Consistency plays a key role in both life and design. Systems are easier to use and learn when similar parts are displayed in similar ways. It enables people to easily transfer knowledge to new contexts, learn new things fast, and eliminate confusion. When we boil it down there are four types of consistency to be aware of when designing:
1. Aesthetic Consistency
Consistency of Style and Appearance
ex: company logos, fonts, colors, graphics
Aesthetic consistency enhances recognition, communicates membership, and sets emotional expectations. For example, Adidas apparel is instantly recognizable because the company consistently features the three strip symbol in some form on all the goods they produce. The logo has become associated with fitness wear and accessories, and thus informs people about how they should feel about their goods and when to wear and use them.
2. Functional Consistency
Consistency of meaning and action
ex: Underlined links on a website, Traffic light colors, Buttons on a T.V. remote, Navigation at the top of a web page
Functional consistency improves the ability to use, learn, and navigate by enabling people to leverage existing knowledge about how the design functions. For example, websites viewed on a mobile device are now making use of a condensed navigation menu by using a three line icon (hamburger menu). This icon is used as a symbol for the navigation menu and is seen at the top of a site on a mobile device. A person can tap the menu icon and see the navigation expanded. The consistent use of this symbol by UI/UX designers has become existing knowledge about how the button functions, which makes going to other websites on a mobile device with the same symbol easier to navigate.
3. Internal Consistency
Consistency with other elements in the system
ex: Signs at a hospital, Buttons on a website, Consistent use of typography across multiple pages
Internal consistency cultivates trust with people. It is a combination of both functional and aesthetic consistency. When new instances of the design are introduced within a system like a website, on different pages of that site the user will have an easy time navigating the design.
4. External Consistency
Consistency with other elements across multiple systems/products
ex: Adobe products, Microsoft products, Apple products
External consistency broadens the benefits of internal consistency across multiple independent systems or products. It provides a great user experience because a person can take their knowledge of one product and re-use it in another. This can be seen with products from large companies like Apple, Adobe and Microsoft. Once a person knows how to use Word, they already have a better understanding of how to use Powerpoint.
When possible, it is best to achieve all four types of consistency. Aesthetic and Functional consistency are the priority and should be applied be in all aspects of design. To establish unique identities, use Aesthetic consistency. To simplify usability and ease of learning, use Functional consistency. From there, make sure that systems are always Internally consistent and Externally consistent to the greatest degree possible to ensure the best usability and happy users.