2.2 Design principles
As we mentioned in Section 2.1, in order to achieve usability and user experience goals, design choices need to be guided by certain principles. These design principles derive from the way our minds and bodies work.
Design principles can also be seen as building on each other, so we first introduce perceivability, because we first experience an interaction through our senses, which is a starting point for any interaction. However, in order for us to be able to make sense of an interaction, the things that we perceive need to be consistent, so we can interpret them and make predictions of what might come next. Next we talk about affordance, which can be seen as a particular kind of consistency between our potential for interaction and the interaction afforded by a product, while constraint is effectively a kind of (negative) affordance telling us where we can (not) interact. Finally, feedback tells us when we have interacted and thus signals the end of the interaction.
The following will further clarify the importance of each of the design principles.