In the first part of this series, we talked about the foundations of visual design, exploring the seven principles of design: contrast, emphasis, balance, proportion, repetition, movement/rhythm, and unity/harmony. We also learned that visual design is different from interaction design and user experience design principles. How are they different? We can understand the differences in terms of values, since principles are ultimately rules we use to show help us adhere to our values.

UX Design principles are based on a philosophy and set of values about how to treat people so they feel respected, valued, and treated with dignity when they are using our products.

Interaction design principles are based on a philosophy and set of values about how to treat people so that they feel respected, valued, and treated with dignity when they are interacting with computer hardware and software.

Visual design principles are based on a set of values or philosophy about why objects are perceptually and emotionally appealing or provocative to people.

Interaction design principles first emerged in the 70s, rules established to govern the design of computing systems and business software – since the personal computer and software wasn’t widely available until the 1980s. Interaction design principles drew on product design principles generally . But with computing there was a special focus on the interaction between people and the computing systems and software.

One thing designers noticed early on was that, since a computer / software responds dynamically to human interaction, people tend to treat the product as more like a human than an inert object. As such, the interaction is governed by many of the same rules that apply to our social interactions. Interacting with computing systems and software is also both intellectual and emotional, so designers also drew on the insights of psychology. Insights drawn from sociology, social psychology, and cognitive psychology helped shaped the work of early interaction designers – many of whom were trained as social scientists and psychologists.

Consequently, interaction principles were also steeped in scientific observation: the psychology and sociology of perception, interpretation, and interaction. Alan Cooper was first to start developing many of the methods and tools used in interaction design, famously setting out some of his precepts in the book, The Inmates are Running the Asylum. The first person to publish a set of principles was Ben Shneiderman in 1987.

Shneiderman’s Interaction Design Principles

1. Strive for consistency
2. Cater to universal usability
3. Offer informative feedback
4. Design task flows for closure
5. Prevent errors / good error handling
6. Permit easy reversal of actions
7. Make users feel they are in control
8. Minimize short term memory load

His work was later refined by the researchers Jakob Nielsen and Rolf Molich who published their update in 1990. The interesting thing about their work was that they also tested how stable was intepretation of the principles by designers themselves. That is, when a designer evaluated a system to see if it comported with the principles, the researchers asked if the interpretations were similar, observing the decisions made by 100 different teams. It turned out that the principles were interpreted consistently.

Jakob Nielsen and Rolf Molich’s 1990 principles:

1. Use consistency, have standards
2. Ensure visibility of system status
3. Match system and real world
4. User control and freedom
5. Error prevention
6. Recognition rather than recall
7. Flexibility and efficiency of use
8. Aesthetic and minimalist design
9. Help users recognize, diagnose, recover from error
10. Provide online documentation and help

User experience design principles are steeped in the early work of interaction designers. However, UX principles apply to the relationship between the user and a broader set of interactions, and not merely the interaction between a user and the computer system or software. Instead, we think in terms of the entire user experience to also include the brand and brand identity. UX design principles are also more broadly concerned with what we might think of as higher order aspects of the experience such as emotional satisfaction, feelings of engagement, and so forth.

To understand the difference, consider that a principle common to interaction and UX design: communicate to the user the current state of the system. For instance, if someone enters an old URL and gets to a page that no longer exists, a good interaction design requires the system to let the user know that the URL no longer exists. The message might be something like this example from Microsoft:

While this message upholds the principle that we should always let the user know the status of her request to a computer system – in this case, notifying that the page is missing — it’s not exactly a warm or emotionally satisfying message. User Experience design principles would go beyond this minimal level of response, crafting messages that are more helpful, friendly, accommodating of user errors, and so forth.

In this way, you can see the difference in terms of the following mantra:

Can I use it?	Usable because it works
Should I use it?	Useful because it not only works, but works well.
Do I want to use it?	Desirable because it works, works well, and I enjoy using it

If you want to explore the ways businesses conceive of the principles that guide the user experience of their products, be sure to visit Design Principles FTW. Among them, you’ll find principles espoused by Microsoft, Google, Apple IOs, IBM, Zappos, 37 Signals, Android, Bing, and other companies. You can see how design principles are broader and more business and brand focused – and often more abstract and high level – than are interaction design principles.

You can also explore the interaction principles created by the pioneers:

Nielsen’s 10 Usability Heuristics for User Interface Design
Brucer Shneiderman’s Eight Golden Rules of Interface design
Tognazzini’s Interaction Design Principles (Apple)
Don Norman’s Principles of Design
Principles and Patterns for Rich Interaction (Theresa Neil and Bill Scott)