Consistency, a section written by William Lidwell, Kritina Holden and Jill Butler and featured in Universal Principles of Design (2003), defines consistency as the parts of a design that are similar allowing the system to become more usable.
The authors identify four types of consistency used in everyday life and not only in design, namely aesthetic, functional, internal and external consistency. These types of consistency entwine with principles of design and systematic elements in the environment, and they enable people to be able to learn quickly and focus their attention on relevant aspects.
Aesthetic design consistency, for example, exists within the program or the website and its use of typography and menus, that have the same uses and effects as each other to provide navigation and comfort for the user (Silver, 2004).
Similar to typography in aesthetic consistency, language as a broad term provides functional consistency and sometimes inconsistency (Laidlaw, 2013), where creating meaning and purpose through language requires questioning, challenging, mirroring, observing and inquiring (Baldwin, 2004).
Where Lidwell, Holden and Butler argue that consistency is key to a successful design, Nielsen (ed.) provides a checklist to ensure complete effectiveness, listing a simple design, a style guide, a call back code, a virtual interface, object-oriented programming and interface code generating tools (1989), and this internal consistency arrives through aesthetic and functional consistency (2003).
External consistency can be defined as the relationship between these three other elements of consistency, as to achieve external consistency with the environment, there must also be consistency within the system and its operation. This consistency can only be reached if the user is familiar and comfortable with the other elements.
Although this reading is an excerpt from a book about design, it is important to note that consistency is relative to everyday life, within our own minds and within our own actions. A lot of the norms and standards are met through consistent actions, and inconsistency is sometimes met with isolation and separation.
Baldwin, F., (2004). Creating meaning through language. Shambhala Institute. Retrieved from
Laidlaw, G., (2013, August 29). Why Consistent Language Matters. [Blog post]. Retrieved from
Lidwell, W., Holden, K., Butler, J., (2003). Consistency. Universal principles of design. Massachusetts: Rockport.
Nielsen, J., (Ed.). (1989). Coordinating user interfaces for consistency. Boston, MA: Academic Press.
Silver, M., (2004). Exploring interface design. Stamford, CT: Cengage Learning.