  1. ^ Manage Your Day-to-Day; The 99U Book Series; page 90
  2. ^ Cialdini, Robert B.; Die Psychologie des Überzeugens; 6th edition; page 109
  3. ^ Cialdini, Robert B.; Die Psychologie des Überzeugens; 6. Auflage; page 94
  4. ^ Cooper, Alan; About Face; first edition 2010, german translation; page 244
  5. ^ Frutiger, Adrian; “Signs and Symbols: Their Design and Meaning”; Marix Verlag, Wiesbaden 2004; german translation
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