What are Affordances?

Asked to provide a personal definition of affordances, I came up with the following:

An affordance gives clues as to how the world, both in terms of the natural environment and man-made objects, can be interacted with. Designers can use affordances to make things and processes easily understandable by providing the user with a clear mental model.

In their writings, both James J. Gibson and Don Norman describe how not only form but also the materiality of things can afford specific actions.

While working in our grad studio I one day realized that most of our walls were covered with whiteboards. We use them to sketch out quick ideas, to arrange post-it noted or to map out complex concepts. But how do we know when a white board ends and the wall begins? Both are white, rectangular, vertical structures. At a quick glance we notice that one reacts with light differently than the other; one looks uniform and matte, while the other is metallic and shiny, reflecting the ceiling lights and bright windows scattered across the room. When we touch them they feel differently, too. Warm and rough yet uniform versus cold and incredibly smooth.

Both materials communicate with us and they tell us very different stories: We know that smooth and shiny surfaces are easily cleaned and that rough materials soak up paint and liquids immediately. If you were handed a pen and were told to sketch something out, on what surface would you instinctively draw on? The shiny one or the rough one?
Most of us would decide to draw on the shiny, smooth material. It affords being drawn on because of its unique surface qualities.

This however is a fallacy. Only when we use special markers can we remove our sketches afterwards. If we happen to grab a permanent marker we might end up ruining the whole whiteboard for everyone else because there is no easy way to clean up. The pen however does not communicate if its drawings can be removed afterwards or not. There is no instinctive way of differentiating between temporary and permanent markers. The only way of knowing which is which is to read the label, which by Don Norman’s definition is bad design.

There is another vertical structure in our studio that tells us a completely different story. We find it between desks, separating our individual workspaces. It feels warm and is responsive to the touch, soft and almost spongy. The material is very porous and affords being pierced by metal pins. We use it to attach notes and prints to.
Our whiteboards however can’t be used with pins. Instead we use little magnets to attach things to them. Interestingly, they look similar to their metal pin couterparts — an affordance that helps us understand their function.

All three materials discussed can be found as vertical structures in our grad studio. No one told us how to use them properly. Yet, we instinctively know how to interact with them because of their different materials. Material affords interaction.