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While discussing the need for affordances to be consistent, comments between me and JeroenEijkhof indicate we don't have a similar interpretation of the term 'affordance'.

I claimed that something being 'toggleable' (selectable) is a perceived affordance, while JeroenEijkhof draws the line at a perceived affordance of being clickable, selected/unselected only being a result of that.

The sources I found don't really help in knowing where to draw the line.

According to wikipedia:

An affordance is a quality of an object, or an environment, which allows an individual to perform an action. For example, a knob affords twisting, and perhaps pushing, while a cord affords pulling.

A further clarification by Don Norman, who introduced the term affordance to design, doesn't give a final answer either.

How broad is the definition of affordance? Could 'selectable' or 'toggleable' be considered a perceived affordance?

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5 Answers 5

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My understanding is that originally affordances meant the interactions that are physically possible owing to the form of an object. When we say a doorknob two inches in diameter affords single-hand grasping we simply mean it possible to grasp it. If it were two feet in diameter, it would not afford one-hand grasping. From our experiences, we humans learn to recognize affordance by appearance, so this can be used to guide interactions.

The original concept of affordances falls apart when you get to software user interfaces because there are no physical interactions and anything is in principle possible. A user can click anywhere. It’s just a question of if and how something will respond. In the essay you linked to, Norman attempted to clarify and expand the concept of affordances to include “perceived affordances” in addition to the real affordances that are only possible with physical interactions.

Perceive affordances, according to Norman, are “cultural constraints” and “learned conventions.” Underlined colored text “affords” clicking because users have learned that’s what indicates a link. In other words, having perceived affordances is simply being consistent with what everyone else does (and therefore what users have learned). It merely means following tradition and well-known standards. Can something afford toggling? If it looks like how toggling is traditionally distinguished from non-toggling (e.g., a checkbox), then yes. Likewise for selectable.

The concept of perceived affordance lacks rigor. How conventional does a convention have to be to qualify as an affordance? The usefulness of the concept is questionable. Why use the term “affordance” when we already have the term “consistency”? I sometimes find “affordance” useful to refer semi-formally to a metaphor, convention, or standard so ingrained in user habits as they respond to it automatically, almost compulsively. But arguments over precisely what is or isn’t an affordance are irresolvable.

The vagueness of the affordance concept can also be counterproductive. I get the impression the concept has led some UX designers to believe there are certain elemental perceptual properties that inherently communicate interactions to the user, such as gradient shading affords clicking to select, or a list of objects (on a mobile device) affords swiping to scroll. However, if we recognize affordances as synonymous with external consistency, we realize there are no elemental perceptual properties. Instead there is the holistic image and it’s similarity on multiple dimensions with previous experience. Gradient shading only works reliably on a smallish long rectangularish shape with centered text label, for example.

I would not object to “affordance” being deleted from our professional vocabulary like “user friendly” has been.

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Great answer! This covers all grounds, thanks. –  Steven Jeuris Oct 10 '11 at 17:08

There is no purely objective definition of affordance. Clear definitions are great when 1) they exist, 2) they are ubiquitous. When there are competing definitions or understandings they aren't as clear and so, it's better to explain what you mean by a particular term before you use it.

Any judgement or definition I could give you on the use of the word would just be my opinion (or that of some other person) in the same way that you and JeroenEijkhof have opinions on it.

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You stated that "A definition is simply a tool to help you communicate with other UX professionals". This is even more important when writing a thesis about the subject, which is why I asked this question in the first place. What is the point of having subjective definitions? If there is no 'official' objective definition I guess I will have to describe the way I will use it before mentioning the term. –  Steven Jeuris Oct 10 '11 at 9:04
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@StevenJeuris: Clear definitions are great when 1) they exist, 2) they are ubiquitous. When there are competing definitions or understandings they aren't as clear and so, as you suggest, it is better to explain what you mean by a particular term before you use it. –  JohnGB Oct 10 '11 at 9:20
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Consider incorporating that into your answer. The reason why I am not upvoting/accepting is because of the initial focus on no need for definitions. –  Steven Jeuris Oct 10 '11 at 9:24
    
@StevenJeuris: Good suggestion. Upon re-reading my answer I can see how it came across that way. Answer edited. –  JohnGB Oct 10 '11 at 10:25
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@StevenJeuris I think for our purposes it's most correct that there is a largely agreed on definition in HCI. There isn't a dictionary definition matching it, but that's a bit too high of a standard for a relatively new and specialized field with no standards board. Bottom line if you say "affordance" to an HCI person it has a very real and concrete meaning. –  Ben Brocka Oct 10 '11 at 15:43

I tend to describe affordances as things in the environment which are 'waving' at the user asking to be interacted with in particular ways.

Don originally made the point by pointing out how the handles on doors are 'waving' at the user, signalling how the door should be opened:

There's a picture or two on here which shows this:

http://www.quora.com/What-are-examples-of-affordances

The classic software interface example is the use of little dots to show a 'roughening' (there are some below this input window in edit mode). The little dots flagged up that if the window was a real physical object it would easier to drag it across a surface by pressing with one's finger on the 'rough' bit.

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and yet there is also invisible affordances ... like how on the iphone, the rectangular zone around each key on the keyboard grows and shrinks according to what you just typed and what you are likely to type next. It's a quality of the way the keyboard is defined that affords quick and accurate typing. –  Erics Oct 10 '11 at 12:41

My take is this: Affordance is exhibited via hints and cues that suggest from a distance how an object behaves and how a user should engage and interact correctly with an object.

Thus, via styling, drop shadow, raised effects, and other button-like attributes, from a distance you can infer that a single button is clickable, but you cannot infer that it can be toggled. The button does not present information that it can change state, and what the alternative state is, nor how many alternative states there are. Although of course you can add text, but the point is - should you need to?)

Take a couple of examples:

Consider a pushable power button, until you push it and interact with it, you do not really know whether it is a 2 state button (on/off) or a tri-state button (on/off/standby). You can make educated guess on experience and context, but in isolation, you cannot infer it from a distance, before interacting with it.

But as an alternative, consider a rocker switch like a wall light, this does afford a toggling two state behaviour. You can tell from a distance that pressing the switch should toggle the state from it's current setting to the alternative.

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Where to draw the line when culturally developed 'affordances' can be called affordances and when not? E.g. The rocker switch could have 5 states, it's only out of experiences you expect it to have two states. Similarly I can easily argue a checkbox affords toggling. –  Steven Jeuris Oct 10 '11 at 14:41

The breadth of the term depends on whom you are using it with.

In terms of UX Usability First's definition is probably the most directly relevant; affordance has come to mean what a user perceives they can do with an object.

The original definition coined by James J. Gibson in The Theory of Affordances included all possible actions an actor could take on an object. It's the only strictly objective definition, as there is a finite set of actions possible and the context of interaction and the actor are irrelevant.

We don't use this definition anymore, at least in the field of Human Computer Interaction (HCI) we use the definition in the original version of Donald Norman's book The Design of Everyday Things, where affordances are limited to readily perceptible actions. He's since stated that he miscommunicated the meaning of affordance, and what he was talking about is perceived affordance. Still within the fields of HCI and UX the definition has come to mean the more useful definition which limits affordance to readily perceptible actions.

Bottom line, in HCI and UX it's important that you convey what an item can do, not the fact that it is possible if you put an indefinite amount of time into learning a system. It's unfortunate that the word got co-opted, but the original definition of affordance is practically no longer in use, it's more of an engineer's definition of affordance, it's important, but only important to UX once it's been translated to how the user will interact with it.

To address the "clicking" vs "selecting" argument your issue is more that clicking is the affordance of the mouse, whereas selecting/ect is the affordability of the digital realm. If you only consider the physical actions than 99% of actions with a conventional desktop PC are just "press a button." The affordance you're talking about is of the interface, not the physical device, unless you're designing a mouse the clickability isn't the affordance. You can click anything anywhere, whether it does anything on the computer is another matter.

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So, yes, something being selectable/toggleable can be considered a perceived affordance in HCI research? –  Steven Jeuris Oct 10 '11 at 14:21
    
Sorry that specific thing got away from me, I think you're getting into semantics about "action" in that case. Arguably the actions are both "clicking" in a physical context, but what the user is trying to DO is select. To reduce all computer interaction to clicking and pushing buttons would be a grave misunderstanding. Updated my answer –  Ben Brocka Oct 10 '11 at 14:28
    
"If you only consider the physical actions than 99% of actions with a conventional desktop PC are just "press a button" ... good argumentation! –  Steven Jeuris Oct 10 '11 at 14:44

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