In Don Norman’s influential book ‘The Design of Everyday Things’ he introduced the term ‘Perceived Affordance’ (referred to as affordance) to the design community. At the time it was necessary to give a name to a fundamental aspect of their work, namely how do you communicate to a person the intended use of an object?
What is a perceived affordance?
An affordance, in design speak, is a property of an object that implies how it can be used. For example, the design of a chair affords: sitting on, being used for support when standing and standing on. These are some (not all) of the things you can do (actions) with a chair because of the way it was designed.
However, affordances still exist even if it’s not intended by the designer at all. Take an instance of a chair with wheels, the chair still affords standing on, it has height, is sturdy and has a large, flat seating area. The inclusion of the wheels make standing unsafe, the affordance is still present but that particular use is not intended.
From the moment Don introduced the term it took on a life of its own, as Don himself describes:
“When I introduced the term into design in 1988 I was referring to perceivable affordances. Since then, the term has been widely used and misused. The result has been confusion…”
The misuse lays in the problem that affordances are all the possible actions a person can take with an object, not just the designed/intended action. For example a tablet computer screen affords tapping. The inclusion of an icon (as a clue to where you tap to launch an application) does not create the affordance; it’s the properties of a tablet screen that does.
Now, 25 years later, Don has called to retire the term affordance, instead we should use signifier. Signifier more accurately describes how a designer lets a person know what to do (rather than what’s possible) by providing a clue to the desired action.
Continuing the example above the application icon is a signifier, as it indicates where on the screen you should tap to launch the app. You can’t launch that app by tapping on any other area of the screen.
You may be thinking that affordance is now a redundant principle of interaction design. I disagree, affordances are still important because of the metaphors we use.
When we choose a metaphor to represent our systems conceptual model we inherit the schema of that object. We automatically create in the user’s mind a set of possible actions.
What’s a Schema?
Schemas allow us to acquire new information quickly and efficiently by liking it to some other information already stored in memory. For example, I can describe a Zebra to someone who has never seen one as a Horse with black and white stripes. The Horse schema, if known, will allow that person to use any information they have about Horses and apply that to the Zebra. You would then know that a Zebra is black and white has: hooves, mane, tail, eats grass, and is about 5ft tall.
The downside to schemas is that they can allow for the memorisation of incorrect or incomplete information, if a person’s only experience of a horse is of the miniature variety, they will incorrectly remember that all Zebras are only 3ft tall
When computer engineers used the concept of a filing system as the way to represent stored files on a computer hard disc, they had to ensure (amongst other things) that files and folders could be easily added, renamed, moved and deleted, this is because these are some of actions available when using actual folders and files I.e. Someone who uses paper files, and folders can: label and relabel them, add additional files to existing folders and rearrange them. They can add addition files to cabinet drawers and they can throw away old files and folders. A person who uses a filing system will have expectations based upon the use and available actions of the real world counterpart.
If we don’t take time to understand the available actions of real world objects, it’s possible that we could miss a vital action which would ultimately cause frustration for the person using the system.
It seems unlikely to me that the originators of the modern file system considered the affordances of physical file and folders when designing the system. It is most likely that they were more concerned with the available restricted space on the hard disc. Had they taken time to understand the possible actions inherent in the metaphor they chose, then we might not have had an operating system that only allows filenames with 8 characters, as we did with DOS based systems.
It is still essential then for designers to understand affordances, so that they hone their ability to look at the world in terms of the available actions. Then, when choosing metaphors to represent our systems we can ensure that we have full understanding of what actions should be made available or not.
Matthew Goddard 